is matter around us pure?

Question 1

is all matter around us pure?

Answer 1

all the matter around us is not pure. the matter around us is of two types:
1. pure substances.
2. mixture. ( impure substances )

Question 2

what are pure substances?

Answer 2

a pure substance is one which is made up of only one kind of particle ( atoms and molecules )
for example, sulphur element is made up of only one kind of particles. ( pure substance. ) water is also a pure substance. all the elements and compounds are pure substances because they contain only one kind of particles. thus, hydrogen, oxygen, nitrogen, chlorine, bromine, iodine, carbon, sulphur, iron, copper, silver, gold, mercury and silicon ( elements ) are pure substances and ( all the compounds ) such as water, carbon dioxide, sodium, chloride, sugar, copper sulphate are also pure substances. a pure substance is homogenous throughout its mass. a pure substance CANNOT be seperated into other kinds of matter by any physical process. a pure substance has a fixed composition, fixed melting and boiling point.

Question 3

what are impure substances?

Answer 3

impure substances: mixtures
a mixture is one which contains two or more different kinds of particles. a mixture contains two or more pure substances mixed together for e.g, milk is a mixture of water, fats, proteins, etc. all mixtures are impure substances.
some examples are: salt solution, sugar solution, milk, sea-water, air, juice, soft drinks, rocks, minerals, petroleum, tea, coffee, paint, soil and bricks. a mixture may be homogenous or heterogenous in nature. a mixture can be seperated into other kinds of matter by physical processes. a mixture does not have a fixed composition or a fixed melting or boiling point. most of the matter around us exist as mixtures of two or more pure substances.

Question 4

what are the three general classes of matter?

Answer 4

the three general classes of matter are: elements, compounds and mixtures.

pure substances: only one substance present, no impurities
[ elements : cannot be divided into simpler substances.
compounds : made from elements chemically bonded together. ]

mixture: more than one substance present
[ homogenous mixture : ( solutions ) substances completely mixed. mixture exists in one state or only one phase.
heterogenous mixture : ( suspensions and colloids ) substances seperate. one state or one phase spread throughout the other. ]

Question 5

what is solute and solvent?

Answer 5

the substance which is dissolved in a liquid to make a solution is called a solute. the liquid in which the solute is dissolved is known as a solvent.
usually, the substance present in a lesser amount in a solution is the solute, and the substance present in a larger quantity is considered the solvent. solute particles are also called dispersed particles and solvents are known as the dispersion medium. though most of the common solutes are solids even liquids and gases can also be solutes. water is the most common solute. water is an aqueous solvent. organic liquids like alcohol, carbon tetrachloride, carbon disulfide, and benzene are common non-aqueous solvents.

Question 6

what are aqueous and non aqueous solutions?

Answer 6

the solutions made by dissolving various solutes in water are known as aqueous solutions. On the other hand, the solutions made by dissolving various solutes in organic liquid are called non aqueous solutions.

Question 7

what are solutions?

Answer 7

Solution is a homogenous mixture of two or more substances. some common solutions are salt solution, sugar solution, vinegar, metal alloys, and air.

Question 8

what are true solutions.

Answer 8

salt solution and sugar solution are known as true solutions because in these solutions, the particles of salt and sugar are mixed so well with water that we cannot distinguish one from the other. the true solutions are also known as the molecular solutions because the size of dissolved particles in such solutions is the same as that of a molecule.
when we talk of a solution, it will mean a true solution or a molecular solution. some more examples are: sea water, copper sulphate solution, alcohol and water mixture, petrol and oil mixture, soda water, soft drinks, and lemonade. the substances which dissolve in water completely are said to be soluble in water. only soluble substances form true solutions.

Question 9

show a experiment to study the properties of a solution

Answer 9

if we shake some sugar with water in a beaker, the sugar seems to disappear in water and we get a transparent sugar solution. these dissolved sugar particles cannot be seen even with a microscope, and the sugar does not settle down even on keeping the solution for quite some time. if we filter the sugar solution, the whole solution passes through the filter paper and no residue is left behind. the sweet taste of the sugar solution shows that sugar is present in it.
from these observations, we can conclude that sugar solution is a homogenous mixture having the same composition throughout. sugar solution is a true solution. the particles of the solute break up to such an extent that they disappear into the spaces between the solvent molecules. a sugar solution does not scatter a beam of light passing through it and render its path visible because the sugar particles in it are so small that they cannot reflect light rays falling on it.

Question 10

what are the properties of a solution?

Answer 10

1. a solution is a homogenous mixture
2. the size pf solute particles in a solution is extremely small. it is less than 1nm. 1 nanometre = 10^-9
3. the particles of a solution cannot be seen even with a microscope.
4. the particles of a solution cannot be seperated. so, a solution cannot be seperated by filtration.
5. the solutions are very stable. the particles of solute present in a solution cannot be seperated out on keeping.
6. a true solution does not scatter light. this is because its particles are very, very small.

Question 11

what are the types of solution?

Answer 11

1. solution of solid in a solid.
   [ metal alloys are the solutions of solids in solids. brass is a solution of zinc in copper. brass is prepared by mixing molten zinc with molten copper and cooling their mixture. ]
2. solution of a solid in a liquid.
   this is the most common type of solutions. sugar solution and salt solution are the solutions of solid in a liquid. the solution of iodine in alcohol, called a tincture of iodine is also a solution of a solid in a liquid.
3. solution of liquid in a liquid.
   vinegar is a solution of acetic acid ( ethanoic acid ) in water.
4. solution of gas in a liquid.
   soda-water is a solution of carbon dioxide gas in water.
5. solution of a gas in a gas.
   air is a solution of gases like oxygen, argon, carbon dioxide and water vapour, etc., in nitrogen gas. nitrogen is the solvent in air and all the other gases are solutes

Question 12

what are the terms used to distinguish metal elements from non metal elements?

Answer 12

the terms are malleability, ductility, brittleness.
1. malleability: the property which allows the metals to be hammered or beaten into thin sheets.
2. ductility: the property which allows the metals to be drawn into thin wires without breaking.
3. brittleness: the property due to which non-metals break into pieces on hammering. brittleness is the opposite of malleability and ductility.

Question 13

explain what is meant by suspensions.

Answer 13

substances which are insoluble in water form suspensions. a suspension is a heterogenous mixture in which the small particles of a solid are spread throughout a liquid without dissolving in it. some common examples are : chalk water mixture, muddy water, milk of magnesia, sand particles suspended in water and flour in water. milk of magnesia is a suspension of magnesium hydroxide in water. solid particles and liquid remain seperate in a suspension. the particles do not dissolve in water

Question 14

give an experiment to study the properties of a suspension

Answer 14

if we shake some chalk powder with water in a beaker, a milky suspension is formed. we can see the fine particles of chalk suspended throughout the water without dissolving in it. if this suspension of chalk and water is kept undisturbed for some time, the chalk particles settle down at the bottom of the beaker. this means that chalk and water suspension is unstable. if we filter the chalk and water, the chalk particles are left behind as a residue on the filter paper and clear water is obtained as a filtrate. this means that chalk and water suspension can be seperated into chalk and water by filtration. if a beam of light is passed through a chalk and water suspension, it scatters the beam of light and renders its path visible inside it.

