C3 Flashcards
What is the structural formula of ethanoic acid?
CH3COOH (small 3)
What are the properties of methanol, ethanol and propanol?
They are colourless liquids that dissolve in water to form a neutral solution (pH7).
They react with sodium to produce hydrogen and a salt. For example:
ethanol + sodium → hydrogen + sodium ethoxide
They burn in the air, releasing energy and producing carbon dioxide and water.
What is vinegar?
Vinegar is an aqueous solution containing ethanoic acid.
What properties do esters have in common?
they are volatile - they are liquids that become vapours easily
they have distinctive ‘fruity’ smells
How do you name esters?
The first part of an ester’s name comes from the alcohol - it ends with the letters ‘yl’. The second part of its name comes from the carboxylic acid - it ends with the letters ‘oate’
What are the use of methanol, ethanol and propanol?
These alcohols are highly flammable, making them useful as fuels. They are also used as solvents in marker pens, medicines, and cosmetics (such as deodorants and perfumes). Ethanol is the alcohol found in alcoholic drinks such as wine and beer. Ethanol is usually mixed with petrol for use as a fuel
How is ethanoic acid formed?
Ethanoic acid is formed from the mild oxidation of the ethanol (which is an alcohol). This can be achieved through:
The addition of chemical oxidising agents - such as acidified potassium dichromate. The action of microbes in aerobic conditions (in the presence of oxygen). This happens on a small scale when a bottle of wine is left open and exposed to air. On a commercial scale, it is achieved in a fermenter using acetic acid bacteria.
How do you make Ethyl ethanoate?
Ethyl ethanoate is the ester made from ethanol and ethanoic acid. Sulfuric acid is added to act as a catalyst in the reaction.The distinctive smell of ethyl ethanoate (which is like modelling glue) can be detected as the reaction proceeds. Excess ethanoic acid in the reaction mixture is neutralised with sodium hydrogencarbonate, then a few drops of the mixture added to water so that the smell can be detected more effectively.
What is the structural formula of methanol?
CH3OH (small 3)
What is the structural formula of methanoic acid?
HCOOH
What is the equation for the reaction between ethanol and ethanoic acid?
ethanol + ethanoic acid (double arrow)ethyl ethanoate + water
CH3CH2OH(aq) + CH3COOH(aq) (double arrow) CH3CH2OOCCH3(aq) + H2O(l)
What will weak acids do when dissolved in water?
Carboxylic acids are weak acids. They do not completely ionise when they are dissolved in water. Instead only some of their molecules ionise to form H+ ions:
CH3COOH(aq) Equilibrium symbol CH3COO–(aq) + H+(aq)
This means that an aqueous solution of a weak acid will have a higher pH compared to the same concentration of an aqueous solution of a strong acid.
What are esters?
Esters are a group of organic compounds which all contain the functional group –COO–.
What is the structural formula of propanol?
CH3CH2CH2OH (small numbers)
What are the carboxylic acids?
The carboxylic acids are a homologous series of organic compounds. They all contain the same functional group –COOH.
The names of carboxylic acids end in ‘-oic acid’ – eg ethanoic acid.
What are the uses of esters?
very useful as food flavourings, and as perfumes in cosmetics. Some esters are obtained from natural sources, such as fruits. Others are manufactured.
Why is the reaction of alcohol with sodium similar to the reaction of water with sodium?
This reaction is similar but less vigorous to the reaction of water with sodium. This is due to the similarity in structure between water and the –OH group in alcohols.
What is the structural formula of propanoic acid?
CH3CH2COOH (small numbers)
What are the properties of carboxlic acids?
They dissolve in water to produce acidic solutions (pH less than 7).
They react with carbonates to produce carbon dioxide and a salt and water. For example:
calcium carbonate + ethanoic acid → calcium ethanoate + water + carbon dioxide
They all react with alcohols, in the presence of an acid catalyst, to form esters. For example:
ethanol + ethanoic acid → ethyl ethanoate + water
What will strong acids do when dissolved in water?
Strong acid, such as hydrochloric acid, ionise fully in water:
HCl(aq) → H+(aq) + Cl–(aq)
Their aqueous solutions have a high concentration of hydrogen ions, H+. This gives them a low pH.
What are alcohols?
The alcohols are a homologous series of organic compounds. They all contain the functional group –OH. This group is responsible for the properties of alcohols.
The names of alcohols end with ‘-ol’ – eg ethanol.
What is the structural formula of ethanol?
CH3CH2OH (small numbers)
What are the first three alcohols in the homologous series?
The first three alcohols in the homologous series are methanol, ethanol and propanol.
What happens if the temperature increases in a reversible reaction in a closed system?
If the temperature is increased, the yield from the endothermic reaction increases (and the yield from the exothermic reaction decreases).
What is a closed system?
A closed system is a system in which no reactants are added and no products are removed.
What is the fifth step in the Haber process?
The unreacted hydrogen and nitrogen gases are recycled by being fed back through pipes to pass through the hot iron catalyst beds again.
