Chemistry 2: Chemical Resources

Question	Answer
GCSE Chemistry B OCR Gateway	Chemistry 2: Chemical Resources
Which three sections of the Earth make up its structure?	The Earth is made of a layered structure. It has three sections, a: - thin, rocky crust - mantle - core (containing iron).
Why is it difficult to collect information about the structure of the Earth?	It is difficult to collect information about the structure of the Earth as the deepest mine and holes drilled into the crust are only a few kilometres deep into the thick crust. Diagram 1
What do scientists have to rely on studying in order to understand the structure of the Earth?	Scientists have to rely on studying seismic waves (vibrations) caused by earthquakes to understand the structure of the Earth.
What is the Earth's lithosphere?	The Earth's lithosphere is the relatively cold, rigid outer part of the Earth, made of the crust and top part of the mantle.
What is the top of the lithosphere 'cracked' into?	The top of the lithosphere is 'cracked' into several large interlocking pieces called tectonic plates.
What are the two types of tectonic plates?	The two types of tectonic plates are: - Oceanic plates - Continental plates.
Where do the oceanic plates sit?	The oceanic plates sit under the ocean, forming its pieces.
What do the continental plates form?	The continental plates form the continents.
List the five tectonic plates that make up the Earth. Chemistry 2: Chemical Resources, page 26	The five tectonic plates that make up the Earth are the: - North American plate - Eurasian plate - African plate - South American plate - Nazca plate. Diagram 2
Why do the plates sit on top of the mantle?	The plates sit on top of the mantle because they are less dense than the mantle.
Do plates move slowly or quickly?	Plates move very slowly (approximately 2.5cm per year).
What do these movements cause at the boundaries between plates? Chemistry 2: Chemical Resources, page 26	These movements cause earthquakes and volcanoes at the boundaries between plates. Diagram 3
Just below the crust, what form does the mantle take?	Just below the crust, the mantle takes the form of being relatively cold and rigid.
What happens to the mantle at greater depths?	At greater depths, the mantle becomes hot and fluid, which means that it can flow.
What is formed by heat released from radioactive decay in the core?	Convection currents are formed by heat released from radioactive decay in the core.
What do convection currents cause, in reference to magma (molten rock)?	Convection cause magma (molten rock) to rise to the surface at the boundaries of plates.
How is new igneous rock formed?	New igneous rock is formed, when the molten rock solidifies.
What causes the plates to move?	This slow movement of the magma causes the plates to move.
Which has the higher density, oceanic crust or continental crust?	Oceanic crust has a higher density than continental crust.
What is subduction?	When an oceanic plate collides with a continental plate, it dips down and slides under it. This is subduction. The oceanic plate is partially re-melted as it goes under the continental plate.
What does the diagram, Chemistry 2: Chemical Resources, page 27, show?	The diagram shows what is the cause of the plate's movement. Diagram 4
Have there been many theories put forward to explain changes in the Earth's surface?	Yes
Which theory do scientists now accept?	Scientists now accept the theory of plate tectonics.
Why is the theory of plate tectonics widely accepted?	The theory of plate tectonics is widely accepted as it explains a range of evidence and has been discussed and tested by many a scientist.
What did Alfred Wegener suggest in 1914 about the surface of the Earth?	Alfred Wegener, in 1914, suggested that the surface of the Earth was changing.
Which idea did Wegener develop?	Wegener developed the idea that, millions of years ago, all the continents were joined together.
Which other features on the Earth's surface did Wegener notice?	Wegener noticed several other features on the surface of the Earth: - The continents look like the would fit together like a jigsaw. - The geology of Scotland and Canada was similar, as was the geology of Africa and South America. - Similar animal species were found on either side of the Atlantic, e.g. caribou in Canada and reindeer in Scandinavia.
Where Wegener's ideas initially accepted?	No
What supported Wegener's theory in the 1960s?	In the 1960s Wegener's theory was supported by studies which looked at new rock formed at oceanic plate boundaries.
What did the studies of the 1960s show?	The studies of the 1960s showed that: - the plates are moving apart - the age of rock increases as you move away from the boundary.
Where do volcanoes form?	Volcanoes form where magma (molten rock underneath the Earth's surface) can find its way through weaknesses in the Earth's crust.
In which places are there weaknesses in the Earth's crust?	The weaknesses in the Earth's crust are often at plate boundaries or where the crust is very thin.
Why does the magma rise through the crust?	The magma rises through the crust because it has a lower density than the crust.