Question 15

what are the properties of a suspension?

Answer 15

1. a suspension is a heterogenous mixture.
2. the size of solute particles in a suspension is quite large. it is larger than 100nm in diameter
3. the particles of a suspension can be seen easily.
4. the particles of a suspension do not pass through a filter paper. so a suspension can be seperated by filtration.
5. the suspension are unstable. the particles of a suspension settle down after some time.
6. a suspension scatters a beam of light passing through it because its particles are quite large.

Question 16

what are colloids?

Answer 16

a colloid is a kind of solution in which the size of solute particles is intermediate between those in true solutions and in suspensions. the size of solute particles in a colloid are bigger than that of a true solution but smaller than those in suspensions. although, colloids appear homogenous to us but actually they are found to be heterogenous when observed through a high power microscope. a colloid is not a true solution. some of the examples are : soap solution, strach solution, milk, ink, blood, jelly and solutions of synthetic detergent. colloids are also known as colloidal solutions.

Question 17

show an experiment to show the properties of a colloid.

Answer 17

if we shake some soap powder with water in a beaker, we get a colloidal solution which is not perfectly transparent, it is somewhat translucent. we cannot see the soap particles. if the soap solution is kept undisturbed for some time, it does not settle down showing it is quite stable. if we filter the soap solution, the whole solution passes through the filter paper and no residue is left behind. all these observation indicate that the soap and water are true solutions. the scattering of light by a soap solution and the observation of the soap solution under a microscope, however, show that soap solution is not a true solution.
in a true solution, the solute particles are so small that they can not scatter or reflect light rays falling on them. for example.,, if a beam of light is put on a true solution, kept in a dark room, in a beaker, the path of light beam is not visible. the beam of light can only be visible only when the solute particles are big enough to reflect light falling on it. since the particles of a true solution do not scatter light, we conclude that they must be very very small.
in a colloidal solution, the particles are big enough to scatter light. if a beam of light is put on a colloidal solution, kept in a beaker in a dark room, the path of light beam is illuminated and becomes visible when seen from the side. the path of light beam becomes visible because the colloidal particles are big enough to scatter light. the scattering of light by colloidal particles is known as tyndall effect. the scattering of light by colloids tells us that the colloidal particles are much bigger than the particles of a true solution and hence, colloidal solutions are not true solutions. a true solution does not show the tyndall effect but a colloid does.
the particles of some colloids can be seen through a high power microscope. if a drop of milk is examined under a microscope, we can see the small particles of fat floating in the liquid. hence, colloids are heterogenous in nature, though they appear to be homogenous.

Question 18

what are the properties of colloids?

Answer 18

1. a colloid appears to be homogenous but actually is heterogenous.
2. the size of particles in a colloid is bigger than those in a true solution but smaller than those of suspension. it is between 1nm and 100nm in diameter.
3. the particles of most of the colloids cannot be seen even with a microscope.
4. the particles of a colloid can pass through a filter paper. a colloid cannot be seperated by filtration.
5. the colloids are quite stable. the particles of a colloid do not seperate out on keeping.
6. a colloid scatters a beam of light passing through it because its particles are fairly large.

configuration can be used to seperate the colloidal particles from a colloidal solution.

Question 19

how to distinguish a colloid from a solution?

Answer 19

1. the solution which scatters a beam of light passing through it and renders its path visible, will be a colloid.
2. the solution which does not scatter a beam of light passing through it and not render its path visible will be a true solution.

Question 20

explain the classification of colloids?

Answer 20

colloids do not involve only solids and liquids, they may also involve gases. colloids are classified according to the physical state of dispersed phase ( solute ) and the dispersion medium ( solvent )
most of the colloids can be classified into the following seven groups:
1. sol
2. solid sol
3. aerosol
4. emulsion
5. foam
6. solid foam
7. gel
all these are the technical names of the groups of colloids.

Question 21

describe the classification of colloids in brief.

Answer 21

1. sol
   sol is a colloid in which tiny solid particles are dispersed in a liquid medium. examples are: ink, soap solution, starch solution and most paints.
2. solid sol:
   solid sol is a colloid in which solid particles are dispersed in a solid medium. examples are: coloured gemstones ( like ruby glass )
3. aerosol
   an aerosol is a colloid in which a solid or liquid is dispersed in a gas ( including air )
   examples ( solid in gas ) are: smoke ( soot in air ), and automobile exhausts. examples ( liquid in gas ) are: hairspray, fog, mist, and clouds
4. emulsion
   an emulsion is a colloid in which minute droplets of one liquid are dispersed in another liquid which is not miscible with it. examples: milk, butter and face cream.
5. foam
   the foam is a colloid in which a gas is dispersed in a liquid medium. examples: soap bubbles, shaving cream and beer foam.
6. solid foam
   the solid foam is a colloid in which a gas is dispersed in a solid medium. example: insulating foam, foam rubber and sponge.
7. gel
   the gel is a semi-solid colloid in which there is a continuous network of solid particles dispersed in a liquid. examples are: jellies and gelatin

Question 22

give the classification of solids in a tabular form

Answer 22

page no. 243

Question 23

explain the concentration of a solution.

Answer 23

a solution may have a small amount of solute dissolved in it while another solution may have a large amount of solute dissolved in it. the solution having a small amount of solute is said to have low concentration. it is known as a dilute solution. the solution having a large amount of solute is said to be of high concentration. it is known as a concentrated solution. the concentration of a solution is the amount of solute present in a given quantity of the solution. the concentration of a solution can be expressed in a number of different ways.

Question 24

how is the concentration of a solution expressed? in solid solute dissolved in a liquid solvent.

Answer 24

the most common way of expressing the concentration of a solution is the percentage method. the percentage method refers to the percentage of solute present in the solution. the percentage of solute can be ‘by mass’ or ‘by volume’ if the solution is of a solid solute dissolved in a liquid, then we consider the mass percentage. in case of solid solute dissolved in liquid, the concentration of a solution is defined as the mass of solute in grams present in 100 grams of the solution.
concentration of solution = (mass of solute) * 100/mass of solution
mass of solution= mass of solute + mass of solvent
we do not consider the value of solids in making solutions

Question 25

explain the case of a liquid solute dissolved in a liquid solvent. how is the concentration expressed in this case?

Answer 25

if the solution is of a liquid solute dissolved in a liquid solvent, then we usually consider the volume percentage of solute. so, in the case of a liquid solute dissolved in a liquid solvent: the concentration of a solution is defined as the volume of solute in millilitres present in 100 millilitres of the solution.
concentration of solution = (volume of solute) * 100/ volume of solution
volume of solution = vol. of solute + vol. of solvent

Question 26

how can solutions be classified as saturated and unsaturated?

