Principles of Chemistry Flashcards
What are the three states of matter?
solids
liquids gases
Which state of matter of a material is depends on …
This depends on three things: …
Which state of matter of a material is depends on how strong the forces of attraction are between the particles of the material
This depends on three things:
1. the material
2. the temperature
3. the pressure
In solids, there are strong/weak forces of attraction between the particles.
What do these forces do?
In solids, there are strong forces of attraction between the particles which holds them close together in fixed positions to form a very regular lattice arrangement
In a solid, do the particles move? What does this do to their shape and volume?
the particles don’t move from their positions, so all solids keep a definite shape and volume
The particles in a solid … about their positions - the cooler/hotter the solid becomes, the more they vibrate.
What does this cause them to do?
The particles in a solid vibrate about their positions - thehotter the solid becomes, the more they vibrate (causing solids to expand slightly when heated)
In liquids, there is a strong/weak force of attraction between the particles. They’re arranged … and are/aren’t free to move, but they do/don’t tend to stick closely together
In liquids, there is a weak forxe of attraction between the particles. They’re arranged randomly and are free to move, but they do tend to stick closely together
Liquids do/don’t have a definite volume but do/don’t keep a definite shape, and will/won’t flow to fill the bottom of a container
Liquids do have a definite volume but don’t keep a definite shape, and will flow to fill the bottom of a container
In liquids, do the particles move? What happens when the liquid gets hotter?
the particles are constantly moving with random motion
the hotter the liquid gets, the faster they move - this causes liquids to expand slightly when heated
In gases, the force of attraction between the particles is very strong/weak - they are/aren’t free to move and are/aren’t far apart. The particles in gases travel in straight/curved lines
In gases, the force of attraction between the particles is very weak - they are free to move and are far apart. The particles in gases travel in straight lines
Gases do/don’t keep a definite shape or volume and will always/never fill any container
Gases don’t keep a definite shape or volume and will always fill any container
Do the particles in a gas move? What happens when the gas gets hotter?
the particles move constantly with random motion
the hotter the gas gets, the faster they move
gases either expand when heated, or their pressure increases
What do physical changes do to material?
physical changes don’t change the particles - just their arrangement or their energy
What happens as as a solid is heated? (talk about it changing into a ilquid and then into a gas)
- When a solid is heated, its particles gain more energy
- This makes the particles vibrate more, which weakens the forces that hold the solid together. This makes the solid expand
- At a certain temperature, the particles have enough energy to break free from their positions. This is called melting and the solid turns into a liquid
- When a liquid is heated, again the particles get even more energy
- This energy makes the particles move faster, which weakens and breaks the bonds holding the liquid together
- At a certain temperature, the particles have enough energy to break their bonds. This is called evaporating and the liquid turns into a gas
How does a solid turn into a liquid? Is heat energy being supplied or given out?
melting
heat energy is supplies
How does a liquid turn into a gas? Is heat energy being supplied or given out?
evaporating
heat energy is supplied
How does a gas turn into a liquid? Is heat energy being supplied or given out?
condensing
heat energy is being given out
How does a liquid turn into a solid? Is heat energy being supplied or given out?
freezing
heat energy is given out
How does a solid turn into a gas? Is heat energy being supplied or given out?
subliming
heat energy is supplies
What is diffusion?
diffusion is the gradual movement of particles from areas of high concentration of particles to areas of low concentration of particles
Where is the nucleus in the atom? What does it contain? What is its charge?
the nucleus is in the middle of the atom
it conatins protons and neutrons
it has a positive charge because of the protons
Almost the whole mass of the atom is concentrated in the …
Almost the whole mass of the atom is concentrated in the nucleus
Where do the electrons move?
the electrons move around the nucleus in energy levels called shells
Are electrons negatively or positively charged?
electrons are negatively charges
What does the size of the electrons’ orbit determine?
the size of their orbits determine how big the atom is
Are protons negatively or positively charged?
protons are positively charged
What charge do neutrons have?
neutrons are neutral
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
1/2000
Neutral atoms do/don’t have an overall charge
Neutral atoms don’t have an overall charge
The number of electrons equals/doesn’t equal the number of protons in a neutral atom
The number of electrons equals the number of protons in a neutral atom
What is an ion?
a charged particle
What does the atomic number tell you?