Why do geologists study volcanoes?	Geologists study volcanoes to help understand the structure of the Earth.
Why do geologists aim to predict when eruptions will occur?	Geologists also aim to predict when eruptions will occur, to give an early warning to people living nearby.
Why can living near a volcano be dangerous?	Living near a volcano can be dangerous because eruptions can't be predicted with accuracy.
Why do some people choose to live by a volcano?	Some people choose to live by a volcano because volcanic soil is very fertile.
Even though geologists are better at being able to predict when eruptions will occur, what are the predictions never to be?	Even though geologists are better at being able to predict when eruptions will occur, predictions are never 100% accurate.
What is lava	Lava is molten rock above the surface.
What is magma?	Magma is molten rock below the surface.
When lava cools what is formed?	When lava cools igneous rock is formed.
Do all volcanoes have lava with the same degree of thickness?	No, some volcanoes have runny lava and others have thicker lava.
Which lava erupts more violently and catastrophically?	Thick lava erupts more violently and catastrophically.
What happens when liquid rock cools?	When liquid rock cools, igneous rock is formed.
What are igneous rocks?	Igneous rocks are very hard and have interlocking crystals of different sizes: - Large crystals are made when the rock cools slowly, as in silica-rich granite and iron-rich gabbro. - Small crystals are made when the rock cools quickly, as in silica-rich rhyolite and iron-rich basalt.
What does rhyolite lava make?	Rhyolite lava makes pumice, volcanic ash and bombs.
Which construction materials come from rocks found in the Earth's crust?	Many construction materials come from rocks found in the Earth's crust: - Iron and aluminium are extracted from rocks called ores. - Brick is made by baking clay that has been extracted from the Earth. - Glass, concrete and cement are all made from sand (small grains of rock). - Limestone, marble, granite and aggregates (gravel) are types of rock extracted from the Earth. These rocks just need to be shaped to be used as building materials.
Which material is the easiest to shape?	Limestone is the easiest to shape because it's the softest.
Which material is the hardest to shape?	Granite is the hardest to shape because it's the hardest.
Why do rocks differ in hardness?	Rocks differ in hardness because of the ways in which they were made: - Limestone is a sedimentary rock. - Marble is a metamorphic rock. - Granite is a igneous rock.
What is marble made from?	Marble is made from limestone that has been put under pressure and heated, making it harder.
What are limestone and marble mainly made of?	Limestone and marble are mainly made of calcium carbonate (CaCO3).
What happens to calcium carbonate when it is heated?	When calcium carbonate is heated it breaks down into calcium oxide and carbon dioxide.
Give the word equation for calcium carbonate.	calcium carbonate → calcium oxide + carbon dioxide
Give the symbol equation for calcium carbonate.	CaCO3 (s) → Ca(s) + CO2(g)
What type of reaction is that of calcium carbonate?	This type of reaction is called a thermal decomposition reaction; one material breaks down into two or more new substances when heated.
What does a combination of heated clay and limestone make?	Clay and limestone can be heated together to make cement.
What is used to make concrete?	Cement can be mixed with sand, aggregates and water and allowed to set to make concrete.
Is concrete hard and strong?	Concrete is very hard but not very strong.
How can concrete be strengthened?	Concrete can be strengthened by allowing it to set around steel rods to reinforce it.
What sort of material is reinforced concrete?	Reinforced concrete is a composite material
What is a composite material?	A composite material is when the best properties of each component material are combined.
What does reinforced concrete combine?	Reinforced concrete combines the strength and flexibility of the steel bars with the hardness of the concrete.
Does reinforced concrete have many more or many less uses than ordinary concrete?	Reinforced concrete has many more uses than ordinary concrete.
Whereabouts is rock dug out of?	Rock is dug out of the ground in mines and quarries.
What do mining and quarrying companies have to do on the local area and environment?	Mining and quarrying companies have to do reduce their impact on the local area and environment.
Why must mining and quarrying companies reduce their impact of the local area and environment?	Mining and quarrying companies must reduce their impact of the local area and environment because mines and quarries can: - be noisy and dusty - take up land - change the shape of the landscape - increase the local road traffic.
What will a responsible company to after it has finished working on an area?	A responsible company will also reconstruct, cover up and restore any area that it has worked on.
Where is copper extracted from?	Copper is extracted from naturally occurring copper ore.
How is copper extracted?	Copper is extracted by heating it with carbon.
Give the word equation to make copper.	copper oxide + carbon → copper + carbon dioxide
Give the symbol equation to make copper.	2CuO(s) + C(s) → 2Cu(s) + CO2(g)
What does the process of extracting copper use?	The process of extracting copper uses a lot of energy.