How is ammonia manufactured?
Ammonia is manufactured by combining nitrogen and hydrogen in an important industrial process called the Haber process.
How do you change the temperature to increase the equilibrium yield of ammonia?
In the Haber process, the forward reaction is exothermic and the backward reaction is endothermic. If the temperature is decreased, the yield from the exothermic direction is increased. (ammonia yield increases)
What is the first step in the Haber process?
Having obtained the hydrogen and nitrogen gases (from natural gas and the air respectively), they are pumped into the compressor through pipes.
In the Haber process, what conditions do hydrogen and nitrogen react under?
a high temperature - about 450°C
a high pressure - about 200 atmospheres (200 times normal pressure)
An iron catalyst is used to increase the rate of reaction.
What is the second step in the Haber process?
The gases are pressurised to about 200 atmospheres of pressure inside the compressor.
What does the percentage yield of ammonia depend on?
The percentage yield of ammonia at equilibrium depends on the balance between the forward and backward reactions.
Show the equation of the reaction between hydrogen and nitrogen?
The reaction between nitrogen and hydrogen is reversible:
nitrogen + hydrogen (double head arrow) ammonia
N2(g) + 3H2(g) (double head arrow) 2NH3(g)
How does equipment affect cost?
An industrial plant is expensive to build and maintain. When high pressures are used - as in the manufacture of ammonia - the cost is particularly high. Reaction vessels have to be very strong and there must be rigorous safety precautions.
What is ammonia?
Ammonia, NH3, is a compound of nitrogen and hydrogen. It is a colourless gas with a choking smell, and a weak alkali that is very soluble in water.
What happens when a reversible reaction happens in a closed system?
When a reversible reaction happens in a closed system, equilibrium is reached in which the rate of the forward reaction is the same as the backward reaction.
For example, the production of ammonia is a reversible reaction:So while nitrogen and hydrogen continually combine to form ammonia, ammonia is continually breaking up to form nitrogen and hydrogen:
What is the third step in the Haber process?
The pressurised gases are pumped into a tank containing beds of iron catalyst at about 450°C. In these conditions, some of the hydrogen and nitrogen will react to form ammonia.
How is hydrogen obtained for ammonia manufacture?
Hydrogen is obtained by reacting natural gas (mostly methane) with steam, or by cracking oil fractions.
What is the compromise which has to be made in the Haber process in terms of temperature?
Therefore, a compromise has to be made between achieving a reasonable rate of reaction and still achieving a reasonable percentage yield of ammonia. The optimum temperature for this compromise is around 450°C.
What is the issue with decreasing temperature?
However, by decreasing the temperature the molecules move more slowly and collide less frequently. This lowers the rate of reaction.
How can labour costs be lowered?
Labour costs can be reduced by automating processes.
What is ammonia used for?
Ammonia is used to make fertilisers (as a source of nitrogen for plants), explosives, dyes, household cleaners and nylon. It is also the most important raw material in the manufacture of nitric acid.
What happens if you increase the pressure in a reversible reaction in a closed system?
If the pressure is increased during reactions involving gases, then the reaction that produces the least number of molecules of gas is favoured.
What does equilibrium mean?
rate of the forward reaction is the same as the backward reaction and the concentrations remain the same.
What is the fourth step in the Haber process?
The unreacted nitrogen and hydrogen, together with the ammonia, pass into a cooling tank. The cooling tank liquefies the ammonia, which can be removed into pressurised storage vessels.
How does energy used affect cost?
The higher the temperature used, the higher the energy cost and the higher the impact on the environment. This impact has economic costs associated with it as companies are charged for the pollution they generate.
What are the different component that make up the cost of a new substance?
energy (gas and electricity) needed
the starting materials equipment(plant) labour (the wages of the people needed)
How is nitrogen obtained for ammonia manufacture?
Nitrogen is obtained from the air. Air is 78 per cent nitrogen; nearly all the rest is oxygen. When hydrogen is burned in air, the oxygen combines with the hydrogen - leaving nitrogen behind.
What is the issue with increasing pressure in the Haber process?
achieving high pressures requires a lot of energy. It also requires stronger pipes and tanks to withstand that pressure. This is costly for companies.
What is the compromise which is made in the Haber process in terms of pressure?
Therefore, a compromise must be made between optimising the amount of product formed, and the cost remaining economically viable. The pressure used is around 200 atmospheres.
What happens if the temperature decreases in a reversible reaction in a closed system?
If the temperature is decreased, the yield from the endothermic reaction decreases (and the yield from the exothermic reaction increases).
What is done to minimize the cost of raw materials?
Unused reactants are recycled to minimise the cost of raw materials.
How do catalysts reduce cost in manufacture of new substances?
The longer a process takes, the more expensive it is likely to be. A large yield produced over a long period of time is more costly and less desirable than a reduced yield produced quickly. Catalysts are therefore often used to speed up reactions.
How do you change pressure to increase the equilibrium yield of ammonia?