Answer 26

when we dissolve a solute in a solvent, then a solution is formed. we can dissolve different amounts of solute in the same quantity of solvent. in this way, we can get many solutions having different concentrations of the same solute. a particular solution may contain less amount of the dissolved soute whereas another solution may contain more amount of solute in it. so depending on the amount of solute present, the solutions can be classified as saturated and unsaturated.

Question 27

explain unsaturated solution in detail.

Answer 27

unsaturated solution:
a solution in which more quantity of solute can be dissolved without raising its temperature. for example, if in an aqueous solution of salt, more of salt can be dissolved without raising its temperature, then this salt solution will be an unsaturated solution. an unsaturated solution contains lesser amount of solute than the maximum amount of solute which can be dissolved in it.

Question 28

what is a saturated solution? explain.

Answer 28

a solution in which no more solute can be dissolved at that temperature, is called a saturated solution. for example, if in an aqueous salt solution, no more salt can be dissolved at that temperature, then that salt solution will be a saturated solution. thus, a saturated solution contains the maximum amount of solute which can be dissolved in it at that temperature. it is obvious that a saturated solution contains greater amount of solute than an unsaturated solution.
1. a maximum of 32 grams of potassium nitrate can be dissolved in 100 grams of water at a temp. of 20 degree celcius. so, a saturated solution of potassium nitrate at 20 degree celcius contains 32 grams of potassium nitrate dissolved in 100 grams of water.
2. a max. of 36 grams of sodium chloride can be dissolved in 100 grams of water at a temp. of 20 degree celcius. so, a saturated solution of sodium chloride at 20 degree celcius contains 36 grams of sodium chloride dissolved in 100 grams of water.

Question 29

how can we test whether a given solution is saturated or not?

Answer 29

in order to test whether a given solution is saturated or not, we should add some more solute o the solution and try to dissolve it by stirring ( keeping the temp. constant ). if more solute does not dissolve in the given solution, then it will be a saturated solution; but if more solute gets dissolved, then it will be a unsaturated solution.

Question 30

what is the effect of heating and cooling on a saturated solution.

Answer 30

a solution is saturated at a particular temp. only. so, if a saturated solution at a particular temp. is heated to a higher temp., then it will become unsaturated. this is because the solubility of a solution increases on heating on heating and more solute can be dissolved by increasing the temperature. the solubility of a solute CAN NOT be increased indefinitely on raising the temperature. if a saturated solution available at a particular temp. is cooled to a lower temp., then some of its dissolved solute will seperate out in the form of solid crystals. the solubility of solute in the solution decreases on cooling.

Question 31

how to prepare a saturated solution?

Answer 31

we will describe the preperation of a saturated solution of a substance, say sodium chloride at a temp. of 30 degree celcius. we take some water in a beaker and heat it with the help of a burner. now start adding sodium chloride salt to the hot water and stir it with a glass rod continuously so the sodium chloride goes on dissolving in water. we take the temp. of water upto 30 degree celcius and keeping this temp. constant, go on adding sodium chloride till no more sodium chloride dissolves in it and some sodium chloride is also left undissolved at the bottom. the contents of the beaker are now filtered through a filter paper arranged in a funnel. the clear solution obtained in the form pf filtrate is the saturated solution of sodium chloride.
when the saturated solution of sodium chloride at 30 degree celcius is allowed to cool, then the crystals of solid sodium chloride will reappear in the solution. on cooling, the solubility of sodium chloride in water decreases due to which some of the dissolved sodium chloride seperates out from the solution and forms crystals.

Question 32

what is the solubility of solutes?

Answer 32

the max. amount of a solute which can be dissolved in 100 grams of a solvent at a specified temp. is known as the solubility of that solute in that solvent at that temperature. if the solvent is water, then we can define solubility as: the max. amount of a solute which can be dissolved in 100 grams of water at a given temp. is known as the solubility of that solute in water. in other words, the solubility of a solute in water at a given temp. is the number of grams of that solute which can be dissolved in 100 grams of water to make a saturated solution.

Question 33

give examples to explain the solubility. what is the solubility of different substances in water at 20 degree celcius?

Answer 33

1. a maximum of 32 grams of potassium nitrate can be dissolved in 100 grams of water at 20 degree celcius, therefore, the solubility of potassium nitrate in water is 32 grams at 20 degree celcius.
2. copper sulphate ___ 21g ( at 20 degree celcius )
3. potassium chloride ___ 34g ( at 20 degree celcius )
4. sodium chloride ___ 36g ( at 20 degree celcius )
5. ammonium chloride ___ 37g ( at 20 degree celcius )
6. sugar ___ 204g ( at 20 degree celcius )
   in order to calculate the solubility of a substance, all we have to do is find the mass of the substance dissolved in 100 grams of water.

Question 34

what are the effects of temp. and pressure on solubility?

Answer 34

1. the solubility of solids in liquids usually increases on increasing the temp. and decreases on decreasing the temperature.
2. the solubility of solids in liquids remains unaffected by the change in pressure.
3. the solubility of gases in liquids usually decreases on increasing the temp. and increases on decreasing the temperature.
4. the solubility of gases in liquids increases on increases on increasing the pressure and decreases on decreasing the pressure.

Question 35

what are the solubilities of copper sulphate in water at different temperatures?

Answer 35

10 degree celcius __ 14g
20 degree celcius __ 17g
30 degree celcius __ 21g
40 degree celcius __ 24g
50 degree celcius __ 34g
60 degree celcius __ 40g
70 degree celcius __ 47g

Question 36

what happens when we cool a saturated solution?

Answer 36

when we cool a saturated solution of copper sulphate made in 100 grams from, say 70 degree celcius to 20 degree celcius, then the solubility will be equal to ( 47 - 21 ) grams = 26 grams of copper sulphate will seperate out from the solution in the form of solid crystals.

Question 37

what are elements?

Answer 37

an element is a substance which cannot be split into two or more simpler substances by the usual chemical methods by applying heat, light or electric energy. ( oxygen cannot be broken into simpler substances by chemical methods. ) they cannot be split because they are made up of only one kind of atoms. so, an element is a substance which is made of only one kind of atoms. ( copper metal is made of only one kind of atoms called “copper atoms”
there are 118 atoms know at present, out of which 92 of them occur in nature while the remaining are man made. every substance in this world is made up of one or more of these elements. some common elements are hydrogen, helium, oxygen, nitrogen, carbon, sulphur, etc.
diamond and graphite are also elements. elements can be solids, liquids and gases. sodium and carbon are solids. mercury and bromine are liquids. hydrogen and oxygen are gases. majority of the elements are solids. eleven elements are gases and only two elements are liquid at room temperature.
most of the materials around us are made up of two or more elements. for example, water is made up two elements, hydrogen and oxygen. sugar is made up of three elements, carbon, hydrogen and oxygen. even the human body is made up of complex compounds formed by the combination of only certain elements. the human body contains 65% oxygen, 18% carbon, 10% hydrogen, 3% nitrogen, 2% calcium and 2% other elements.

Question 38

on the basis of their properties, all the elements can be divided into three groups. what are they?

Answer 38

1. metals
2. non metals
3. metalloids

Question 39

what are metals? what are alloys?

