6) A student carries out an experiment to identify an unknown carbonate.
â€¢ The student weighs a sample of the solid carbonate in a weighing bottle.
â€¢ The student tips the carbonate into a beaker and weighs the empty weighing bottle.
â€¢ The student prepares a 250.0 cm3 solution of the carbonate.
â€¢ The student carries out a titration using 25.0 cm3 of this solution measured using a pipette with0.100 mol dmâˆ’3 hydrochloric acid in the burette.
(a) The sample of carbonate is dissolved in approximately 100 cm3 of distilled water in a beaker and thesolution transferred to a volumetric flask. The volume of the solution is made up to 250.0 cm3 withdistilled water.
The student carries out the final part of the experiment by adding 0.100 mol dmâˆ’3 hydrochloric acidto a burette and performing a titration using a 25.0 cm3 sample of the aqueous carbonate. The titre is 22.20.
The equation below represents the reaction between the carbonate and hydrochloric acid.
M2CO3(aq) + 2HCl(aq) â†’ 2MCl(aq) + CO2(g) + H2O(l)
(i) Calculate the amount, in mol, of M2CO3 used in the titration.
ii) The studentâ€™s mass readings are recorded below.
Mass of weighing bottle + carbonate / g 14.92
Mass of weighing bottle / g 13.34
Use the studentâ€™s results to identify the carbonate, M2CO3.
The answer for (i) was 0.00111. How? I can do (ii) obviously if I knew the answer to (i) because that's just rearranging n=M/mr.
So can someone please explain how to get the answer? Thanks.
That's the paper and the mark scheme is on the bottom - question 6.
Titration and moles question
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