Chemistry Paper 2
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The amount of water vapour in today’s atmosphere is much less than the amount in the Earth’s early atmosphere. Explain why the amount of water vapour in the atmosphere has decreased.
• Earth temperatures cooled • water vapour condensed forming oceans
At the end of the experiment, the apparatus and its contents are allowed to cool before the final volume of gas is measured. The apparatus and its contents must be allowed to cool because
• The gas has expanded when it is hot
The Earth’s earliest rocks contained iron sulfide and no iron oxide. Later the rocks contained iron oxide as well as iron sulfide. Explain what happened to allow this change to occur.
• oxygen increased in atmosphere • iron is oxidised
Describe what you would see if damp, blue litmus paper is placed into chlorine gas.
• blue litmus first turns red • then it bleaches
Describe what is meant by a covalent bond.
• shaired pair of electrons
Explain why chlorine is a gas, rather than a liquid, at room temperature.
• has a low boiling point • intermolecular forces are weak and take little energy to break
When the gas hydrogen chloride, HCl, is dissolved in water, a solution forms. Blue litmus paper dipped in this solution turns red. State why the litmus paper turns red.
• solution is acidic (Has H+ ions)
Explain, in terms of electronic configurations, the increase in reactivity from lithium to sodium to potassium.
• outer electron becomes further from the nucleus • so outer electron more easily lost
Which of the following is a trend in a property of the fractions obtained from the top of the column to those obtained from the bottom?
• the viscosities increase
Explain why alkanes are described as hydrocarbons.
• compounds containing only carbon and hydrogen atoms
Describe what is seen when chlorine water is added to potassium bromide solution and the mixture shaken.
• potassium bromide solution colourless • mixture turns yellow
A solid ionic compound is dissolved in water to form a solution. Describe a simple experiment to show that charged particles are present in this solution.
• carry out electrolysis experiment • need a cathode and anode and power supply connected to it • need ammeter to show the current
State a change that can be made to the apparatus in Figure 6 to measure the volumes of gas more accurately.
• gas syringe
Calcium reacts with water to form calcium hydroxide, Describe what would be seen when a piece of calcium is dropped into a container of water.
• hydrogen produced as a gas so there would be bubbles • calcium hydroxide produced as a solid so the water would go cloudy
Calcium reacts with water to form calcium hydroxide, Describe what would be seen when a piece of calcium is dropped into a container of water.
• hydrogen produced as a gas so there would be bubbles • calcium hydroxide produced as a solid so the water would go cloudy
Fractions of crude oil contain alkanes. A sample of decane, C10H22, was cracked using the apparatus in Figure 4. This produced a mixture of products, including ethene. Explain how ethene is produced using the apparatus in Figure 4.
• when the decane is heated, turns to a gas • gas breaks down as it comes in contact with hot porous pot • large molecules of decane produce smaller molecules, including ethene
A student investigated the rate of reaction between dilute hydrochloric acid and marble chips (calcium carbonate). Calcium chloride, carbon dioxide and water are formed. Complete and balance the equation for the reaction.
• CaCO3 + 2HCl → CaCl2 + CO2 + H2O
The order of reactivity of chlorine, bromine and iodine can be determined by carrying out displacement reactions. Explain how displacement reactions can be used to show the reactivity of these three elements.
• order of reactivity: chlorine > bromine > iodine • add (aqueous) chlorine to a solution of potassium bromide, the solution turns orange/yellow • bromine is produced, Cl2 + 2KBr → Br2 + 2KCl • chlorine is more reactive, displaces bromine • add (aqueous) bromine to a solution of potassium iodide, the solution turns brown • iodine is produced, Br2 + 2KI → I2 + 2KBr • bromine is more reactive displaces iodine • add (aqueous) chlorine to a solution of potassium iodide, the solution turns brown • iodine is produced, Cl2 + 2KI → I2 + 2KCl • chlorine is more reactive, displaces iodine