The particle model - Six-mark questions

Six-mark questions are often the questions that people find the most difficult. In all longer answer questions, but especially the six-mark ones, it is important that you plan your answer and not just rush into it. After all, you would plan an essay or short story before starting. Without a plan it is easy to stray away from the key point and lose marks, get steps in a process in the wrong order or forget key bits of information.

Six-mark questions will start with command words such as 'describe' or 'explain'. The command words 'describe' and 'explain' can be confusing. If you are asked to describe a graph, you will be expected to write about its overall shape, whether it is linear or curved, the slope of gradients etc. If you are asked to explain why a pattern or trend is seen in a graph, you will be expected to use your science knowledge not just say what you see (which is a description), eg The graph shows the number of radioactive nuclei decreases as time increases. It does this because…

Explain how and why questions often have the word 'because' in their answer. Describe questions don't.

The number of marks per question part is given in this form '[6 marks]'. It is essential that you give as many different points in your answer as possible, linking these together. Often, you will be asked to compare two things, make sure that you include both in your answer otherwise, you are likely to limit your score to two marks out of six marks.

Edexcel questions courtesy of Pearson Education Ltd.

Sample question 1 - Foundation and Higher

Question

Describe how the student should carry out an experiment to determine the specific heat capacity of water. [6 marks]

Plan the key points that you should include in your answer. Consider the measurements you would take and indicate what equipment you would use to take them. State the equations you need to use to calculate the energy supplied to the heater and the specific heat capacity of water.

For example:

Use an insulated beaker full of water. The insulation reduces heat loss. Use a top pan balance to measure the mass of the empty beaker and then the beaker and water. Calculate the mass of the water by subtracting. Measure the temperature of the water before heating using a thermometer. Use a heater with an ammeter connected in series to measure the current in the heater and a voltmeter in parallel with the heater to measure the pd. Record the time the heater is on and measure the end temperature of the water. Use E = I \times V \times t to determine energy supplied to the Water. Use \Delta E = m \times c \times \Delta \theta to determine the specific heat capacity of the water.

Sample question 2 - Higher

Question

When a diver is swimming under water, she breathes out bubbles of gas.

The bubbles of gas rise to the surface. The temperature of the gas does not change. Explain what happens to a bubble as it rises to the surface. Your answer should refer to gas equations, kinetic theory and particles. [6 marks]

Plan the key points that you should include in your answer. You will need to discuss the origin of pressure in terms of kinetic theory and the movements of molecules.

For example:

The bubbles get bigger as they rise. Molecules of gas are in constant motion, they are widely spaced and moving randomly. The molecules impact on surface of bubble and the average of all the impacts produces gas pressure. So the pressure is due to rate at which gas particles collide with bubble surface. For the bubble to be stable the inward pressure from the liquid must equal outward the pressure from the gas. Liquid pressure decreases as bubble rises so the gas pressure must decrease as it rises too. Since P_1 V_1 = P_2 V_2, if the gas pressure decreases the volume of bubble must increase.