how many protons there are
Atoms of the same element have the … number of protons - so atoms of different elements have … numbers of protons
Atoms of the same element have the same number of protons - so atoms of different elements have different numbers of protons
How do you work out the number of neutrons of an atom?
the mass number (number on top) - the atomic number (number on bottom)
What are molecules and how are they held together?
atoms join together to form molecules
molecules can be made from just one element (e.g. H2), while other are made up of more than one element (e.g. H2O)
molecules are held together by covalent bonds
Elements consist of one/more than one type of atom
Elements consist of one type of atom only
What is a compound?
a substance that is made up of two or more different elements which are chemically bonded together
It is very easy/difficult to separate the two original elemnts out again from a compound
It is very difficult to separate the two original elemnts out again from a compound
Are there chemical bonds between different parts of a mixture? Are mictures easily separated?
there is no chemical bond between the different parts of a mixture
the parts can be separated easily by physical methods
What determines the properties of a mixture?
the properties of a mixture are just a mixture of the properties of the separate parts
When is filtration used?
filtration is used to separate an insoluble solid from a liquid
it can also be used in purification as well - e.g. solid impurities in the reaction mixture can be separated out using filtration
When is crystallisation used?
crystallisation is used to separate a soluble solid from a soultion
How do you crystallise a product?
- Pour the solution into an evaporating dish
- Slowly heat the solution. Some of the solvent will evaporate and the solution will get more concentrated. Stop heating when crystals start to form
- Remove the dish from the heat and leave it in a warm place for the rest of the solvent to slowly evaporate - this way you get nice big crystals
- Finally, you’ve got to dry the product - you can use a drying oven or a desiccator for this (a desiccator contains chemicals that remove water form the surroundings)
How do you separate rock salt
filtration and crystallisation
- Grinding: grind up the rock salt with a pestle and mortar
- Dissolving: dissolve in beaker and stir
- Filtering: filter through fitler paper in a funnel
- Crystallisation: evaporate in an evaporating dish
How do you do paper chromatography?
- Draw a line near the bottom of a sheet of filter paper (use a pencil to do this - pencil marks are insoluble and won’t react with the solvent)
- Add spots of different dyes to the line at regular intervals
- Loosely roll the sheet up and put it in a beaker of solvent, e.g. the water
- The solvent used depends on what’s being tested. Some compounds dissolve well in water, but sometimes other solvents, like ethanol, are needed
- Make sure the dyes aren’t touching the solvent - you won’t want them to dissolve into it
- Place the id on top of the container to stop the solvent evaporating
- The solvent seeps up the paper at a different rate and forms a spot in a different place
- Each different dye will move up the paper at a different rate and form a spot in a different place
- The end result is a pattern of spots called a chromatogram
How does chromatography separate mixtures?
- chromatography works because different dyes will move up the paper at different rate
- some will stick to the paper and other will dissolve more rapidly in the solvent and travel more quickly
- the distance the dyes travel up the paper depends on the solvent and the paper you use
How can chromatography help you idenity dyes?
- If you want to work out what dyes are present in an unknown substance (e.g. an ink), you can use chromatography to find out
- First make chromatograms for your unknown substance and for some reference materials (dyes that you think might be the ink)
- Now compare the chromatograms to work out what dyes are in your unknwocn substance - spots on the chromatogram for the unknown substance will match spots on the chromatograms on the reference materials
What are two used of chromatography?
identifying unknown substances for crime scenes
identifying inks used to print forged money
What are the two types of distillation?
simple distillation
fractional distillation
What is simple distillation used to separate?
simple distillation is used to separate out solutions
How does simple distillation work?
- The solution is heated. The part of the solution that has the lowest boiling point evaporates
- The vapour is then cooled, condenses (turns back into a liquid) and is collected
- The rest of the solution is left behind in the flask
What happens in the simple distillation of sea water?
you can use simple distillation to get pure water from sea water
the water evaporates and is condensed and collected
evetually, you end up with just the salt left in the flask
What is fractional distillation used to separate?
fractional distillation is used to separate a mixture of liquids
How does fractional distillation work?
- You put your micture in a flask and stcik a fractionating column on top. Then you heat it
- The different liquids will all have different boiling points - so they will evaporate at different temperatures
- The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column
- Liquids with higher boiling points might also start to evaporate. So they will only get part of the way up before condensing and running back down towards the flask
- When the first liquid has been collected, you raise the temperature until the next one reaches the top
The elements in any one group in the periodic table have the … number of electrons in their outer shell. What does this do to their properties?
