Questions with one to four marks usually start with command words. If a question starts with the command word 'state', 'give', 'name' or 'write down', it needs a short answer only. This type of question can often be answered with one word or phrase.
It is important to state, give, name or write down the number of things that the question asks for. If you write down fewer, you cannot get all the marks. If you write down more, and one is wrong, you might lose a mark.
Some questions start with the command words 'describe', 'explain' or 'compare'. These are often worth two or more marks:
More complex structured questions will be worth three or four marks. They include questions with complex descriptions and explanations, and questions in which you need to compare things.
Some of the answers are shown here as bullet points. This is to show clearly how a mark can be obtained. However, do not use bullet points in your answers - the points must be linked together logically.
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The rate of the reaction between dilute acid and calcium carbonate can be investigated by doing the reaction on a top pan balance and measuring the change in mass every ten seconds. Use the symbol equation below to explain why there is a loss in mass during this reaction.
2HCl(aq) + CaCO3(s) → CaCl2(aq) + H2O(l) + CO2(g) [2 marks]
A gas is produced 
Which escapes from the flask 
Describe an alternative way of measuring the rate of the above reaction, which does not involve measuring the mass change of the reaction. [2 marks]
Collect the gas in a gas syringe or inverted measuring cylinder in a water bath 
Measure the volume of gas produced every ten seconds 
Explain, in terms of particles, why the rate decreases during the reaction between magnesium and hydrochloric acid. [2 marks]
The concentration of acid decreases over time 
So collisions are less frequent 
The equation below shows one stage in the manufacture of sulfuric acid from sulfur dioxide.
2SO2(g) + O2(g) ⇌ 2SO3(g)
The reaction is exothermic in the forward direction.
Use le Chatelier's principle to predict the effect of increasing the temperature on the amount of sulfur trioxide (SO3) produced at equilibrium. Give a reason for your answer. [2 marks]
Because the position of equilibrium moves to the left, in the endothermic direction, to counteract the increase in temperature.