Chapter 11

Question 1

Describe chemical tests for water using cobalt(II) chloride

Answer 1

Blue anhydrous cobalt (II) chloride turns pink in the presence of water

Question 2

Describe chemical tests for water using copper(II) sulfate

Answer 2

White anhydrous copper (II) sulphate turns blue in the presence of water

Question 3

Describe, in outline, the treatment of the water supply in terms of filtration and chlorination

Answer 3

Untreated water is first pumped through large screens that filter out any large floating materials. The water is then passed through layers of coarse gravel and sand which remove any large, insoluble particles from the water. The water will now appear clean . However, there may still be microorganisms present in the water. Chlorine gas is bubbled through the water in the next stage of the treatment process. Chlorine is toxic to microorganisms and so any that are present in the water are killed. The water may now be slightly acidic so can be treated with an alkali to ensure that the water is neutral. The water is now safe to drink.

Question 4

Name some of the uses of water in the home

Answer 4

• drinking
• cooking
• plumbing
• heating
• dishwasher

Question 5

Name some of the uses of water in industry

Answer 5

• solvent
• coolent
• washing/cleaning
• to turn turbines

Question 6

Discuss the implications of an inadequate supply of water, limited to safe water for drinking and water for irrigating crops.

Answer 6

Inadequate water supplies would be unsafe to drink and will affect crop yield.

Question 7

State the composition of clean, dry air

Answer 7

78% nitrogen, 21% oxygen and the remainder as being a mixture of noble gases (such as argon 0.93%) and carbon dioxide (0.04%)

Question 8

Name the common pollutants in the air

Answer 8

carbon monoxide, sulfur dioxide, oxides of nitrogen and lead compounds

Question 9

State the source of carbon monoxide

Answer 9

Source is from the incomplete combustion of carbon-containing substances (leads to a poisonous gas which combines with haemoglobin in red blood cells)

Question 10

State the source of sulfur dioxide

Answer 10

Source is from the combustion of fossil fuels which contain sulfur compounds (leading to ‘acid rain’)

Question 11

State the source of oxides of nitrogen

Answer 11

Source is from car engines (leading to ‘acid rain’)

Question 12

State the source of lead compounds

Answer 12

Source is from leaded petrol (leading to cancer and brain injuries in children)

Question 13

State the conditions required for the rusting of iron

Answer 13

Oxygen and water needs to be present with iron

Question 14

Why are these common pollutants a global concern?

Answer 14

This is because these pollutants can be found to be produced around the world. it also enters the atmosphere which affects all countries, not just the ones producing a lot of pollution.

Question 15

Describe and explain methods of rust prevention

Answer 15

Oil or grease: When something is covered in oil it forms a protective layer that stops any oxygen or water to go through.
Painting: It prevents moisture from reaching the metal
Coating with plastic: It stops water and oxygen to reach the metal surface.
Plating with a non-reactive metal: It creates a physical barrier to oxygen and water. It also acts like a sacrifice metal.

Question 16

Describe the separation of oxygen and nitrogen from liquid air by fractional distillation

Answer 16

Air is filtered to remove impurities and then cooled so water vapour and CO2 are no longer a gas. They then remove the ice and CO2. The air is then cooled to -200˚C. Both nitrogen and oxygen are added to the bottom of the fractional distillation column where it gets slightly heated to turn into a gas. The nitrogen, having a lower boiling point, moves to the top and condenses whilst oxygen stays at the bottom. Their liquids are then collected.

Question 17

Describe and explain the presence of oxides of nitrogen in car engines and their catalytic removal

Answer 17

With the high temperature, nitrogen reacts with oxygen to from oxides of nitrogen. People use catalyst converters (with catalysts) to prevent the release of these oxides. What happens is the nitrogen oxides turn back into nitrogen and oxygen alone. Then carbon monoxide with the oxygen to form CO2. Nitrogen oxides and carbon monoxide then form nitrogen and CO2. Unburnt hydrocarbons are then converted into CO2 and water. Therefore, nitrogen oxides and carbon monoxide pass the platinum catalyst to form nitrogen, oxygen and carbon dioxide.

Question 18

Describe and explain sacrificial protection in terms of the reactivity series of metals and galvanising as a method of rust prevention

Answer 18

Sacrificial protection involves coating a metal with another more reactive metal, higher in the reactivity series. it protects the inside by corroding first, protecting the inner metal. An example is galvanising, where zinc is used to cover iron.

Question 19

Describe the need for nitrogen-, phosphorus- and potassium-containing fertilisers

Answer 19

Nitrates are needed for plants to make nutrients and increase the yield of crops, phosphorus helps convert nutrients nutrients into building blocks that help plants grow and increasing the quality of the plant and potassium helps plants become more resistant to disease and increases crop yield.

Question 20

Describe the displacement of ammonia from its salts

Answer 20

When ammonium salt reacts with a strong base, ammonia is produced with water and a different salt. An example is ammonium chloride reacting with sodium hydroxide.

Question 21

Describe and explain the essential conditions for the manufacture of ammonia by the Haber process including the sources of the hydrogen and nitrogen, i.e. hydrocarbons or steam and air

Answer 21

Haber process is an exothermic industrial process that goes through a reaction in order to produce fertilisers. the reaction is the following:
3H2 + N2 ⇌ 2NH3
Firstly, obtain hydrogen and nitrogen from natural gas, steam, hydrocarbons or air.
1. Nitrogen and hydrogen gas are pressured to 200 atm and heated to 450 °C.
2. The gases are passed over a catalyst (iron(III) oxide).
3. Inside the chamber, nitrogen and hydrogen combine to form ammonia.
4. Ammonia gas is condensed and removed.
(essential conditions are the 200 atm pressure, 450˚C and the iron catalyst)

Question 22

Give some example of greenhouse gases and how they affect the environment

Answer 22

Carbon dioxide and methane are examples of greenhouse gases. Greenhouse gases negatively affect the environment as they trap the heat of the sun and keep it in the atmosphere. This can lead to global warming and climate change.

Question 23

State the formation of carbon dioxide

Answer 23

• as a product of complete combustion of
  carbon-containing substances
• as a product of respiration
• as a product of the reaction between an acid and a carbonate
• from the thermal decomposition of a carbonate

Question 24

State the sources of methane

Answer 24

It includes the decomposition of vegetation and waste gases from digestion in animals. Most of them are produced by microbes that eat the vegetation outside and inside cows with methane as a waste.

Question 25

Describe the carbon cycle

Answer 25

Carbon dioxide produced by respiration with oxygen by living organisms are then released into the atmosphere where they are absorbed by the plants (even kept for storage underground for fossil fuels) and they produce oxygen from that carbon dioxide. Rinse and repeat and that is the carbon cycle. However combustion of the fossil fuels from the living organisms also produce a lot of CO2. Due to the industrial revolution, the percentage of CO2 in the atmosphere has increased.