C1 Earth Chemistry

Limestone

Limestone is a rock made mainly of calcium carbonate (CaCO 3 ) It was formed from the remains of animals millions of years ago and can be quarried Limestone can be heated with clay to make cement Cement is mixed with sand to make mortar Cement is mixed with water, sand and crushed rock to produce concrete Heating limestone breaks it down – this is thermal decomposition Calcium carbonate  calcium oxide + carbon dioxide CaCO 3  CaO + CO 2

Past paper questions Do question 2 Foundation tier – do q.3 Higher tier – do q.4 you have 3 minutes

Carbonates Buildings made of limestone are damaged by acid rain When this happens, carbon dioxide is given off Carbon dioxide turns limewater cloudy The carbonates of magnesium, copper, zinc, calcium and sodium can be thermally decomposed too They always form a metal oxide and carbon dioxide e.g. Magnesium carbonate  magnesium oxide + carbon dioxide MgCO 3  MgO + CO 2

Uses of calcium oxide When limestone is thermally decomposed it produces calcium oxide When calcium oxide is added to water it produces calcium hydroxide Calcium hydroxide can be filtered to produce limewater Calcium hydroxide is an alkali. It can be used to neutralise acids. It is used by farmers to neutralise acidic soil, and to neutralise acidic industrial gases.

Past paper questions Do questions 7 & 8 You have 8 minutes

Changes in the Earth and its atmosphere

Structure of the Earth The Earth is made up of many layers The Earth is surrounded by the atmosphere Crust: thin and rocky Mantle: flowing rock Core: mixture of nickel and iron (inner core = solid outer core = liquid)

Tectonic plates The crust and mantle are broken up into large pieces (tectonic plates) They move a few centimetres per year due to convection currents in the mantle Earthquakes are caused when plate boundaries meet and push together

Past paper questions A newspaper reported that an earthquake off the coast of Kent had caused plaster to come down from ceilings, house tiles to loosen and church bells to ring. (a) Suggest why the earthquake in Kent was reported and why most earthquakes in the UK are not reported.(2) (b) Explain how earthquakes are caused.(3) (c) People living in Kent were not warned about this earthquake. In terms of what is happening within the Earth, explain the problems of trying to predict earthquakes.(2) (Total 7 marks)

Answer (a) (Kent reported because) damage was caused or it was above 3 (on the Richter scale) accept description of damage (1) (others not reported because) no vibrations / not felt / not noticed (allow below 3 (on Richter scale)) ignore no damage (1) (b) movement of (tectonic) plates (allow collision of plates or plates rubbing together or plates pushing against each other) (1) any two from: vibration / (shock)waves (in the earth) or p and s waves (accept sudden jolts / slips) caused by convection currents (in the mantle) heat / energy released from radioactive processes

Answer (continued) (c) any two from: scientists do not know: what happens under the crust / mantle / under the surface (accept anything under the crust) where forces / pressures are building up how to measure these forces / pressures when these forces / pressures reach their limit (accept there is no pattern; ignore random / speed of movement) (2)

The modern atmosphere The Earth’s atmosphere has been the same for about 200 million years

The early atmosphere There are lots of theories One suggests that there was intense volcanic activity about 4.5 billion years ago when the Earth formed This released carbon dioxide, water vapour and nitrogen gas – this formed the first atmosphere The water vapour condensed and fell as rain, this formed the first oceans When life evolved plants released oxygen The amount of oxygen in the atmosphere increased and animals could evolve

Carbon Most of the carbon dioxide from the Earth’s early atmosphere has been taken up by plants, which were eaten by animals, which were turned to sedimentary rocks This means that most of the carbon is ‘locked’ in rocks and in fossil fuels Carbon dioxide also dissolved in oceans Over the past 200 million years the amount of carbon dioxide in the atmosphere has not changed much

The carbon cycle Using fossil fuels is increasing the amount of carbon in the atmosphere again

Past paper question Billions of years ago, the Earth’s early atmosphere was probably like the atmosphere of Venus today. The table shows a comparison of the atmospheres of the Earth and Venus today. Percentage composition of atmosphere Name of gas Earth today Venus today Nitrogen Oxygen 21 a trace Argon 0.97 a trace Carbon dioxide Average surface temperature 20 ºC 460 ºC (a) Use the names of gases from the table to complete the sentences. (i) In the Earth’s atmosphere today, the main gas is (1) (ii) In the Earth’s atmosphere billions of years ago, the main gas was (1) (b) (i) Scientists do not know the accurate composition of the Earth’s early atmosphere. Suggest why. (1) (ii) Use information from the table to answer this question. Water vapour is present in the atmospheres of the Earth and Venus today. The Earth’s surface is mainly covered by water. Suggest why there is no water on the surface of Venus. (1)

Answer (a) (i) nitrogen / N 2 1 (ii) carbon dioxide / CO 2 1 (b) (i) humans / scientists had not evolved accept it was billions / millions of years ago allow too long ago 1 (ii) temperature is above 100°C or any water would evaporate / boil accept Venus is too hot1