How does this affect the expense of extracting copper?	The expense of extracting copper is greatly increased.
What is removed from the copper oxide?	Oxygen is removed from the copper oxide.
What is the process of removing oxygen from copper oxide called?	The process of removing oxygen from copper oxide is called reduction.
Is it cheaper to recycle copper than to extract it from its ore?	Yes
What does recycling copper also do?	Recycling copper also conserves the world's limited supply of copper ore and uses less energy.
Why is recycling copper more difficult?	Recycling copper is more difficult as it has other metals stuck to it or mixed with it.
If copper is very impure what can it be purified using, before it can be used again?	If copper is very impure, it can be purified using electrolysis (an expensive process) before it can be used again.
What does electrolysis use in order to break down compounds into simpler substances?	Electrolysis uses an electric current to break down compounds into simpler substances.
In electrolysis, what is electricity passed through?	In electrolysis, electricity is passed though a liquid or a solution called an electrolyte, e.g. copper(ll) sulfate solution - containing copper ions, to make simpler substances.
What are used to allow the electricity to flow through the electrolyte?	Electrodes are used to allow the electricity to flow through the electrolyte.
What is the anode made of?	The anode is made of impure copper: Cu - 2e- → Cu2+ This is an oxidation process as electrons are lost.
What charge does the anode have?	The anode has a positive charge, equalling a positive electrode.
Does the anode lose mass or gain mass? Chemistry 3: Chemical Resources, page 30	The anode (impure copper electrode) loses mass as the copper oxidises. Diagram 6
What is the cathode made of?	The cathode is made of pure copper: Cu2+ 2e- → Cu This is a reduction process as electrons are gained.
Which charge does a cathode have?	The cathode has a negative charge, equalling a negative electrode.
Does the cathode gain mass or lose mass? Chemistry 3: Chemical Resources, page 30	The cathode (pure copper electrode) gains mass as copper is deposited. Diagram 6
What is an alloy?	An alloy is a mixture of a metal with another element (usually another metal).
Give examples of two alloys.	Bronze and steel are alloys.
What do alloys do to a metal?	Alloys improve the properties of a metal and make them more useful - they are often harder and stronger than pure metal.
Give three examples of alloys used in everyday life.	Examples of alloys used in everyday life: - amalgam (made using mercury) is used for fillings in teeth - solder (made of lead and tin) is used to join wires - brass (made of copper and zinc) is used in door handles, coins and musical instruments.
What is a smart alloy?	A smart alloy such an nitinol (an alloy of nickel and titanium) can be bent and twisted. Nitinol will return to its original shape when it is heated; it has shaped memory.
What can nitinol be used for?	Nitinol can be used for the frames of reading glasses.
Which materials are used to make cars?	Many different materials are used to make cars: - Nylon fibre is used to make the seatbelts because it's strong and flexible. - Glass is used to make the windscreen because it's transparent. - Copper is used for the wiring in the engine because it's a good electrical conductor. - Plastic is used for the trip because it's rigid and doesn't corrode. - Steel is used to make the body because it's strong and malleable. - Aluminium is used to make the alloy wheels because it's lightweight and doesn't corrode in moist conditions.
In the table, Chemistry 2: Chemical Resources, page 31, compare the properties of aluminium and iron.	Property - P Aluminium - A Iron - I P: Dense A: No I: Yes P: Magnetic A: No I: Yes P: Resists corrosion A: Yes I: No P: Malleable A: Yes I: Yes P: Conducts electricity A: Yes I: No Table 1
Which other metals can aluminium be mixed with to make an alloy?	Aluminium can be mixed with other metals, such as copper and magnesium, to make an alloy.
Do alloys have different or similar properties from the metals that they are made from?	Alloys have different properties from the metals that they are made from.
What do these properties make the alloy?	These properties make the alloy more useful.
What is steel an alloy of?	Steel is an alloy of iron and carbon.
Why is steel used to make cars?	Steel is used to make cars because it: - is harder and stronger than iron - doesn't corrode as fast as iron.
Which metal is also used to make car bodies?	Aluminium
In comparison to steel which properties does aluminium have?	In comparison to steel, aluminium: - is lighter - corrodes less - is more expensive.
Why will aluminium have a longer lifetime if it is used to make a car?	If aluminium is used to make a car, it will have a longer lifetime because aluminium doesn't corrode.