Answer 39

a metal is an element that is malleable and ductile and conducts electricity. some examples are zinc, copper, silver, gold, tin, lead, mercury, cadmium etc.
all metals except for mercury are solids.
alloy is a metal made by combining two or more metallic elements, especially to give greater strength or resistance from corrosion.

Question 40

what are the properties of metals?

Answer 40

1. malleable
   Metals can be beaten into thin sheets with a hammer without breaking. gold and silver metals are some of the best malleable metals. aluminium and copper metals are also highly malleable metals. these thin sheets are known as foils. milk bottle caps are also made from aluminium foil.
2. ductile
   metals can be drawn or stretched into thin wires. all the metals are not equally ductile. gold and silver are among the best ductile metals. for example, just 100 milligrams of a highly ductile metal such as silver can be drawn into a thin wire about 200 m long. it is due to the properties of malleability and ductility that metals can be given different shapes.
3. good conductors of heat and electricity
   metals allow heat and electricity to pass through them easily. metals are generally good conductors of heat. the conduction of heat is also called thermal conductivity. silver is the best conductor of heat. copper and Aluminium metals are also very good conductors of heat. thus, cooking utensils are usually made of copper or aluminium metals. the poorest conductor of heat is lead. mercury is also a poor conductor of heat.
   metals offer very little resistance to the flow of electric current and hence show high electrical conductivity. silver is the best conductor of electricity. copper is the next best conductor, followed by gold, aluminium and tungsten. thus, electric wires are made of copper and Aluminium metals. iron and mercury offer comparatively greater resistance to the flow of current so they have lower electrical conductivity.
4. lustrous and can be polish
   gold, silver and copper are shiny metals and they can be polished. the property of a metal of having a shining surface is called metallic lustre. the shiny appearance of metals make them useful in making jewellery and decoration pieces. the shiny surface of metals makes them good reflectors of light. silver is an excellent reflector of light.
5. generally hard.
   most metals are hard. however, all the metals are not equally hard. sodium and potassium are soft metals and they can be easily cut with a knife. metals like iron, copper, aluminium, etc. are very hard and they cannot be cut with a knife.
6. usually strong. they have a high tensile strength
   metals can hold large weights without breaking. iron metal which is in the form of Steel, is very strong and has a high tensile strength. due to this, iron metal is used in the construction of bridges, buildings, railway lines, etc.
   however, not all metals are strong. sodium and potassium metals are not strong and they have a low tensile strength.
7. solid at room temp.
   all the metals like iron, copper, aluminium, silver, gold, etc. are solid at room temperature. only one metal, mercury, is liquid at room temperature.
8. generally have high melting and boiling points.
   most of the metals melt and vaporise at high temperatures. iron is a metal having a high melting point of 1535 degree celcius. copper metal has a melting point of 1083 degree celcius. there are, however, some exceptions. sodium and potassium have low melting points ( less than 100 degree celcius. ) gallium has such a low melting point that it starts melting in our hand due to body heat.
9. high densities
   metals are heavy substances. the density of iron is 7.8g/cm³ which is quite high. there are however, exceptions. sodium and potassium have low densities and they are light metals.
10. sonorous
    metals make a ringing sound when struck. due to the property of sonorousness of metals, they are used for making bells, plate type musical instruments like cymbals and wires for stringed musical instruments
11. usually have a silver or grey colour
    usually metals have a silver or grey colour, except for copper which has a reddish brown colour and gold which has a yellowish colour.

Question 41

what are non metals?

Answer 41

a non metal is an element that is neither malleable nor ductile, and does not conduct electricity. some examples of non metals are carbon, sulphur, oxygen, hydrogen, nitrogen, fluorine, chlorine, bromine, iodine, helium, neon, argon, krypton, and xenon. diamond and graphite are also non metals. they are the allotropic forms of carbon. all the non metals are solids or gases, except bromine which is a liquid at room temperature.
though non metals are small in number as compared to metals, they still play a very important role in our life. life would not have been possible without the presence of non metals on earth. for example, carbon is one of the most important non metal because all the life on the earth is based on carbon compounds. this is because the carbon compounds like proteins, fats, carbohydrate, vitamins and enzymes, etc., are essential for the growth and development of living organisms. another non metal oxygen is equally as important for the existence of life. oxygen is essential for breathing as well as the combustion of fuels which provide us energy for various purposes.

Question 42

what are the properties of non metals?

Answer 42

the physical properties of non metals are the opposite of the physical properties of metals

1. brittle. not malleable
   non metals cannot be be beaten into thin sheets with a hammer. they break into small pieces when hamered. for example, Sulphur and carbon cannot be beaten in the thin sheets. we cannot get thin sheets from non metals. brittleness is a characteristic property of solid non metals.
2. not ductile
   non metals cannot be drawn into wires and can easily snap on stretching.
3. bad conductors of heat and electricity
   non metals do not allow heat and electricity to pass through them. many of the non metals are insulators. there are some exceptions. diamond is a non metal which is a good conductor of heat and graphite is a good conductor of electricity. thus, graphite is used for making electrodes ( as that in dry cells )
4. not lustrous and dull in appearance.
   non metals do not have lustre which means that non metals do not have a shining surface. they have a dull appearance. however, iodine is a non metal having a lustrous appearance.
5. generally soft
   most of the solid non metals are quite soft. they can be easily cut with a knife. however, diamond which is an allotropic form of carbon is the hardest natural substance known.
6. low tensile strength
   non metals cannot hold large weights.
7. may be solid, liquid or gases at the room temperature
   non metals can exist in all the three physical states.
   Sulphur and phosphorus are solid non metals. bromine is a liquid. hydrogen, oxygen, nitrogen and chlorine are gaseous.
8. comparatively low melting and boiling points
   except for graphite which is a non metal having a very high melting point. sulphur has a low melting point of 119 degree Celsius but graphite has a very high melting point of 3700 degree Celsius. majority of the non metals have very low boiling points due to which they exist as gases at room temperature.
9. low densities
   sulphur is a non metal having a low density of 2 g/cm³, which is quite low. however, iodine has high density.
10. not sonorous
11. different colours
    sulphur is yellow, Phosphorus is white or red, graphite is black, chlorine is yellowish green, bromine is reddish brown whereas hydrogen and oxygen are colourless.

Question 43

what are metalloids?

Answer 43

there are a few elements which show some properties of metals and other properties of non metals. for example, they look like metals but they are brittle like non metals, they are semiconductors. the elements which show some properties of metals and some other properties of non metals are called metalloids
their properties are intermediate between the properties of metals and nonmetals. metalloids are also sometimes called semi metals
the important examples of metalloids are boron (B), silicon (si) and germanium (Ge)

Question 44

what is a mixture?

Answer 44

a mixture is a substance which consists of two or more elements or compounds not chemically combined together. for example, air, water, argon, carbon dioxide and water vapour, etc. gun powder is a mixture of potassium nitrate, sulphur and charcoal whereas brass is a mixture of copper and zinc. all the solutions are mixtures. salt solution ( brine ) is a mixture of common salt ( potassium chloride ) in water.
some examples are sea water, ink, kerosene, petrol, petroleum, lime-water, paint, glass coal, soil, blood, starch solution, starch solution, iron, soda water, vinegar, smoke, hair spray, shaving cream, face cream, fog and mist.