There are fewer molecules of gas on the right-hand side of the chemical equation than there are on the left hand side:
N2(g) + 3H2(g) (double headed arrow) 2NH3(g)
If the pressure is increased, the reaction that produces the least number of molecules of gas is favoured. This means that the equilibrium yield of ammonia is increased if the pressure is increased.
How do you test for sulfate ioons?
You can test to see if a solution contains sulfate ions SO42- using barium chloride solution. To do this:
- a few drops of dilute hydrochloric acid are added to the solution
- a few drops of barium chloride solution are then added
The presence of a white precipitate of barium sulfate shows the presence of sulfate ions in the solution.
What does it mean if during a flame test the flame turns lilac?
The metal ion present is potassium.
How can you use precipitation to identify metal ions?
A precipitate may be formed when a few drops of sodium hydroxide are added to a solution of a metal compound.The colour and the properties of the precipitate can be used to identify the metal ion present.
How do you carry out a titration?
A pipette is used to accurately measure a volume of an alkali, often 25 cm3. A pipette filler is used to draw solution into the pipette safely. The alkali is emptied into a conical flask.
A few drops of a suitable indicator are then added to the conical flask.
The acid is placed in a burette and the starting volume of acid is read against the scale marked on the burette.
The acid from the burette is added to the conical flask, and the flask is swirled to mix its contents. When the acid in the burette has almost run in, it is added one drop at a time. Eventually, a colour change shows that the correct amount has been added to react completely with the alkali in the conical flask.
The volume of acid added from the burette is noted. The titration results can then be used to calculate the concentration of the acid or alkali (if the concentration of the other is known).
What indicator is used instead for titrations and what colours does it show when acid or alkali?
Phenolphthalein is often used instead. It changes from pink in alkali to colourless in acid.
What are flame tests used for?
to detect the presence of a particular metal ion in a compound. Metal ions change the colour of a flame when they are heated in it
How do you test for carbonate ions?
Step 1: Carbonates react with dilute acids to produce carbon dioxide and water
Step 2: Collect the gas given off and bubble it through limewater. Limewater is calcium hydroxide solution. It turns cloudy white if carbon dioxide is bubbled through it:
The presence of the white precipitate confirms that carbonate ions were originally present in step 1.
How do you calculate the chemical quantities in titrations involving masses in grams per dm3.
A sample of vinegar contains 0.1 mol/dm3 ethanoic acid. What is its concentration in g/dm3? (The relative formula mass, Mr, of ethanoic acid is 60)
concentration in g/dm3 = concentration in g/dm3 × Mr
concentration = 0.1 × 60 = 6 g/dm3
Answer
6 g/dm3
What does it mean if a yellow precipitate forms when testing for halide ions?
It means Silver iodide, AgI has been produced, and that Iodide, I– were present
How do you work out concentration of a reactant in titration?
Step 1: Convert volumes to dm3 by dividing by 100.
Step 2: Determine the number of moles of the alkali/acid (known concentration)
Step 3: Work out the ratio of moles using a balanced symbol equation.
Step 4: Calculate the concentration of acid/alkali by dividing the numbers of moles by the volume. Give the units in mol/dm3
How can you tell the difference between aluminium ions and the calcium and magnesium ions?
it is possible to identify whether the white precipitate is due to the presence of aluminium ions, as adding excess sodium hydroxide causes a precipitate of aluminium hydroxide to dissolve. This does not happen for the precipitates formed by calcium and magnesium ions.
How would you carry out a flame test?
1.
dip a clean flame test loop in the sample solution
2.
hold the flame test loop at the edge of a Bunsen burner flame
3.
observe the changed colour of the flame, and decide which metal it indicates
4.
clean the loop in acid and rinse with water, then repeat steps 1 to 3 with a new sample
What is the equation for concentration in g/dm3?
concentration in g/dm3 = concentration in g/dm3 × Mr
What does it mean if during a flame test the flame turns green?
The metal ion present is barium.
What does it mean if during a flame test the flame turns crimson?
The metal ion present is Lithium.
What does it mean if white precipitates are formed when reacted with sodium hydroxide?
Calcium, magnesium and aluminium all form white precipitates when reacted with sodium hydroxide.
What are the units for concentration?
mol/dm3
What are titrations used for?
Titrations are used to determine the volumes of acid and alkali needed to react together to produce a neutral solution.
What does it mean if a white precipitate forms when testing for halide ions?
It means Silver chloride, AgCl has been produced, and that Chloride, Cl– ions were present.
What does it mean if a cream precipitate forms when testing for halide ions?
It means Silver bromide, AgBr has been produced, and that Bromide, Br– were present
What is dm3 in cm?
1000 cm3
What is a precipitate?
this is an insoluble solid formed in the reaction.
What do metal carbonates contain?
Metal carbonates contain carbonate ions, CO32-
What does it mean if a brown precipitate forms?
Iron (III)
What is the equation to work out moles?
Moles= concentration x volume
What does it mean if during a flame test the flame turns yellow?