The elements in any one group in the periodic table have the same number of electrons in their outer shell
That’s why they have similar properties
WHat does the properties of the elements in the periodic table depend on?
the number of electrons they have
the atomic number is therefore very significant because it is equal to the number of electrons each atom has
Why do most atoms want to react?
their outer shell is not full of electrons - it wants it be full
What happens in ionic bonding?
in ionic bonding, atoms lose or gain electrons to form charged particles (called ions) which are then strongly attracted to one another (because of opposite charges attract) - this strong attraction is called electrostatic attraction
Ionic compounds have high/low meting and boiling points
Ionic compounds have high meting and boiling points
Which groups most readily form ions?
Groups 1, 2, 6 and 7
Groups 1 and 2 elements are metals/non-metals and they lose/gain electrons to form positive/negative ions (anions/cations)
Groups 1 and 2 elements are metals and they lose electrons to form positive ions (cations)
Groups 6 and 7 elements are metals/non-metals and they lose/gain electrons to form positive/negative ions (anions/cations)
Groups 6 and 7 elements are non-metals and they gain electrons to form negative ions (anions)
What is formed when cations and anions meet up?
ionic compounds
How is ionic bonding represented?
‘dot and cross’ diagrams
Draw the dot and cross diagram for sodium chloride (NaCl)
Draw the dot and cross diagram for magnesium oxide (MgO)
Draw the dot and cross diagram for sodium oxide (Na2O)
Draw the dot and cross diagram for calcium chloride (CaCl2)
What structures do ionic compounds form?
compounds with ionic bonding form giant ionic structures
Explain how ions are held together in a giant ionic structure and how this affects their melting and boiling points
the ions are held together ina closely packed 3D lattice arrangement by the attraction between oppsoitely charged ions
the electrostatic attraction between oppossitely charged ions is very strong - because a lot of energy is needed to overcome the strong attractiom, this means that ionic compounds have high melting and boiling points
A giant ionic lattice of 2+ and 2- ions will be held together by stronger/weaker attractions than a lattice of 1+ and 1- ions. What does this mean for their melting and boiling points?
A giant ionic lattice of 2+ and 2- ions will be held together by stronger attractions than a lattice of 1+ and 1- ions
this means that lattices made up of higher charged ions will have higher melting and boiling points
Sodium chloride has a typical ionic structure. Draw this structure
What is covalent bonding?
atoms bonding tgether by sharing a pair of electrons to make covalent bonds
in covalent bonding, there is a strong attraction between the shared electrons (the bonding pair) and the nuclei of the atoms involved
How is covalent bonding represented?
dot and cross diagrams
Draw the dot and cross diagram for hydrogen, H2, and Chlorine, Cl2
they form single covalent bonds
Draw the dot and cross diagram for hydrogen chloride, HCl
it forms a single covalent bond
Draw the dot and cross diagram for ammonia, NH3
it forms single covalent bonds
Draw the dot and cross diagram for nitrogen, N2
it forms a triple covalent bond
Draw the dot and cross diagram for water, H2O, oxygen, O2, and carbon dioxide, CO2
water forms single covalent bonds
oxygen and carbon dioxide form double covalent bonds
Draw the dot and cross diagram for methane, CH4
it forms single covalent bonds
Draw the dot and cross diagram for ethane, C2H6
they form single covalent bonds
Draw the dot and cross diagram for ethene, C2H4
the carbon atoms form double covalent bonds
the hydrogen and carbon atoms form single covalent bonds
What do structures can substances containing covalent bonds be?
simple molecular structures
giant covalent structures
In simple molecular substances, the atoms within a molecule are held together by very strong/weak covalent bonds. By contrast, the forces of attraction between the molecules are very strong/weak
In simple molecular substances, the atoms within a molecule are held together by very strong covalent bonds. By contrast, the forces of attraction between the molecules are very weak
Simple molecular substances have very high/low melting and boiling points. Why?
