AQA AS Jun 2016 Paper 1 Q3

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This question is about a white solid, MHCO3, that dissolves in water and reacts with hydrochloric acid to give a salt. MHCO3 + HClMCl + H2O + CO2 A student was asked to design an experiment to determine a value for the Mr of MHCO3. The student dissolved 1464 mg of MHCO3 in water and made the solution up to 250 cm3. 25.0 cm3 samples of the solution were titrated with 0.102 mol dm3 hydrochloric acid. The results are shown in Table 1. Table 1 Initial burette reading / cm3 Final burette reading / cm3 Titre / cm3 Rough 0.00 10.00 10.00 10.00 19.50 9.50 19.50 29.25 9.75 29.25 38.90 9.65 0 3 that reacted with 25.0 cm3 of the MHCO3 solution. . 1 Calculate the mean titre and use this to determine the amount, in moles, of HCl [3 marks] 0 3 . 2 Calculate the amount, in moles, of MHCO3 in 250 cm3 of the solution. Then calculate the experimental value for the Mr of MHCO3. Give your answer to the appropriate number of significant figures. [3 marks] *06* M/JUN16/7404/1<br /> 0 3 . 3 The student identified use of the burette as the largest source of uncertainty in the experiment. Using the same apparatus, suggest how the procedure could be improved to reduce the percentage uncertainty in using the burette. Justify your suggested improvement. [2 marks] Suggestion Justification 0 3 . 4 Another student is required to make up 250 cm3 of an aqueous solution that contains a known mass of MHCO3. The student is provided with a sample bottle containing the MHCO3. Describe the method, including apparatus and practical details, that the student should use to prepare the solution. [6 marks] *07* More answer space is available on page 8 Turn overM/Jun16/7404/1<br /> *08* M/JUN16/7404/1<br />

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