Edexcel Jan 2011 Paper 1 Q16

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PMT 16 (a) Coral reefs are produced by living organisms and predominantly made up of calcium carbonate. It has been suggested that coral reefs will be damaged by global warming because of the increased acidity of the oceans due to higher concentrations of carbon dioxide. (i) Write a chemical equation to show how the presence of carbon dioxide in water results in the formation of carbonic acid. State symbols are not required. (ii) Write the ionic equation to show how acids react with carbonates. State symbols are not required. (1) (2) *N37962A01124* 11 Turn over<br /> (b) One method of determining the proportion of calcium carbonate in a coral is to dissolve a known mass of the coral in excess acid and measure the volume of carbon dioxide formed. In such an experiment, 1.13 g of coral was dissolved in 25 cm3 of hydrochloric acid (an excess) in a conical flask. When the reaction was complete, 224 cm3 of carbon dioxide had been collected over water using a 250 cm3 measuring cylinder. (i) Draw a labelled diagram of the apparatus that could be used to carry out this experiment. (ii) Suggest how you would mix the acid and the coral to ensure that no carbon dioxide escaped from the apparatus. PMT (2) (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (iii) Calculate the number of moles of carbon dioxide collected in the experiment. [The molar volume of any gas is 24 000 cm3 mol1 at room temperature and pressure.] (1) 12 *N37962A01224*<br /> PMT (iv) Complete the equation below for the reaction between calcium carbonate and hydrochloric acid by inserting the missing state symbols. CaCO3(. . . . . . . . . . . . . .) + 2HCl(. . . . . . . . . . . . . .) (cid:111) CaCl2(. . . . . . . . . . . . . .) + H2O(l) + CO2(. . . . . . . . . . . . . .) (v) Calculate the mass of 1 mol of calcium carbonate. [Assume relative atomic masses: Ca = 40, C = 12, O = 16.] (1) (1) (vi) Use your data and the equation in (iv) to calculate the mass of calcium carbonate in the sample and the percentage by mass of calcium carbonate in the coral. Give your final answer to three significant figures. (2) (1) (vii) When this experiment is repeated, the results are inconsistent. Suggest a reason for this other than errors in the procedure, measurements or calculations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Total for Question 16 = 12 marks) *N37962A01324* 13 Turn over<br />

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