The metal ion present is sodium
What is the chemical reaction for when sodium hydroxide solution is added to copper(II) sulfate solution:
copper(II) sulfate + sodium hydroxide → copper hydroxide + sodium sulfate
CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)
How do you test for halide ions?
You can test to see if a solution contains chloride ions, bromide ions or iodide ions using silver nitrate solution. To do this:
- a few drops of dilute nitric acid are added to the solution
- a few drops of silver nitrate solution are then added
- the colour of any precipitate formed is recorded
Why is universal indicator not suitable for titrations?
Universal indicator is unsuitable for titrations because it has a range of colours and is therefore not exact enough.
What does it mean if a blue precipitate forms?
Copper (II)
What does it mean if a green precipitate forms?
Iron (II)
What happens during an exothermic reaction to the energy and bonds?
In an exothermic reaction, more energy is released when new bonds are made than is needed to break existing bonds.
What is a bond energy?
bond energy is the amount of energy needed to break a mole of a particular bond.
What are the units for energy?
Energy is normally measured in joules, J. However sometimes the amount of energy can be given in other units, including kilojoules, kJ (1 kJ = 1000 J), kJ per mole and kJ per gram.
What are some examples of exothermic reactions?
combustion
neutralisation reactions between acids and alkalis
the reaction between water and calcium oxide
What happens during a chemical reaction?
bonds in the reactants are broken
new bonds are made in the products
Energy is needed to break bonds, and energy is released when bonds are made
What are the advantages of using a catalyst?
Lowering the activation energy has many advantages. It means that reactions happen more quickly and are more economical in terms of the energy required for industrial-scale reactions.
What are the disadvantages of hydrogen production?
At the moment, most hydrogen is made by reacting steam with coal or natural gas - both non-renewable resources.
Hydrogen can also be made by passing electricity through water. Unfortunately, most electricity is generated using coal and other fossil fuels, so pollution from burning these fuels happens at the power station.
What is the main source of error for the calorimetry experiment and how can this be reduced?
The biggest source of error is usually heat loss to the surroundings. This can be reduced by insulating the sides of the calorimeter and adding a lid.
Describe a simple calorimetry experiement?
1.
measure cold water into a calorimeter (a metal or glass container)
2.
record the starting temperature of the water
3.
heat the water using the flame from the burning fuel
4.
record the final temperature of the water
Why is there an initial curve in energy level diagrams?
However, the energy curve goes up from the reactants’ energy level to begin with, then drops to the products’ energy level. This is because many reactions need an input of energy to start the reaction off. This is energy is called the activation energy. It is represented on an energy level diagram as the difference between the reactants’ energy level and the top of the curve
What are the advantages of using hydrogen as a fuel?
unlike petrol and diesel, hydrogen does not generate carbon dioxide when burnt
hydrogen fuel cells are very efficient
What is calorimetry?
The amount of energy transferred during chemical reactions.
What is the specific heat capacity of water?
The specific heat capacity of water is 4.2 J/g°C. This value is also used when the liquid being heated is not water. For example if an acid, alkali or other solution is being used.
How would you perform the experiment to find the energy changes for neutralisation reactions?
1.
add a known volume of the first reactant (in solution) to the insulated container
2.
record the starting temperature of the liquid
3.
add the second reactant (either in solution or as a solid powder)
4.
replace the lid and stir the reaction mixture
5.
record the maximum temperature that the reaction mixture reaches
Knowing the mass of reactant and/or volumes of solution and the temperature change, it is possible to calculate the energy change during the reaction.
What are the two ways of using hydrogen to power cars?
1.Burning hydrogen directly in the engine
Water is the only product formed when hydrogen burns:
hydrogen + oxygen → water
2.Hydrogen fuel cells
In a hydrogen fuel cell, hydrogen reacts with oxygen without burning. The energy released is used to generate electricity, which is used to drive an electric motor.
What does it mean if there is a negative energy change?
The energy change is negative, showing that energy is released to the surroundings in an exothermic reaction.
What happens during an endothermic reaction to the energy and bonds?
In an endothermic reaction, more energy is needed to break existing bonds than is released when new bonds are made.
What is the equation to calculate the energy transferred during a chemical reaction?
Q = mc ΔT
Where:
Q = the heat energy transferred (joule, J)
m = the mass of the liquid being heated (grams, g)
c = the specific heat capacity of the liquid (joule per gram degree Celsius, J/g°C)
ΔT = the change in temperature of the liquid (degree Celsius, °C)
What happens in exothermic reactions?
Exothermic reactions give out heat energy to the surroundings. Exothermic reactions have a negative energy change. This is an energy level diagram by the arrow going down from the products to the reactants.
What else can be done to the spirit burner in the calorimetry experiment?
The spirit burner containing the fuel is usually weighed before and after the experiment - in this way, the mass of the fuel burned can be found. Knowing the mass of fuel burnt and the temperature change in the water, it is then possible to calculate the energy released by the fuel. This method also works for finding the amount of energy released by foods.
What are some examples of an endothermic reaction?
electrolysis
the reaction between ethanoic acid and sodium carbonate
the thermal decomposition of calcium carbonate in a blast furnace
What does it mean if there is a positive energy change?
