C2

Question 1

Describe the structure of the Earth

Answer 1

The Earth has a layered structure made up of the core, mantle and crust. The crust and upper part of the mantle is broken into large pieces called tectonic plates. These move slowly over the mantle.

Question 2

Explain how seismic waves are used to study the Earth’s structure.

Answer 2

S-waves can travel through the mantle, which shows that it’s solid. S-waves can only travel through solids. S-waves not detected in outer core’s shadow, suggesting is is liquid. - P-waves travel faster through the middle of the core, suggesting the inner core is solid.

Question 3

Describe the different between runny and thick lava.

Answer 3

Different types of igneous rocks form lava (molten rock on the Earth’s surface): basalt is rich in iron - it formed from runny lava produced in a fairly safe volcanic eruption, rhyolite is rich in silica - it formed from thick lava produced in an explosive eruption.

Question 4

Explain why geologists study volcanoes.

Answer 4

Geologists study volcanoes to try to predict future eruptions, and to gather information about the Earth’s structure.

Question 5

Name the main construction materials to substances found in the Earth’s crust

Answer 5

Granite, limestone and marble are used as construction materials. Cement, which is made from limestone, is used to make concrete. However reinforced concrete has better properties for construction work than concrete alone.

Question 6

Compare hardness of limestone, marble and granite.

Answer 6

Granite is much harder than marble, which is much harder than limestone.

Question 7

What is a balanced symbol equations to describe the thermal decomposition of limestone?

Answer 7

calcium carbonate –> calcium oxide + carbon dioxide CaCO3 –> CaO + CO2 copper(II) carbonate –> copper(II) oxide + carbon dioxide CuCO3 –> CuO + CO2

Question 8

How is cement made?

Answer 8

Cement and concrete are made from limestone, cement is made by heating powdered limestone with clay, concrete is made by mixing cement with sand, water and aggregate (crushed rock). Chemical reactions happen in the mixtures and eventually they set hard.

Question 9

What equipment is needed for electrolysis?

Answer 9

See Diagram below.

Question 10

Explain the advantages of recycling copper.

Answer 10

The world is running out of ores that are rich in copper.The recycling of copper is cheaper, and uses less energy and resources than extracting fresh copper from its ores.

Question 11

Name the main metals in amalgams, brass and solder

Answer 11

amalgam - mercury, brass - copper and zinc, solder - lead and tin.

Question 12

Define an alloy.

Answer 12

An alloy is a mixture of two elements, one of which is a metal. Alloys often have more useful properties than the metals they contain.

Question 13

How does salt water and acid rain affect rusting.

Answer 13

Iron and steel rust when they come into contact with water and oxygen. They rust faster in salty water or acid rain. Aluminium, on the other hand, does not corrode easily, because its surface is protected by a layer of aluminium oxide.

Question 14

Describe how rusting happens.

Answer 14

Iron and steel rust when they come into contact with water and oxygen. Both water and oxygen are needed for rusting to occur. In the experiment below, the nail does not rust when air or water is not present. Remember that 21 per cent of the air is oxygen. Rusting is an oxidation reaction. The iron reacts with water and oxygen to form hydrated iron(III) oxide, which we see as rust.

Question 15

Explain why aluminium does not corrode

Answer 15

Unlike iron and steel, aluminium does not rust or corrode in moist conditions. Its surface is protected by a natural layer of aluminium oxide. This prevents the metal below from coming into contact with air and oxygen. The layer of aluminium oxide does not flake off, unlike rust which can flake off the surface of iron and steel objects.

Question 16

Describe advantages and disadvantages of building cars from aluminium and steel

Answer 16

Aluminium has some advantages over steel. Since it has a lower density than iron or steel, a car body made from aluminium will be lighter than the same car body made from steel. This results in improved fuel economy. Also, aluminium does not corrode easily, so a car body made from aluminium will corrode less than one made from steel. It should last longer as a result. However, aluminium is more expensive than steel. So a car made from aluminium is likely to be more expensive than one made from steel.

Question 17

Describe the conditions needed to make ammonia in the Haber process and construct the balanced symbol equation.

Answer 17

The raw materials for this process are hydrogen and nitrogen: hydrogen is obtained by reacting natural gas with steam, or from cracking oil fractions, nitrogen is obtained from the air. In the Haber process, nitrogen and hydrogen react together under these conditions: a high temperature - about 450ºC a high pressure an iron catalyst.

Question 18

Describe neutralisation and recall the word equation.

Answer 18

When an alkali is added to an acid the pH of the mixture rises. This is because the alkali reacts with the acid to form neutral products. The reverse situation also happens too: when an acid is added to an alkali the pH of the mixture falls. This is because the acid reacts with the alkali to form neutral products. A reaction in which acidity or alkalinity is removed is called neutralisation. A neutralisation involving an acid and a base (or alkali) always produces salt and water. acid + base –> a salt + water

Question 19

Explain how metal oxides and hydroxides, and carbonates react with acid, and construct word equations.

