A student plans to carry out an experiment to find the relative molecular mass, Mr, of a soluble acidic gas, X, by finding the mass of a measured volume of gas X. Gas X can be prepared by the reaction between concentrated sulfuric acid and copper. Two methods of gas collection are available to the student, as shown. [Figure 1.1]

1. (a)(i)Explain why the first sample of gas collected from either apparatus should not be used for the Mr determination of gas X.[1]
2. (a)(ii)Give two reasons, other than your answer to (a)(i), why, for this experiment, the apparatus in method A is less suitable than the apparatus in method B for collecting a sample of gas X. reason 1 reason 2[2]
3. (b)(i)The student is told to use the U-tube shown to find the mass of a sample of gas X. [Figure 1.2] A 100.0 cm³ sample of pure gas X is placed in a gas syringe. The gas syringe is attached to a U-tube containing small lumps of solid soda lime, a mixture of sodium hydroxide and calcium hydroxide. All of gas X is slowly passed into the U-tube and the mass of gas X absorbed determined. The temperature and the pressure of the room are recorded. State the measurements that are needed to determine the mass of gas X absorbed.[1]
4. (b)(ii)Suggest why soda lime is used to absorb gas X.[1]
5. (c)Gas X can cause respiratory distress. State an appropriate precaution that should be taken when doing this experiment.[1]
6. (d)(i)Experiment 1 is carried out at a temperature of 21°C, a pressure of 9.8 × 10⁴ Pa, and uses 100 cm³ of pure gas X. Calculate the number of moles of gas X present in Experiment 1. You should assume that gas X behaves like an ideal gas and so use PV = nRT. R = 8.31 JK⁻¹ mol⁻¹ moles of gas X =[2]
7. (d)(ii)The sample of gas X is found to have a mass of 0.251 g. Explain how the student should use this information and their results to determine the Mr of X.[1]
8. (d)(iii)Not all of gas X is absorbed by the soda lime. State what effect, if any, this has on the student's calculated value of the Mr of gas X.[1]
9. (d)(iv)In Experiment 2, the same mass of gas X is used, but the student did not record the temperature and pressure. The calculated Mr of X for Experiment 2 is higher than the value calculated by the student for Experiment 1. State and explain how the value of P/T changes from Experiment 1 to Experiment 2.[1]
10. (e)State how the reliability of the results in Experiment 1 could be improved.[1]
11. (f)A different gas, methylamine, is alkaline. State a change that would have to be made to the apparatus so that the Mr of methylamine could be determined.[1]

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