Why will the car have a better fuel economy if made with aluminium?	As aluminium is less dense than steel, the car will be lighter and so have a better fuel economy.
What is rusting an example of?	Rusting is an example of an oxidation reaction, i.e. a reaction where oxygen is added to a substance.
Which does rusting need?	Rusting needs: - iron - water - oxygen (air).
When does rusting happen even faster?	Rusting happens even faster when the water is salty or acid rain.
Why doesn't aluminium react and corrode in air and water?	Aluminium doesn't react and corrode in air and water. Instead, it quickly forms a protective layer of aluminium oxide.
What does this layer of aluminium oxide do?	This layer of aluminium oxide stops any more air or water from coming into contact with the metal. This built-in protection will not flake off.
Can most materials in a car be recycled?	Yes
Since 2006, what does the law state about the recycling of a car?	Since 2006, the law states that 85% of a car must be able to be recycled.
When does this increase to 95%?	The law increases to 95% in 2015.
What can separating all the different materials for recycling result in?	Separating all the different materials for recycling can result in a tricky and time-consuming process. But it saves natural resources and avoids disposal problems.
What does recycling materials mean?	Recycling materials means: - less quarrying is required - less energy is used to extract them from ores - the limited ore reserves will last longer (saves natural resources) - disposal problems are reduced.
What does recycling the plastics and fibres help with?	Recycling the plastics and fibres reduces the amount of crude oil needed to make them, and conserves oil reserves.
Which materials of a car would cause pollution if put into a landfill?	There are a number of materials in a car that would cause pollution if put into landfill, e.g. lead in the car battery.
What does this mean about recycling if pollution from landfill sites is prevented?	This means that recycling also prevents the environment.
What is ammonia (NH3)?	Ammonia (NH3) is an alkaline gas made from nitrogen and hydrogen.
What can ammonia be used to make?	Ammonia can be used to make: - nitric acid - fertilisers.
How are cheap fertilisers important?	Cheap fertilisers are important in helping to produce enough food for the growing world population.
Is the reaction which makes ammonia reversible?	Yes
What does this mean, in reference to the reaction being reversible?	This means that nitrogen and hydrogen can form ammonia, and ammonia can decompose to make hydrogen and nitrogen.
What is a reversible reaction?	A reversible reaction is a reaction that can go forwards or backwards under the same conditions.
In which process is ammonia made on a large scale?	Ammonia is made on a large scale in the Haber process.
What are the two reactants in the Haber process that make ammonia?	The two reactants are: - nitrogen (from the air) - hydrogen (from natural gas or the cracking of crude oil).
Why aren't optimum conditions used in the making of ammonia?	Optimum conditions aren't used as they would be very expensive to maintain.
Describe the compromise reached for the conditions used in the Haber process.	The compromise reached for the conditions used in the Haber process: - The nitrogen and hydrogen mixture is under a high pressure of 200 atmospheres. - The gases are passed over an iron catalyst at 450°C.
What percentage of the reactant gases make ammonia?	15% of the reactant gases make ammonia.
What happens to the unreactant gases?	The unreactant gases are recycled.
Once it has been made, what happens to the ammonia?	Once made, the ammonia is cooled, condensed and then pumped off as a liquid.
In the diagram, Chemistry 3: Chemical Resources, page 33 what is being shown?	In the diagram, the Haber process of the making of ammonia is being shown. Diagram 7
What does the cost of making a new substance depend on?	The cost of making a new substance depends on: - the price of energy (gas and electricity) - labour costs (wages for employees) - how quickly the new substance can be made (cost of catalyst) - the cost of starting materials (reactants) - the cost of equipment (plant and machinery).
Which factors affect the cost of making a new substance?	The factors that affect the cost of making a new substance include: - the pressure - the higher the pressure, the higher the plant cost - the temperature - the higher the temperature, the higher the energy cost - the catalysts - catalysts can be expensive to buy, but production costs are reduced because they increase the rate of reaction - the number of people needed to operate machinery - automation reduces the wages bill - the amount of unreacted material that can be recycled - recycling reduces costs.
What are indicators?	Indicators are chemicals that change colour to show changes in pH.
What is the difference between indicators?	Some indicators, e.g. litmus, have only two colours; others, e.g. universal indicator, have a range of colours over different pH values.
What are acids?	Acids are substances with a pH of less than 7.
What are bases?	Bases are the oxides and hydroxides of metals, with a pH of greater than 7.
Which colour does acid turn litmus indicator?	Acid turns litmus indicator red.
Which colour do bases turn litmus indicator?	Bases turn litmus indicator blue.