Question 45

what are the type of mixtures?

Answer 45

mixtures are of two types:
1. homogenous
2. heterogenous.

Question 46

what are homogenous mixtures?

Answer 46

Those mixtures in which the substances are completely mixed together and indistinguishable from one another, are called homogenous mixtures. a homogenous mixture has a uniform composition throughout its mass. It has no visible boundaries of separation between the various constituents. A mixture of sugar in water is a homogenous mixture because all the parts of the sugar solution have the same sugar water composition and appear to be equally sweet. A mixture of two or more miscible liquids is also an example of a homogenous mixture. For example, a mixture of alcohol and water. unpolluted air is an example of a homogenous mixture. all the homogenous mixtures are known as solutions. some examples are air, copper sulphate solution, lemonade, vinegar, kerosene, oil and petrol. Kerosene and petrol are not single substances, they are mixtures of various compounds of carbon and hydrogen ( called hydrocarbons. )

Question 47

what are heterogenous mixtures?

Answer 47

Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles, droplets or bubbles, are called heterogeneous mixtures. Heterogeneous mixture does not have a uniform composition throughout its mass. It has visible boundaries of separation between the various constituents. the mixture of sugar and sand is a heterogeneous mixture because different parts of this mixture will have different sugar-sand main compositions. Some parts of the mixture will have more sugar particles whereas other parts will have more of sand particles. There is a visible boundary of separation between sugar and sand particles. The suspension of solids in liquids can also be heterogeneous mixtures. For example, suspension of chalk in water.
a mixture containing two or more immiscible liquids is also a heterogenous mixture. for example, water and petrol. some examples are sugar and sand mixture, salt and sand mixture, gunpowder, ink, milk, paint, glass, coal, soil, wood, blood, muddy river water, hair spray, fog, mist etc.
most of the mixtures are heterogeneous mixtures, only solutions and alloys are homogenous mixtures

Question 48

what are the properties of a mixture of iron and sulphur?

Answer 48

When iron filing or iron powder and sulphur powder are mixed together, a greyish yellow mixture is obtained. The properties of this mixture are:

1. If we put a magnet in the mixture of iron filings and Sulphur, the iron particles are attracted by the magnet, so sulphur ( which is not attracted by the magnet ) is left behind. thus, a mixture of iron filings and sulphur has been separated into its constituents, by the physical method of using a magnet. Alternatively, if shake the mixture with an organic liquid known as carbon disulphide ( CS² ), then sulphur dissolves in it but iron doesn’t. On filtration, iron is obtained as a residue and sulphur is recovered from the filtrate by evaporating carbon disulphide.
2. if dilute sulphuric acid is added to the mixture of iron filings and sulphur, the iron part reacts with sulphuric acid and hydrogen gas is produced which is a colourless and ordourless gas. sulphur remains unchanged. This shows that a mixture of iron and sulphur shows the properties of iron. Now, if this mixture is treated with carbon disulphide, the sulphur part dissolves in it leaving the iron unchanged. This means the mixture also the properties of sulphur. If we combine these two results, we can say that the mixture of iron filings and sulphur shows the properties of both its constituents, iron as well as sulphur. We conclude, a mixture shows the properties of all the constituents present in it.
3. when iron filings are mixed with sulphur powder to prepare the mixture, heat is neither evolved nor absorbed. In general, energy is usually neither given out nor absorbed in the preparation of a mixture. so, the formation of a mixture is a physical change.
4. We can mix any amount of iron filings and sulphur powder to get mixtures having different compositions. Thus, a mixture of iron filing and sulphur has a variable composition. since, its composition is variable, no definite formulae can be given to the mixture of iron filings and sulphur. we conclude, a mixture does not have a definite melting point, boiling point, etc.
5. if we examine the mixture of iron filings and sulphur powder with a magnifying glass, it is found that though the iron particles are quite close to the sulphur particles, at some places there are more of iron particles whereas at other places there are more of sulphur particles. so, a mixture of iron filings and sulphur is not homogenous, it is heterogeneous. Though most of the mixtures are heterogeneous, some mixtures called solution and alloys are, however, heterogenous.

Question 49

what are compounds?

Answer 49

a compound is a substance made up of two or more elements chemically combined in a fixed proportion by mass. water is a compound made up of two elements, hydrogen and oxygen, chemically combined in a fixed proportion of 1:8 by mass ( atomic masses : H = 1u ( unit ), O = 16u, so H² : O = 2u : 16u or 1 : 8 ). similarly, common salt ( NaCl ) is a compound made up of two elements, Sodium and chlorine. Ammonium chloride ( NH4Cl ) is a compound made up of three elements, nitrogen, hydrogen and chlorine; sand ( silicone dioxide, SiO2 ) is a compound of silicon and oxygen. Marble ( calcium carbonate, CaCo3 ) is a compound made up of calcium, carbon and oxygen
some more examples are:
ammonia ( NH3 ),
carbon dioxide ( CO2 ),
ice & steam ( H2O ),
chalk ( calcium carbonate ), limestone ( calcium carbonate, CaCO3 ),
lime or quicklime ( calcium oxide, CaO ),
slaked like ( calcium hydroxide, ca(OH)2 ),
methane ( CH4 ),
glucose ( C₆H₁₂O₆ ),
sugar or canesugar ( C₁₂H₂₂O₁₁ ),
starch [ ( C6H10O5 )n ],
baking soda ( sodium hydrogencarbonate, NaHCO3 ),
washing soda ( sodium carbonate, Na2CO3 ),
Potassium Nitrate ( KNO3 ),
Potassium Sulphate ( K2SO4 ),
Sodium sulphate ( Na2SO4 ),
Copper sulphate ( CuSO4 ),
Iron sulphide ( FeS ),
Hydrochloric acid ( HCl ),
Sulphuric acid ( H2SO4 ),
Nitric acid ( HNO3 ),
hydrogen Bromide ( HBr ),
Sodium hydroxide ( NaOH )

Question 50

compounds can further be divided into three classes, on the basis of their properties. what are the three classes?

Answer 50

Compounds can be further divided into 3 classes: acids, bases and salts, on the basis of their properties. For example, ** sulphuric acid is an acid, Sodium Hydroxide is a base Where are sodium sulphate is a salt.**

Question 51

Explain the properties of a compound of iron and sulphur.