The energy change is positive, showing that energy is taken in from the surroundings in an endothermic reaction.
What happens in an endothermic reaction?
Endothermic reactions absorb heat energy from the surroundings, making the temperature of the surroundings cooler. Endothermic reactions have a positive energy change. In an energy level diagram this is shown by an arrow going up from the reactants to the products.
How do catalysts increase the rate of reaction?
Catalysts can do this because they provide a different pathway for the reaction to follow. This pathway has lower activation energy than the one followed by the uncatalysed reaction. As a result, a greater proportion of reacting particles have enough energy to react.
What are the disadvantages of using hydrogen as a fuel?
few filling stations sell hydrogen
hydrogen must be compressed and liquefied, and then stored in tough, insulated fuel tanks
atmospheric pollution may be generated during the production of hydrogen
hydrogen fuel cells do not work at very low temperatures, and they may also require a platinum catalyst (platinum is expensive and prone to contamination by impurities)
How do you calculate the energy change using bond energies?
1.
Add together all the bond energies for all the bonds in the reactants – this is the ‘energy in’ (You’ll be given all bond energies in the exam)
2.
Add together the bond energies for all the bonds in the products – this is the ‘energy out’.
3.
Calculate the energy change: energy in – energy out.
What does hard water form with soap?
The dissolved calcium ions and magnesium ions in hard water react with the soap to form scum, so more soap is needed.
What is the disadvantage of distilling seawater in order to produce pure water?
it is expensive because large amounts of energy are needed to heat the seawater
it increases the use of fossil fuels - which are non-renewable resources
carbon dioxide emissions from burning fossil fuels contribute to global warming
What are the advantages of fluoridated water?
Results from scientific research indicate that fluoridated water can improve dental health by reducing tooth decay. Many areas of the country naturally have low fluoride levels present in the water supply.
What do water filter cartridges contain?
silver to kill bacteria
carbon (‘activated charcoal’) to absorb impurities, eg chlorine
ion exchange resins to soften the water, and remove heavy metal ions (such as lead ions)
What is the disadvantage of distilling seawater in order to produce pure water?
it is expensive because large amounts of energy are needed to heat the seawater
it increases the use of fossil fuels - which are non-renewable resources
carbon dioxide emissions from burning fossil fuels contribute to global warming
What happens to the water after the sedimentation tank and why?
Chlorine is added to drinking water to sterilise it. The chlorine kills microbes - including microbes that cause potentially-fatal diseases such as typhoid, cholera and dysentery.
How can you get pure water from seawater?
pure water can be produced from seawater by distillation.
During distillation, the seawater is boiled. The water vapour is then cooled and condensed to form pure water - leaving the salt behind.
What happens to the water next? (sedimentation tank)
The water is then passed into a sedimentation tank. Aluminium sulfate is added to clump tiny particles together to make larger particles, which settle out more easily. The water is then passed through a fine filter, such as carbon granules, to remove very small particles.
What are the advantages of fluoridated water?
Results from scientific research indicate that fluoridated water can improve dental health by reducing tooth decay. Many areas of the country naturally have low fluoride levels present in the water supply.
How can you get pure water from seawater?
pure water can be produced from seawater by distillation.
During distillation, the seawater is boiled. The water vapour is then cooled and condensed to form pure water - leaving the salt behind.
How does adding sodium carbonate to hard water soften it? (use an equation)
Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble.
The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble precipitates. For example:
calcium ions + sodium carbonate → calcium carbonate + sodium ions
Ca2+(aq) + Na2CO3(aq) → CaCO3(s) + 2Na+(aq)
The water is softened because it no longer contains dissolved calcium ions and magnesium ions. It will form lather more easily with soap.
What is the chemical formula of sodium carbonate and what is it also known as?
Sodium carbonate, Na2CO3, is also known as washing soda.
What are the advantages of using ion exchange columns?
Sodium chloride is cheap and widely available, making this a convenient and cost-effective system.
What are the disadvantages of using sodium carbonate to soften hard water?
the calcium carbonate and magnesium carbonate precipitates to form limescale. As well as being unsightly on your taps, it can also clog up pipes in heating systems (causing them to break down). This makes treatment with sodium carbonate suitable for softening water only in certain circumstances - such as softening water for hand washing clothes.
What is a resourvoir?
a reservoir is usually an artificial lake, made by building a dam to accumulate and save river water in the valley behind.
How can you soften hard water?
Methods for softening hard water involve the removal of calcium ions and magnesium ions from the water.
There are two methods for softening hard water:
adding sodium carbonate to the water
using ion exchange columns
What are the arguements agaisnt fluorine being added to water?
has been linked to tooth mottling (staining), bone disease and pain
forces people to consume fluoride when they drink tap water - taking away their personal choice (making it unethical)
What must have to resin beads after softening hard water?
Once the resin beads in dishwashers become saturated with calcium and magnesium ions, they must be regenerated by adding sodium chloride (common salt). The sodium ions it contains replace the calcium and magnesium ions on the beads.