What are soluble bases?	Soluble bases are chemicals with a pH greater than 7 and that dissolve in water. They are called alkalis.
How can you find the pH of a solution? Chemistry 2: Chemical Resources, page 35	You can find the pH of a solution by using universal indicator. You can add a few drops of universal indicator to the solution and compare the resulting colour against a pH colour chart. Diagram 8
What are metal oxides and metal hydroxides?	Metal oxides and metal hydroxides are bases.
What happens when bases are added to acids in the correct amounts?	When bases are added to acids in the correct amounts, they can cancel each other out. This is called neutralisation because the resulting solution has a neutral pH of 7.
Give the word equation for a neutralisation reaction between an acid and base.	acid + base → salt + water
What happens when an acid is added to an alkali?	When an acid is added to an alkali, the pH of the solution decreases because the acid neutralises the alkali to reach pH 7.
What happens when an alkali is added to an acid?	When an alkali is added to an acid, the pH of the solution increases because the alkali neutralises the acid to reach pH 7.
What can acids also be neutralised by?	Acids can also be neutralised by carbonates.
What does this neutralisation produce?	This neutralisation produces a salt, water and carbon dioxide gas.
Give the word equation for the neutralisation between an acid and carbonate.	acid + carbonate → salt + water + carbon dioxide
Where does the first name of a salt come from?	The first name of a salt comes from the name of the base or carbonate used.
Give examples where the first name of a salt comes from the name of the base or carbonate used.	For example: - sodium hydroxide will make a sodium salt - copper oxide will make a copper salt - calcium carbonate will make a calcium salt - ammonia will make an ammonium salt.
Where does the second name of a salt come from?	The second name of a salt comes from the acid used.
Give examples where the second name of the salt comes from the acid used.	For example: - hydrochloric acid will produce a chloride salt - sulfuric acid will produce a sulfate salt - nitric acid will produce a nitrate salt - phosphoric acid will produce a phosphate salt.
Give an example on a salt named from a base or carbonate used and an acid used.	For example, neutralising potassium hydroxide with nitric acid will produce potassium nitrate.
What do alkalis in solution contain?	Alkalis in solution contain hydroxide ions, OH-(aq).
What do acids in solution contain?	Acids in solution contain hydrogen ions, H+(aq).
What is the pH of a solution a measure of?	The pH of a solution is a measure of the concentration of H+ ions.
Which ionic equation can neutralisation be described through?	H+(aq) + OH-(aq) → H2O(l)
What does the table, Chemistry 2: Chemical Resources, page 36, infer?	The table infers that you should be able to construct any of the following word equations and balanced symbol equations for produce salts. Table 2
What are fertilisers?	Fertilisers are chemical that give plants essential chemical elements needed for growth. Fertilisers: - make crops grow faster and bigger - increase the crop yield.
What can fertilisers do as world populations rise?	Fertilisers can increase food supply, as world populations rise.
Which problems can fertilisers cause?	Fertilisers can cause problems such as the death of animals in waterways. This is known as eutrophication.
Why must fertilisers be soluble in water?	Fertilisers must be soluble in water so that they can be taken in by the roots of plants in solution.
How do fertilisers increase crop yield?	Fertilisers increase crop yield by: - replacing essential elements in the soil that have been used up by a previous crop - providing nitrogen as soluble nitrates which are used by the plant to make protein for growth.
How can some fertilisers be manufactured?	Some fertilisers can be manufactured by neutralising an acid with an alkali: - Ammonium sulfate - neutralise sulfuric acid with ammonia. - Ammonium nitrate - neutralise nitric acid with ammonia. - Ammonium phosphate - neutralise phosphoric acid with ammonia. - Potassium nitrate - neutralise nitric acid with potassium hydroxide.
How can a fertiliser be made?	A fertiliser, e.g. potassium nitrate, can be made by producing a salt from neutralisation.
List the stages in which a fertiliser can be made from neutralisation. Chemistry 2: Chemical Resources, page 37	1) Measure out the alkali (e.g. potassium hydroxide) into a beaker using a measuring cylinder. 2) Add acid (e.g. nitric acid) from a burette. Use a glass rod to put a drop of solution onto indicator paper (to test pH). A the acid a bit at a time until the solution is neutral (pH 7). 3) Transfer the solution to an evaporation dish. Evaporate the solution until crystals form on the end of a cold glass rod. Leave to cool and crystallise. Diagram 9
List the equipment need to make a fertiliser by neutralisation.	Measuring cylinder, beaker, burette, glass rod, indicator paper, filter funnel, evaporating dish, boiling water, gauze, tripod, Bunsen burner.