Answer 51

When the mixture of iron filings in sulphur powder is heated, a black compound known as iron sulphide ( FeS ) is formed. The properties are:

1. if a magnet is put in the iron sulphide compound, iron does not get separated from sulphur. Even carbon disulphide solvent cannot separate the sulphur from iron sulphide compound. we conclude that a compound cannot be separated into its components by physical methods.
2. When dilute sulphuric acid is added to iron sulphide compound, we get a colourless, foul smelling gas called hydrogen sulphide which has the smell of rotten eggs. No hydrogen gas is formed in this case. This mean that iron sulphide does not show the properties of iron present in it, even the sulphur present in it cannot be dissolved by carbon disulphide. thus, iron sulphide compound does not show the properties of its constituents. so, we conclude that the properties of a compound are entirely different from those of its constituent element.
3. Iron sulphide compound is prepared by heating together iron filings and sulphur. Once the reaction starts, a lot of heat and light are produced during the preparation of the compound. From this we conclude that energy is usually either given out or absorbed during the preparation of a compound. thus, the formation of a compound is a physical change.
4. Iron sulphide compound is prepared by heating together 7 parts by mass of iron and 4 parts by mass of Sulphur ( atomic masses : Fe = 56u, S = 32u so, Fe: S = 56u : 32u or 7 :4 ) if we take more of iron or sulphur, the excess part remains unreacted. thus, iron sulphide compound is always made up of the same element, iron and sulphur, combined together in a fixed proportion by mass. The composition of iron sulphide compound is fixed, it has a definite formula ( FeS ). we conclude that the composition of a compound is fixed, the constituents are present in a fixed proportion by mass. Compound has a definite formula.
5. Iron sulphide compound melts at a definite temperature. we conclude that a compound has a fixed melting point, boiling point, etc.
6. if the iron sulphide compound is viewed through a magnifying glass, no seperate particles of iron or sulphur can be see and it appears to be the same throughout its mass. we conclude that a compound is a homogenous mixture.

Question 52

what is the difference between mixtures and compounds?

Answer 52

MIXTURES :
1. a mixture can be seperated into it constituents by physical processes ( like filtration, evaporation, sublimation, distillation etc. )
2. shows the properties of its constituents.
3. energy is usually neither given out nor absorbed in the preparation of mixtures.
4. the composition of a mixture is variable. the constituents can be present in any proportion by mass. Mixture does not have a definite formula
5. Does not have a fixed melting point, boiling point, etc.
. . .
COMPOUNDS:
1. A compound cannot be separated into it constituent by physical processes. the constituents can only be seperated by chemical processes.
2. the properties of a compound are entirely different from those of its constituents.
3. energy is usually given out or absorbed in the preperation of a compound.
4. the composition of a compound is fixed. the constituents are present in fixed proportion by mass. a compound has a definite formula
5. has a *fixed melting point, boiling point, etc. )

. . though a compound is always homogenous, a mixture may be heterogenous or homogenous. so, being homogenous or heterogeneous is usually not helpful in deciding whether a substance is a mixture or a compound and, therefore, this point has not been included above.

Question 53

explain the case of solutions.

Answer 53

the solution are homogenous substances and heat is also usually evolved or absorbed in the preparation of a solution. Even then a solution is considered a mixture because:
1. it can be seperated into its components by * physical methods.
2. it shows the properties of its constituents.
3. it has a variable composition.
4. it does not have a fixed boiling point.
Suppose we are given two liquids, one a pure compound and the other a solution. to find out which one is a compound and which one is a solution/mixture, we shall evaporate them separately. The liquid which evaporates completely and leaves no residue, is a pure compound. On the other hand, the liquid which leaves behind a residue on evaporation, is a solution or mixture.

Question 54

explain the case of alloys.

Answer 54

alloys are homogenous mixtures of metals and cannot be separated into their components by physical methods. Even then an alloy is considered a mixture because:
1. shows the properties of its constituents.
2. variable composition
for examples, brass is considered a mixture because it shows the properties of its constituents copper and zinc and it has a variable composition ( the amount of zinc can vary from 20 to 35 percent.)

Question 55

on the basis of whether new substances are formed of not, we classify changes into two groups. what are these two groups?

Answer 55

There are some changes during which no new substances are formed. On the other hand, there are some other changes during which new substances are formed. On the basis of whether new substances are formed or not, we classify all the changes into two groups: physical changes and chemical changes.

Question 56

what are physical changes?

Answer 56

Those changes in which no new substances are formed, are called physical changes. in a physical change, the substances involved do not change their identity. They can we easily returned to their original form by some physical processes. This means that physical changes can be reversed. The changes in physical state, size and shape of a substance are physical changes. Some common examples of physical changes are: melting of ice, freezing of water, condensation of steam, making a solution, glowing of an electric bulb, and breaking of a glass tumbler.

1. The formation of ice, melting of ice, formation of steam and condensation of steam are all physical changes because ice, steam and water look different from one another, but they are all made of water molecules. No new chemical substance is formed.
2. When salt is added to water, a change takes place to make the salt solution. Let us now heat the salt solution until all the water evaporates, a white powder is left behind. If we taste this white powder, we will find that it is the common salt, which we had earlier dissolved in water. This means that no new chemical substance has been formed. thus, the making of a solution is a physical change
3. When an electric bulb is switched on, an electric current passes through its filament. The filament of the bulb becomes white and hot and glows to give light. When the current is switched off, the filament returns to its normal condition and the bulb stops glowing. No new substance is formed during this process.
4. When a glass tumblr breaks, it forms many pieces. however, the broken pieces are still glass. so, only the shape and size of glass has changed but no new substance is formed.

Some more examples are melting of wax, melting of butter, mixing of iron filings and sand, sublimation of a solid, making of soda water by dissolving carbon dioxide in water, formation of Clouds, breaking of a piece of Chalk, stretching a rubber band, cutting a piece of paper, tearing of cloth and rotation of a fan.

Question 57

what are chemical changes?

Answer 57

those changes in which new substances are formed, are called chemical changes. in a chemical change, the substances involved change their identity. the get converted into entirely new substances. the new substances usually cannot be returned to their original form. this means that chemical changes are usualy irreversible. some common examples are: rusting of iron, burning of a magnesium wire, burning of paper, formation of curd from milk, cooking of food.

1. When a magnesium wire is heated, it burns in air to form a white powder called magnesium oxide. this magnesium oxide is an entirely new substance. thus, a new chemical substance is formed during the burning of a magnesium metal wire. so, the burning of magnesium wire is a chemical change.
2. If we burn a piece of paper then an entirely new substance like carbon dioxide, water vapour, smoke and ash are produced.

Chemical changes are permanent changes which are usually irreversible. For example, the burning of paper is a permanent change and it cannot be reversed. some more examples are burning of candle wax, burning of charcoal, burning of fuels, burning of hydrogen and oxygen to form water, decomposition of water into hydrogen and oxygen by passing an electric current ( electrolysis of water ), burning of an incense stick, formation of iron sulphide from iron and sulphur, growth of a plant, cutting of trees, digestion of food.

Question 58

what is the difference between chemical and physical change?

Answer 58

PHYSICAL CHANGE:
1. No new substance is formed.
2. Temporary change
3. Easily reversible.
4. very little heat or light energy is usually absorbed or given out
5. the mass of the substance does not alter

CHEMICAL CHANGE:
1. new substance is formed
2. permanent change
3. usualy irreversible
4. lot of heat or light energy is absorbed or given out
5. mass of a substance does alter

Question 59

explain the seperation of mixtures.