Simple molecular substances have very low melting and boiling points because of the weak intermolecular forces between the molecules which are easily parted from each other
What state of matter are most simple molecular substances at room temperature? How can you usually tell a molecular substance from its physical state?
most simple molecular substances are gases or liquids at room temperature
you can usually tell a molecular substance from its physical state, which is always ‘mushy’ - i.e. liquid, gas or an easily melted solid
In a giant covalent structure, how are all the atoms bonded? What does this mean for their melting and boiling points?
in a giant covalent structure, all the atoms are bonded to each other by strong covalent bonds
there are lots of these bonds which means it takes a lot of energy to break them, so they have very high melting and boiling points
Do giant covalent structures conduct electricity? What is the exception?
giant covalent structures don’t conduct electricity - not even when molten (except for graphite)
Giant covalent strctures are soluble/insoluble in water
Giant covalent strctures are insoluble in water
Explain the structure of diamond. Is it hard or soft? What are two of its uses?
in diamond, each carbon atom forms four covalent bonds in a rigid giant covalent structure
this structure makes diamond the hardest natural substance, so it’s used for drill tips and tools
Explain the structure of graphite. Can it conduct electricity? Why? What is one of its uses?
in graphite, each carbon atom only forms three covalent bonds, creating layers which are free to slide over each other
this makes grpahite useful as a lubricant
it also leaves free electrons, so graphite is the only non-metal which is a good conductor of electricity
What atoms are both diamond and graphitee made up of?
diamond and graphite are made only from carbon atoms
What is an isotope?
isotopes are different atomic forms of the same element, which have the same nuber of protons but different numbers of neutrons
What changes if the proton number changes?
the elements altogether
What is relative atomic mass?
how heavy different atoms are compared with the mass of an atom of carbon-12
What is relative abundance?
how much there is of each isotope compared to the totals amount of the element in the world
this cn be a ratio, a fraction or a percentage
What is relative formula mass?
the relative atomic masses of the a compound added together
What is the empirical formula?
the empirical formula of a compound is the simplest formula that tells you the ratio of different elements in the compound
Work out the empirical formula of iron oxide
mass of iron = 44.8
mass of oxygen = 19.2
Ar of iron = 56
Ar of oxygen = 16
1. List all the elements in the compound
Fe : O
2. Underneath them, write their experimental masses or percentages
44.8 : 19.2
3. Divide each mass or percentage by the Ar for that particular element
(44. 8 ÷ 56) : (19.2 ÷ 16)
0. 8 : 1.2
4. Turn the numbers into a nice, simple ration by multiplying and/or dividing them by well-chosen numbers
(multiply by 10) 8 : 12
(then divide by four) 2 : 3
5. Give the ration in its simplest form
Fe2O3
What is the molecular formula?
the molecular formula of a compound tells you the actual number of atoms of each element in a single molecule
A molecule has an empirical formula of C4H3O2, and a relative molecular mass of 166. Work out its molecular formula
1. Find the mass of the empirical formula
(4 x 12) + (3 x 1) + (2 x 16) = 83g
2. Divide the relative molecular mass by the empirical formula mass
166 ÷ 83 = 2 empirical units in the molecule
3. Multiply the empirical formula by the empirical units in the molecule
C4H3O2 x 2
= C8H6O4
How do you work out the percentage yield?
percentage yield = actual yield (grams) ÷ theoretical yiels (grams) x 100
What is a moles? (i.e. the number)
6.023 x1023
How much does one mole of carbon weigh?
(Ar = 12)
12g
How much does one mole of nitrogen gas, N2, weigh?
(Ar = 14)
(2 x 14)
= 28 g
Whatis Avogadro’s number?
6.023 x1023
What is the equation to find the number of moles of any given mass?
number of moles = mass in g ÷ Mr
What do all solids consist of?
all solids consist of a lattice of positive and negative ions
What is water of crystallisation?
some salts are hydrated - their lattices contain water molecules as well as positive and negative ions
the water in the lattice is called water of crystallisation
What is an anhyrdous salt?
a salt that doesn’t contain ant water of crystallisation - no water molecules in their lattice
What happens when many hydrated salts are heated?