What are ion exchange columns?
Commercial water softeners often use ion exchange resins. These substances are usually made into beads, which are packed into cylinders called ion exchange columns. These can be built into machines, such as dishwashers, or plumbed into water systems to continuously soften the water.
What is an aquifer?
An aquifer is an underground layer of permeable rock, gravel or sand that is soaked with water
What happens to the water next? (sedimentation tank)
The water is then passed into a sedimentation tank. Aluminium sulfate is added to clump tiny particles together to make larger particles, which settle out more easily. The water is then passed through a fine filter, such as carbon granules, to remove very small particles.
What is the order by which water is purified?
Screen, coarse filter, sedimentation tank, Fine filter, chrlorine added, then into a storage tanks, and then into homes and factories.
How does adding sodium carbonate to hard water soften it? (use an equation)
Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble.
The carbonate ions from sodium carbonate react with the calcium and magnesium ions in the water to produce insoluble precipitates. For example:
calcium ions + sodium carbonate → calcium carbonate + sodium ions
Ca2+(aq) + Na2CO3(aq) → CaCO3(s) + 2Na+(aq)
The water is softened because it no longer contains dissolved calcium ions and magnesium ions. It will form lather more easily with soap.
What are the advantages of hard water?
can improve the taste of the water
are good for the development and maintenance of bones and teeth can help to reduce heart disease
How do ion exchange columns work?
The resin beads have sodium ions attached to them. As the hard water passes through the column, the calcium and magnesium ions swap places with the sodium ions.
The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions. The hard water is softened because it no longer contains calcium or magnesium ions. Some ion exchange resins use hydrogen ions instead of sodium ions.
What is an aquifer?
An aquifer is an underground layer of permeable rock, gravel or sand that is soaked with water
How can you test if water is pure?
measuring its boiling point
evaporating it (to dryness) on an evaporating dish
Why is silver used in filter cartridges?
Silver nanoparticles have an antibacterial effect. Their presence in the filter prevents the growth of bacteria within the filter if water is left inside it for long periods. Silver nanoparticles also help break down harmful pesticides which might be in the water.
What does soft water form with soap?
Lather.
What determines whether water is soft or hard?
The types of rocks found in different regions determines how hard or soft the water will be. The water in some parts of the country is soft because it has low levels of dissolved calcium and magnesium compounds, while the water in other parts of the country is hard because it has higher levels of dissolved calcium and magnesium compounds.
What is the difference between temporary hard water, and permanent hard water?
Temporary hard water can be softened by boiling it. Permanent hard water stays hard, even when it is boiled.
Why is rainwater naturally slightly acidic?
because it contains carbonic acid, formed by the reaction between water and carbon dioxide in the atmosphere.
What is Hard Water?
Is water that contains dissolved compounds, usually calcium or magnesium compounds.
What are the disadvantages of hard water?
More soap is needed to produce lather, which increases costs. This happens with temporary or permanent hardness.
The scum produced is unsightly - spoiling the appearance of baths and shower screens, for example.
Temporary hardness can reduce the efficiency of kettles and heating systems
What are boreholes?
In countries where water is scarce, boreholes are drilled to reach water underground.
What happens to the water after the sedimentation tank and why?
Chlorine is added to drinking water to sterilise it. The chlorine kills microbes - including microbes that cause potentially-fatal diseases such as typhoid, cholera and dysentery.
What is the chemical formula of sodium carbonate and what is it also known as?
Sodium carbonate, Na2CO3, is also known as washing soda.
Why does temporary hard water reduce the efficiency of heating systems?
This is because limescale (a solid containing calcium carbonate) is produced when the water is heated. It coats the heating element in kettles, and the inside of boilers and hot water pipes. This means more energy is needed to heat the water, again increasing costs. Pipes may become blocked by limescale - causing the heating system to break down.
What happens when you evaporate pure water?
Pure water will leave no solids behind when it is evaporated, whereas impure water will leave solids behind on the evaporating dish.
How do ion exchange columns work?
The resin beads have sodium ions attached to them. As the hard water passes through the column, the calcium and magnesium ions swap places with the sodium ions.
The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions. The hard water is softened because it no longer contains calcium or magnesium ions. Some ion exchange resins use hydrogen ions instead of sodium ions.
What are boreholes?
In countries where water is scarce, boreholes are drilled to reach water underground.
What are the sources of water typically used in the UK?
lakes, rivers, aquifers and reservoirs.
Why is water from the tap not pure?
because it contains dissolved mineral ions and chlorine.
What are the advantages of using ion exchange columns?
Sodium chloride is cheap and widely available, making this a convenient and cost-effective system.
What do water filter cartridges contain?
silver to kill bacteria
carbon (‘activated charcoal’) to absorb impurities, eg chlorine
ion exchange resins to soften the water, and remove heavy metal ions (such as lead ions)
How can you soften hard water?
Methods for softening hard water involve the removal of calcium ions and magnesium ions from the water.