Answer 59

Many of the materials around us are mixtures. These mixtures have two or more than two substances mixed in them. It may not be possible to use a mixture as such in home and industries. We may require only one or two separate constituents of a mixture for our use. So, we have to separate the various mixtures into their individual constituents to make them useful in our daily life.
The various constituents of a mixture have different physical properties such as density, solubility, size of particles, behaviour towards magnets, volatility, boiling points, etc. this difference in the physical properties of constituents is used to seperate them from a mixture.
The method to be used for separating a mixture depends on the nature of its constituents. different mixtures are separated by using different physical processes. The various physical processes which are commonly used to separate the constituents of mixtures are: sublimation, magnet, solvents, filtration, centrifugation, evaporation, crystallisation, chromatography, distillation, fractional distillation and seperating funnel.

Question 60

explain how we can seperate the mixtures containing two solid substances.

Answer 60

All the mixtures containing two solid substances can be separated by one of the following methods:
1. by using a suitable solvent.
2. by the process of sublimation.
3. by using a magnet.

Question 61

Explain the separation of mixture of two solid by a suitable solvent with examples.

Answer 61

In some cases, one constituent of a mixture is soluble in a particular liquid solvent whereas the other constituent is insoluble in it. this difference in the solubilities of the constituents of a mixture can be used to seperate them. for example, sugar is soluble in water whereas sand is insoluble in it, so a mixture of sugar and sand can be seperated by using water as a solvent.

to seperate a mixture of sugar and sand.
sugar is soluble in water whereas sand is soluble in water. the difference in the solubilities of sugar and sand in water is used to seperate them. the mixture of sand and sugar is taken in a beaker and water is added to it. the mixture is stirred to dissolve the sugar in water. the sand remains undissolved. the sugar solution containing sand is filtered by pouring over a filter paper kept in a funnel. sand remains as a residue on the filter paper and sugar solution is obtained as a filtrate in the beaker kept below the funnel. the sugar solution is evaporated carefully to get the crystals of sugar.
a mixture of common salt ( sodium chloride ), and sand can also be seperated by using water as a solvent. this will be similar to the seperation of sugar and sand mixture. copper sulphate, ammonium chloride, potassium nitrate and potash alum are also soluble in water, but carbon and sulphur are insoluble in water. sugar is soluble in alcohol but salt is insoluble in alcohol, so a mixture of sugar and salt can be seperated by using alcohol as a solvent.

to seperate a mixture of sulphur and sand.
sulphur is insoluble in water and sand is also insoluble in water, so water cannot be used as a solvent. sulphur, is however soluble in carbon disulphide, whereas sand is insoluble in it. therefore, a mixture of sulphur and sand can be seperated by using carbon disulphide as solvent. the mixture of sulphur and sand is shaken with carbon disulphide. sulphur dissolves in carbon disulphide whereas sand remains undissolved. the sulphur solution containing sand is filtered when sand is obtained as a residue on the filter paper and sulphur solution is obtained as a filtrate. on evaporating the filtrate, carbon disulphide solvent is eliminated and solid sulphur remains undisturbed.
salt, sugar and carbon are also insoluble in carbon disulphide. so, they can be seperated from sulphur by using carbon disulphide as solvent.

Question 62

explain the seperation of mixture of two solids by sublimation.

Answer 62

The changing of solid directly into vapours on heating and of vapours into solid on cooling, is called sublimation. The solid substance obtained by cooling the vapour is known as sublimate. the substances like ammonium chloride, iodine, camphor, naphthalene and anthracene sublime on heating, and from vapours to solid on cooling.
most of the solid substances do not undergo sublimation. for example, substances such as common salt, sand, iron filings, sulphur, and chalk etc. do not sublime on heating. the process of sublimation is used to seperate the component of a solid-solid mixture which sublime on heating. ( the other component of the mixture being non volatile. ) thus, ammonium chloride, iodine, camphor, naphthalene and anthracene can be seperated from a mixture by sublimation.

Question 63

how to seperate a mixture of common salt and ammonium chloride.

Answer 63

ammonium chloride sublimes on heating whereas common salt does not. so, we can seperate ammonium chloride from a mixture of common salt and ammonium chloride by the process of sublimation. the mixture of common salt and ammonium chloride is taken in a china dish and placed on a tripod stand. the china dish is covered with an inverted glass funnel. a loose cotton plug is put in the upper, open end of the funnel to prevent the ammonium vapours from escaping into the atmosphere. the china dish is heated by using a burner. on heating the mixture, ammonium chloride changes into white vapours. the vapours rise up and get converted into solid ammonium chloride on comming in contact with the cold inner walls of the funnel. in this way, pure ammonium chloride collects on the inner side of the funnel in the form of a sublimate and can be removed. common salt does not change into vapours on heating, so it remains in the china dish. thus, the mixture has been seperated. ammonium chloride, iodine, camphor, naphthalene, and anthracene can be seperated from non volatile like common salt, sand, iron filings, chalk, etc. by the process of sublimation.

Question 64

explain the seperation of mixtures of two solids by a magnet.

Answer 64

iron is attracted by a magnet. This property of iron is used to separate it from a mixture. so, if a mixture contains iron as one of the constituents, it can be separated by using a magnet. For example, a mixture of iron filings and sulphur powder can be separated by using a magnet. This is because iron filings are attracted by a magnet, but sulphur is not.

Question 65

explain how to seperate a mixture of iron filings and the seperation of scrap iron by magnets.

Answer 65

to seperate a mixture of iron filings and sulphur powder:
In order to separate iron filings from sulphur powder, a horse shoe type magnet is moved on the surface of the mixture. The iron filings are attracted by the magnet, they cling to the poles of the magnet and get separated. This process has to be repeated a number of times to achieve complete separation of iron filings. A mixture of iron filings and carbon powder can be separated by using a magnet in a similar way. A mixture of iron filings and sand can also be separated by using a magnet. A carpenter can also separate iron nails from sawdust by using a magnet. This is because iron nails stick to the magnet but sawdust does not. In industries, the impurity of iron present in various substances is removed by the use of magnets.

seperation of scrap iron:
Waste materials supplied to factories contain a number of scrap metals including iron. so, in factories, scrap iron is separated from the heap of waste materials by using big electromagnets fitted to a crane. ( a magnet which works with an electric current is called an electromagnet. ) when a crane fitted with a powerful electromagnet lowered on to the heap of waste materials, then the scrap iron objects present in the heap cling to the electromagnet. the crane is then moved up and away to drop these scrap iron objects at a seperate place. in this way, scrap iron is seperated from the heap of waste materials.

Question 66

explain the seperation of mixture of a solid and a liquid.

Answer 66

1. by filtration.
2. by centrifugation.
3. by evaporation.
4. by crystallisation.
5. by chromatography
6. by distillation.

Question 67

what is filter paper? explain the folding of filter paper.