What is eutrophication?	Eutrophication is when the overuse of fertilisers changes the ecosystem in lakes, rivers and streams.
Describe the three stages in which eutrophication takes place. Chemistry 2: Chemical Resources, page 37	1) Fertilisers used by farmers may be washed into lakes and rivers (run-off). This increases the levels of nitrates and phosphates in the water and more simple algae grow. 2) The algal bloom blocks off sunlight to other plants, causing them to die and rot. 3) Aerobic bacteria feed on the dead organisms and increase in number. They quickly use up the oxygen until nearly all the oxygen is removed. There isn't enough oxygen left to support the larger organisms, such as fish and other aquatic animals, so they suffocate. Diagram 10
What do you need to be able to interpret in reversible reactions?	You need to be able to interpret data percentage yield, data on other industrial processes in terms of rate and percentage yield and cost in reversible reactions.
What do economic considerations determine in the manufacture of chemicals?	Economic considerations determine the conditions used in the manufacture of chemicals: - The percentage yield achieved must be high enough to produce enough daily yield of product (a low percentage yield is acceptable providing the reaction can be repeated many times with recycled starting materials). - The rate of reaction must be high enough to produce enough daily yield of product. - The optimum conditions should be used to give the most economical reaction (this could mean a slower reaction or a lower percentage yield at a lower cost).
Which three things are important in the manufacture of ammonia, in reference to the amount, time and cost?	It is important that the maximum amount of ammonia is made in the shortest possible time at a reasonable cost.
What are the three benefits and problems with a low temperature, high pressure and catalyst, in the Haber process?	For the Haber process: - a low temperature increases yield but the reaction is too slow - a high pressure increases yield but becomes more expensive as yield increases - a catalyst increases the rate of reaction but doesn't change the percentage yield.
What is the compromise reached?	A compromise is reached of: - temperature of 450°C - pressure of 200 atmospheres - catalyst of iron.
What does this give in terms of reaction and percentage yield?	This gives a fast reaction with an acceptable percentage yield.
What is sodium chloride used as?	Sodium chloride, or table salt, is used as a food preservative and flavouring. But it is also useful as a raw material in the chemical industry.
What id sodium chloride an important source of?	Sodium chloride is an important source of chlorine and sodium hydroxide.
Where can sodium chloride be obtained from?	Sodium chloride is removed from the sea or mined from salt deposits.
Where can sodium chloride be mined?	Sodium chloride is mined: - in Cheshire as a solid (rock salt). - by solution mining for the chemical industry.
What has the mining of sodium chloride led to in some parts of Cheshire?	The mining of sodium chloride has led to subsidence in some parts of Cheshire.
When concentrated sodium chloride solution is electrolysed, why must the electrodes be made from inert materials?	When concentrated sodium chloride solution is electrolysed, the electrodes must be made from inert materials as the products are very reactive.
What does this process (of the electrolysis of sodium chloride) form? Chemistry 2: Chemical Resources, page 39	This process forms: - sodium hydroxide in the solution. - hydrogen at the cathode - chlorine at the anode. Diagram 11
How can you test for chlorine?	You can test for chlorine using damp litmus paper; if chlorine is present, it will bleach the litmus paper.
What are the uses for the products of electrolysis of sodium chloride?	There are many uses for the products of electrolysis of sodium chloride: - Sodium hydroxide is used to make soap. - Hydrogen is used in the manufacture of margarine. - Chlorine is used to sterilise water, make solvents and plastics, for example, PVC. - Chlorine and sodium hydroxide are reacted together to make household bleach.
What does brine (NaCl(aq)) contain?	Brine (NaCl(aq)) contains Na+, Cl-, OH- and H+ ions.
What does the large scale electrolysis of brine happen as?	The large scale electrolysis of brine happens as part of the chloro-alkali industry.
What does this global market generate?	This global market generates great profits.
How is hydrogen made?	Hydrogen is made by reduction at the cathode: 2H+ +2e- → H2
What is reduction?	Reduction is gain of electrons.
How is chlorine made?	Chlorine is made by oxidation at the anode: 2Cl- - 2e- → Cl2
What is oxidation?	Oxidation is loss of electrons.
Which two ions remain in the solution?	Sodium (Na+) and hydroxide (OH-) ions remain in the solution.
What do the remaining ions of sodium and hydroxide make?	The remaining ions make the third product of sodium hydroxide.

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