There are two methods for softening hard water:
adding sodium carbonate to the water
using ion exchange columns
What happens to pure water and its boiling point?
Pure water boils at 100°C, but its boiling point increases as the concentration of dissolved salts increases.
What are the advantages of filtering water at home?
Filtering removes impurities and this can improve the taste and quality of the water. Filtering also helps to soften the water.
How do you first filter the water?
Solids in the water, such as leaves and soil, must be removed with the screen. The water is sprayed onto specially-prepared layers of sand and gravel called filter beds.
Different-sized insoluble solids are removed as the water trickles through the filter beds. These are cleaned every so often by pumping clean water backwards through the filter.
What is the order by which water is purified?
Screen, coarse filter, sedimentation tank, Fine filter, chrlorine added, then into a storage tanks, and then into homes and factories.
Why is silver used in filter cartridges?
Silver nanoparticles have an antibacterial effect. Their presence in the filter prevents the growth of bacteria within the filter if water is left inside it for long periods. Silver nanoparticles also help break down harmful pesticides which might be in the water.
How can you test if water is pure?
measuring its boiling point
evaporating it (to dryness) on an evaporating dish
What happens when you evaporate pure water?
Pure water will leave no solids behind when it is evaporated, whereas impure water will leave solids behind on the evaporating dish.
Why does temporary hard water get softened when boiled?
Temporary hard water contains dissolved hydrogen carbonate ions, HCO 3–. When heated, these ions decompose (break down) to form carbonate ions, CO3 2–. The carbonate ions in the boiled water react with dissolved calcium and magnesium ions to form insoluble precipitates (calcium carbonate and magnesium carbonate).
What is a resourvoir?
a reservoir is usually an artificial lake, made by building a dam to accumulate and save river water in the valley behind.
What must we do to produce water of suffucient quality?
choose an appropriate source of water
filter the water
chlorinate the water
Why is water from the tap not pure?
because it contains dissolved mineral ions and chlorine.
What are the disadvantages of using sodium carbonate to soften hard water?
the calcium carbonate and magnesium carbonate precipitates to form limescale. As well as being unsightly on your taps, it can also clog up pipes in heating systems (causing them to break down). This makes treatment with sodium carbonate suitable for softening water only in certain circumstances - such as softening water for hand washing clothes.
What are the arguements agaisnt fluorine being added to water?
has been linked to tooth mottling (staining), bone disease and pain
forces people to consume fluoride when they drink tap water - taking away their personal choice (making it unethical)
How do you perform a titration with a soap solution to find out that hardness of water?
A known volume of water is put into a conical flask. Soap solution is added to it from a burette or pipette. The mixture is swirled to help it form lather. The volume of soap solution that needs to be added to form permanent lather is recorded. The harder the water, the greater the volume of soap solution needed.
How do you first filter the water?
Solids in the water, such as leaves and soil, must be removed with the screen. The water is sprayed onto specially-prepared layers of sand and gravel called filter beds.
Different-sized insoluble solids are removed as the water trickles through the filter beds. These are cleaned every so often by pumping clean water backwards through the filter.
What must we do to produce water of suffucient quality?
choose an appropriate source of water
filter the water
chlorinate the water
How does the carbonic acid in rainwater react with hard water?
Carbonic acid in rainwater reacts with this to produce soluble calcium hydrogencarbonate:
carbonic acid + calcium carbonate → calcium hydrogencarbonate
H2CO3(aq) + CaCO3(s) → Ca(HCO3)2(aq)
What must have to resin beads after softening hard water?
Once the resin beads in dishwashers become saturated with calcium and magnesium ions, they must be regenerated by adding sodium chloride (common salt). The sodium ions it contains replace the calcium and magnesium ions on the beads.
Why does permanent hard water not get softened when boiled?
Permanent hard water contains dissolved sulfate ions, SO4 2–. These do not decompose when heated. They remain dissolved and do not react with calcium and magnesium ions - so the water stays hard even when boiled.
What happens to pure water and its boiling point?
Pure water boils at 100°C, but its boiling point increases as the concentration of dissolved salts increases.
What are the sources of water typically used in the UK?
lakes, rivers, aquifers and reservoirs.
What are the advantages of filtering water at home?
Filtering removes impurities and this can improve the taste and quality of the water. Filtering also helps to soften the water.
What are ion exchange columns?
Commercial water softeners often use ion exchange resins. These substances are usually made into beads, which are packed into cylinders called ion exchange columns. These can be built into machines, such as dishwashers, or plumbed into water systems to continuously soften the water.
Why did Dmitri Mendeleev leave gaps in his table?
Sometimes this method of arranging elements meant there were gaps in his horizontal rows or ‘periods’. But instead of seeing this as a problem, Mendeleev thought it simply meant that the elements which belonged in the gaps had not yet been discovered.
Who proposed the idea of using atomic number to order the elements and why?
Using atomic number instead of atomic mass as the organising principle was first proposed by the British chemist Henry Moseley in 1913. It explained why Mendeleev needed to change the order of some of the elements in his table.