Answer 19

Carbonates also neutralise acids. As well as a salt and water, carbon dioxide is also produced. The name of the salt can be predicted in just the same way. For example: hydrochloric acid + potassium carbonate –> potassium chloride + water + carbon dioxide

Question 20

Predict the names of salts from laboratory acids

Answer 20

The name of the salt produced in a neutralisation reaction can be predicted. The first part of the name is ‘ammonium’ if the base used is ammonia. Otherwise, it is the name of the metal in the base. The second part of the name comes from the acid used: chloride, if hydrochloric acid is used, nitrate, if nitric acid is used, sulfate, if sulfuric acid is used, phosphate, if phosphoric acid is used.

Question 21

Explain why fertilisers need to be soluble to be absorbed by plants

Answer 21

Fertilisers make crops grow faster and bigger so that crop yields are increased. They are water-soluble minerals. They must be able to dissolve in water so that plants can absorb them through their roots.

Question 22

Identify arguments for and against using fertilisers

Answer 22

The world population is increasing all the time, so more food has to be produced. Without fertilisers the yields of crops would be reduced. However, if too much fertiliser is used it can pollute water supplies. It may also lead to eutrophication, a situation where there is not enough oxygen dissolved in the water for aquatic organisms to survive.

Question 23

Predict the names of the acids and alkalis needed to make different fertilisers

Answer 23

Most fertilisers are made by the reaction of an acid and an alkali. The table shows some examples.

Question 24

Describe how salt can be mined as rock salt if extracted by solution mining

Answer 24

Salt can also be mined by solution mining. This happens in Cheshire in the North West of England. Water is pumped underground and into the salt deposit. Salt dissolves in the water, forming a concentrated salt solution. This is then pumped up to the surface ready for use by the chemical industry. Solution mining is a continuous process that is safer than sending miners underground.

Question 25

Explain how mining can cause subsidence

Answer 25

Mining for salt can lead to subsidence. This happens when insufficient salt is left underground after mining. The weight of the ground above causes the ground to sink downwards and this subsidence can damage buildings and roads.

Question 26

Recall the products of brine electrolysis

Answer 26

During electrolysis: chlorine gas forms at the anode (positive electrode) hydrogen gas forms at the cathode (negative electrode) a solution of sodium hydroxide forms. These products are reactive, so it is important to use inert (unreactive) materials for the electrodes.

Question 27

Describe how household bleach is made by reacting sodium hydroxide and chlorine

Answer 27

Household bleach, sodium chlorate, is made when sodium hydroxide and chlorine react together: sodium hydroxide + chlorine _ sodium chloride + water + sodium chlorate 2NaOH + Cl2 –> NaCl + H2O + NaClO Household bleach is used to clean and disinfect toilets, drains and kitchen surfaces.

Question 28

Describe the development of
plate tectonic theories.

Answer 28

The theory of plate tectonics and continental drift was proposed at the beginning of the last century by German scientist, Alfred Wegener.

Wegener suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold. For example, the Himalayas were formed when India came into contact with Asia. It took more than 50 years for Wegener’s theory to be accepted, because:

• it was difficult to work out how whole continents could move
• it was not until the 1960s that enough evidence was discovered to support the theory fully.

Question 29

Explain why reinforced concrete is a
better construction material

Answer 29

Reinforced concrete is a composite material made from concrete and steel. It is a better construction material than concrete alone because:

• concrete is hard and strong when squashed, but weak when stretched
• steel is flexible and strong when stretched.

The composite material combines the best properties of both materials, so that it is hard and strong when squashed or stretched. This makes it useful for building bridges.

Question 30

Explain how the use of ‘smart alloys’
like nitinol for spectacle frames have
increased alloy applications.

Answer 30

Smart alloys have unusual properties. Nitinol is an alloy of nickel and titanium, and is known as a shape memory alloy. If nitinol is bent out of shape, it returns to its original shape when it is either heated or an electric current is passed through it. This property makes it useful for making spectacle frames - they return to their original shape if they are put in hot water after they have been bent.

Question 31

Explain neutralisation in
terms of H+ + OH– ➝ H2O

Answer 31

Ions in solution

• acids in solution contain hydrogen ions, H+.
• alkalis in solution contain hydroxide ions, OH-.

Neutralisation can be written as an ionic equation:

Question 32

Explain the process of eutrophication

Answer 32

See image below.

Question 33

Describe in detail the preparation
of a named synthetic fertiliser
by the reactions of an acid
and an alkali.

Answer 33

The name or formula of a compound often suggests which elements are provided by a particular fertiliser. The table shows some examples.

The preparation of a fertiliser in a lab involves the following equipment:

• a measuring cylinder to measure a particular volume of an alkali solution
• a burette to add acid a little at a time until the alkali has been neutralised
• a filter funnel to remove solid crystals of fertiliser after evaporating some of the water from the neutral fertiliser solution.