many hydrated salts lose their water of crystallisation when heates to become anhydrous
Heating hydrated magnesium sulphate, MgSO4 • xH2O, in a crucible forms anhydrous magnesium sulphate, MgSO4. Use the experimental data below to find the value of X and write the formula of the hydrated salt
Mass of empty crucible = 42.000g
Mass of crucible + MgSO4 • xH2O = 45.210g
Mass of crucible + MgSO4 = 43.567g
1. Calculate the mass of MgSO4 • xH2O and MgSO4 you have
mass of MgSO4 • xH2O = 45.210 - 42.000 = 3.210
mass of MgSO4 = 43.567 - 42.000 = 1.567
2. Calculate the number of moles of water lost
mass of water lost: 3.210 - 1.567 = 1.643
number of moles of water lost = mass ÷ Mr
= 1.643 ÷ ((2 x 1) + 16)
= 0.0913
3. Calculate the number of moles of anhydrous salt made
molar mass of MgSO4 = (24 + 32 + (4 x 16)) = 120g/mol
number of moles MgSO4 = mass ÷ Mr
= 1.567 ÷ 120
= 0.0131 moles
4. Calculate the ratio of moles of anhydrous salt to moles of water
0.0131 moles of salt : 0.0913 moles of water
1 mole of salt = (0.0913 ÷ 0.0131)
= 6.97 moles of water
5. x must be a whole nymbers so round upwards
x = 7
MgSO4 • 7H2O
How much does one mole of any gas occupy?
one mole of any gas always occupies 24 dm3 (= 24,000 cm3) at room temperature (25oC) and pressure (1 atmopshere)
1 mole of gas = 24 dm3 / 24,000 cm3
What is the molar volume?
the spa e that one mole of gas takes up
Whar ae the two formulas for volume (dm3)
volume (dm3) = moles of gas x 24
volume (dm3) = (mass of gas ÷ Mr of gas) x 24
What is the concentration of a solution and what is it usually measured in?
concentration is the ‘amount of stuff’ per unit volume
it is usually measured in moles per dm3 (i.e. moles per litre)
What is the concentration of 1 mole of stuff in 1 dm3?
1 mole per dm3 (1 mol/dm3)
What is the equation for the concentration of a solution?
concentration (in mol/dm3) = number of moles ÷ volume (in dm3)
How many dm3 are in a litre?
one dm3 = one litre
How do you convert moles per dm3 to grams per dm3?
divide the mass of the chemical in grams by the volume you used to dissolve it in dm3
What can electrons and ions act as in terms of electricty?
electrons and ions can act as charge carriers - they can move charge around a system to create a flow of electricity
What is an electric current?
the flow of electrons or ions
When does an ionic compound conduct electricity?
ionic compounds only conduct electricity when molten or in solution
solid ionic compounds don’t conduct electricity because the ions aren’t free to move around - they are in a lattice
when ionic compound is dissolved, the ions separate and are free to move in the colution - this means they will carry and electrict current and so conduct electricity
when ionic compound melts, the ions are free to move and will carry electric current
Do covalent compounds conduct electricity? Why?
covalent compounds don’t conduct electricty
covalent compounds don’t contain ions becase they make bonds by sharing electrons
this means they don’t have any charge carriers that are free to move - so they can’t carry an electric current
How are metals held together?
metals are held together by metallic bonding
metals have a giant structure of positive ins surrounded by a sea of delocalised (free) electrons
the attraction between the positive ions and the electrons is called metalic bonding
this metallic bonding gives metals their properties
Metals are good/poor conductors of heat and electricity. Why?
Metals are good conductors of heat and electricity
the delocalised electrons carry electrical current and heat energy through the material, so metals are good conductors of electricity and heat
Most metals are/aren’t malleable. Why? What does malleable mean?
Most metals are malleable
malleable = able to be hammered or rolled into shape
this is because the layers of atoms in a metal can slide over each other
Reliable results come from experiments that give … data
Reliable results come from experiments that give the same data
What are valid results?
valid results are both reliable and come from experiments that were designed to be a fair test
How do you improve the validity of an experiment?
control variable improves validity
How do you improve the reliability of an experiment?
repeat any measurement you make at least three times and calculate the mean (average)
How would you reduce the risk of acids in an experiment?
always wear gloves and safety goggles
this will reduce the risk of the acid coming into contact with your skin and eyes
How would you reduce the risk of fire in an experiment?
if you’re using a Bunsen burner, stand it on a heat proof mat
this will reduce the risk of starting a fire
How would you reduce the risk of chemicals in an experiment?
if you’re working with chemicals that give off harmful gases, you need to use a fume cupboard
this will reduce the risk of you breathing in the gases
What are accurate result?
results that are very close to the true answer
What are precise results? How do you improve precision?
precise results are those taken using sensitive instruments that measure small increments
by recording your results to a greater number of decimal places, you’ll increase their precision
When calculating an average, do you include any anomalous results?
when calculating an average, ignore any anomalous results