What factors gave more success to Mendeleev’s table?
Despite leaving gaps, he was able to work out the atomic mass of the missing elements, and so predict their properties. And when they were discovered, Mendeleev turned out to be right.
What was discovered that allowed Mendeleev’s table to be refined?
the discovery of protons, neutrons and electrons in the early 20th century allowed Mendeleev’s table to be refined into the modern periodic table.It involved an important modification – the use of atomic number to order the elements.
How did people react to Mendeleev’s table?
Was seen as a curiosity to begin with, but then as a useful tool when the predicted elements were discovered later
What are the group 1 elements called?
The alkali metals.
What are the properties of transition metals?
They are high density they have a high melting point they have low reactivity (not very reactive with water, air or acid) They are strong and hard They make coloured compounds
Why do elements in the same group have similar properties?
The elements in a group all have the same number of electrons in their highest occupied energy level (also referred to as the outer shell). This is why they have similar chemical properties.
Who else created a periodic table based on ordering the elements by relative atomic mass?
In 1869, just five years after John Newlands put forward his Law of Octaves, a Russian chemist called Dmitri Mendeleev published a periodic table. Mendeleev also arranged the elements known at the time in order of relative atomic mass. But he also realised that the physical and chemical properties of elements were related to their atomic mass in a ‘periodic’ way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table.
What was the problem about ordering the elements with atomic mass?
It could be difficult for Mendeleev to group elements in similar properties, for example: iodine has a lower relative atomic mass than tellurium, so it should come before tellurium in Mendeleev’s table.In order to get iodine in the same group as other elements with similar properties - such as fluorine, chlorine and bromine - he had to put it after tellurium, which broke his own rules
Why do elements in group 7 get less reactive as you go down the group?
elements in Group 7 gain one electron into their highest occupied energy level (outer shell) to form ions with a –1 charge.
As you go down the group, the number of occupied energy levels (filled shells) increases. The higher the energy level of the outer electrons, the greater the distance from the nucleus, and the less easily electrons are gained.
Why was John Newlands’ table not accepted by other scientists?
Newlands’ table showed a repeating or periodic pattern of properties, but this pattern eventually broke down. By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties
What does the reactivity of an element depend on?
The reactivity of an element depends on how easily its atoms lose or gain electrons.
What do many transition metals act as?
A catalyst.
What happens as you go down the elements in group 7?
The melting and boiling points increase, and the colours of the elements become darker and the halogens become less reactive.
What were the similarities of Newlands and Mendeleev’s tables?
Both Ordered elements by atomic weight.
What are the ionic compounds that group 1 metals produce?
The ionic compounds produced are white solids which form colourless solutions when they dissolve.
What was the law of octaves and who put it forward?
An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass.
When he did this, he found a pattern among the early elements. The pattern showed that each element was similar to the element eight places ahead of it. He then put the similar elements into vertical columns, known as groups.
What were the differences of Newlands’ and Mendeleev’s tables?
Newlands table only included the elements known at the time, whilst Mendeleev left gaps for elements he predicted would be discovered later. Newland maintained a strict order of atomic weights whilst Mendeleev Swapped the order of some elements if that fitted their properties better.In Newlands’ table every eighth element had similar properties, but in Mendeleev’s table elements in groups had similar properties.
What is the equation for the reaction between an alkali metal and water?
group 1 metal + water → group 1 metal hydroxide + hydrogen
2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)
(M stands for the symbol of a Group 1 metal)
What are the common properties of Halogens?
they are non-metals
they have low melting and low boiling points
they are brittle when solid
they are poor conductors of heat and electricity
they have coloured vapours
their molecules are diatomic (each contain two atoms)
they are toxic
What are the elements between groups 2 and 3 called?
The transition metals.
What are the common colours of group 7 elements?
Fluorine is very pale yellow, chlorine is yellow-green and bromine is red-brown. Iodine crystals are shiny purple-black but easily turn into a dark purple vapour when they are warmed up.
How did people react to Newlands’ table?
Was criticised by other scientists for grouping some elements with others when they were obviously very different to each other
What happens during displacement reactions in the halogens?
In these reactions, a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
What happens as you go down the group 1 metals?
They get more reactive.
Why do elements in group 1 get more reactive as you go down the group?
elements in Group 1 lose the electron from their highest occupied energy level (outer shell) to form ions with a +1 charge.
As you go down the group, the number of occupied energy levels (filled shells) increases. The higher the energy level of the outer electrons, the greater the distance from the nucleus, and the more easily electrons are lost
What are the group 7 elements called?
halogens
How do you make ammonia?
You react hydrogen with nitrogen over an iron catalyst to form ammonia, in a reversible reaction.
What are the properties of alkali metals?
they are very soft and can be cut easily with a knife
they have low densities (lithium, sodium and potassium will float on water)
they react quickly with water - producing hydroxides and hydrogen gas
their hydroxides dissolve in water to form alkaline solutions
low melting points and boiling points compared to other metals.