Answer 67

a filter paper is a round piece of special paper which has millions of tiny holes in it. the holes of a filter paper are so small that they cannot be seen with the naked eyes. they can be seen only with a microscope. the liquids like water, salt solution, oil, etc. can pass through the tiny holes of a filter paper but solid particles such as chalk particles or sand particles being large, cannot pass through the tiny holes of the filter paper. the solid which remains on the filter paper is called residue. the liquid which passes through the filter paper is called filtrate.
folding a filter paper:
Before a filter paper can be used for the process of filtration, it is folded properly to make a hollow cone, which is then kept in the funnel. The filter paper is folded in the following steps:
1. The round piece of filter paper is taken and folded in half.
2. The half folded filter paper is folded again.
3. The twice folded filter paper is open to form a hollow cone by keeping 3 layers of filter paper on one side and one layer on the other side.
4. This cone of filter paper is placed inside a funnel and it is then used for the process of filtration in a science laboratory.

Question 68

explain the seperation of mixture of a solid and a liquid by filtration.

Answer 68

The process of removing insoluble solids from a liquid by using a filter paper is known as filtration. Filtration is used for separating insoluble substances from a liquid. The mixture of insoluble solid and the liquid is poured into a filter paper cone fixed in a funnel by using a glass rod as a guide. The liquid passes through the filter paper and collects in the beaker kept below the funnel. The solid particles, being bigger in size do not pass through the filter paper and remain behind on the filter paper. The solid substance left behind on the filter paper is called residue. The clear liquid obtained is called filtrate. In this way, a mixture of insoluble solid in a liquid is separated into the solid and the clear liquid.
A mixture of chalk and water is separated by filtration. When the mixture of chalk and water is poured on the filter paper fixed in a funnel, then clear water passes through the filter paper and collects as filtrate. the chalk particles remain behind on the filter paper as residue. a mixture of sand and water can also be seperated by filtration.
the “chalk and water mixture” and the “sand and water mixture” which have been seperated by filtration are heterogenous mixtures of a solid in a liquid. this means that a heterogenous mixture of a solid and a liquid can be seperated by the process of filtration. filtration can seperate ONLY insoluble/undissolved substances. filtration cannot remove any solid substances that have dissolved in a liquid.
In science experiments, we use a filter paper as a “filter” for carrying out the process of filtration. For example, wire mesh, a piece of cotton, a piece of fine cloth, or even a layer of sand can be used as filters for various purposes. The size of holes of the filter to be used depends on the size of the solid particles to be separated from the liquid. When we make tea, we add tea leaves. Now, to separate used tea leaves, we pour the prepared tea over a tea strainer. The tea stainer has a wire mesh in it which acts as a filter. The liquid tea passes through the small holes of a tea strainer and collects in the cup below. The tea leaves do not pass through the wire mesh and remain behind on the tea strainer. In this way, the used tea leaves are separated from the prepared tea by the method of filtration.
In many homes, drinking water is filtered by using special water filters which remove bacteria present in it. In cities, gutter water is filtered through big metallic filters to prepare solid materials present in it so as to avoid choking of underground drains. ( called sewers )
the process of filtration plays an important role in the purification of water at water works with supplies drinking water in a city.

Question 69

explain the supply or drinking water in a city with reference to filtration.

Answer 69

in cities, drinking water is supplied from water work. in water works, the methods like sedimentation, decantation, loading, filtration and chlorination, etc. are used to remove undesirable materials from water. The source of water supply in a city is either a nearby river or a lake ( called a reservoir. ) the river water and the lake water usually contain solid substances and some germs. so, before this water can be supplied to our homes, it must be purified to remove suspended impurities as well as germs. This is done at a place called water works. The water works of a city is usually situated near the bank of a river or lake.
The purification of river water or Lake water is done in the following steps:
1. the water from a river or lake is pumped by the pumping station into a large reservoir called sedimentation tank. this water is allowed to stand in the sedimentation tank for sometime. During this time, many of the insoluble substances present in water settle down at the bottom of the tank.
2. from the sedimentation tank, water is sent to a loading tank. In the loading tank, some alum is added to water. the heavy particles of dissolved alum deposit on the suspended clay particles in water. In this way, the suspended clay particles in water get loaded with alum particles, become heavy and settle down at the bottom of the tank. thus, the process of loading by using alum removes the suspended clay particles from the water.
3. the water is then passed through a filtration tank. the filtration tank has three layers: fine sand layer at the top, coarse sand layer in the middle and gravel/tiny stones as the bottom layer. the layers of sand and gravel act as filters. when water passes through the layers of sand and gravel, even the small suspended particles and other materials in water get removed.
4. the clear water is then past into a chlorination tank. a little chlorine gas is added to water in this tank. chlorine is added to water to kill the germs present in it. this is called disinfecting the water or sterilising the water. the water now become fit for drinking.
5. the clean and disinfected water is then pumped by a pumping station into high storage tanks. from the high storage tank, water is supplied to homes and factories in the entire city through a network of big and small pipes

Question 70

explain the seperation of a mixture of a solid and a liquid by centrifugation.

Answer 70

if we have a mixture of fine suspended particles in a liquid, we can seperate it by the process of filtration by using a filter paper. this process is however, very slow. but we can seperate the suspended particles of a substance in a liquid very rapidly by using the method of centrifugation. centrifugation is done by using a machine called centrifuge. we can now say that centrifugation is a method for seperating the suspended particles of a substance from a liquid in which the mixture is rotated or spun at a high speed in a centrifuge.
In the method of centrifugation, the mixture of fine suspended particles in liquid is taken in a test tube. The test tube is placed in a centrifuge machine and rotated rapidly for sometime. As the mixture rotates around rapidly, a force acts on the heavier suspended particles in it and brings them down to the bottom of the test tube. The clear liquid, being lighter, remains on the top. We can separate the clay particles suspended in water very rapidly by the method of centrifugation. This suspension of clay particles in water is taken in a test tube and rotated very fast in a centrifuge machine. The clay particles settle down at the bottom and clear water remains at the top.

Question 71

what is a centrifuge?

Answer 71

a centrifuge is used to separate suspended solid particles from a liquid, quickly. When the centrifuge is switched on, the test tube containing the suspension held in it swing out and spin or rotate at a high speed. The centrifugal force acts on suspended particles which forces them to go to the bottom of test tubes and clear liquid remains on top.

Question 72

explain the separation of cream from milk with reference to centrifugation.

Answer 72

Milk is a suspension of tiny droplets of oil/cream in a watery liquid. The process of centrifugation is used in dairies to separate cream from milk. The milk is put in a closed container in a big centrifuge machine. When the centrifuge machine is switched on, the milk is rotated at a very high speed in its container. Due to this, the milk separates into cream and skimmed milk. The cream, being lighter, floats over the skimmed milk. It can be removed. thus, cream is separated from milk by centrifugation. The process of centrifugation is also used in washing machines the squeeze out water from wet clothes and make them dry.
The methods of filtration and centrifugation can be used to separate an insoluble solid substance from a liquid and they cannot separate a dissolved solid from a liquid. The separation of dissolved solid from a liquid can be done by evaporation, crystallisation, chromatography, and distillation.