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9701/32

Chemistry 9701/32 — May/June 2014

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

3
questions
40
marks
120
minutes

Topics Analysis, Conclusions and Evaluation · Manipulation, Measurement and Observation · Presentation of Data and Observations · Qualitative Analysis

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationQualitative AnalysisFree sample

Carbon dioxide in the atmosphere dissolves in rain water making it acidic. When this water passes through limestone containing calcium carbonate, it forms solutions of calcium hydrogen carbonate.

In this experiment, you will determine the concentration of hydrogen carbonate ions in a solution by titration with hydrochloric acid.

FB 1 is 0.100 mol dm−30.100\text{ mol dm}^{-3} hydrochloric acid, HCl\text{HCl}.
FB 2 contains an unknown concentration of hydrogen carbonate ions, HCO3−\text{HCO}_3^-.
methyl orange indicator

(a)

Method

  • Fill the burette with FB 1.
  • Pipette 25.0 cm325.0\text{ cm}^3 of FB 2 into a conical flask.
  • Add a few drops of methyl orange indicator to the conical flask.
  • Perform a rough titration and record your burette readings in the space below.

The rough titre is ....................... cm3\text{cm}^3.

  • Carry out as many accurate titrations as you think necessary to obtain consistent results.
  • Make certain any recorded results show the precision of your practical work.
  • Record, in a suitable form below, all of your burette readings and the volume of FB 1 added in each accurate titration.
7M
(b)

From your accurate titration results obtain a suitable value to be used in your calculations. Show clearly how you obtained this value.

25.0 cm325.0\text{ cm}^3 of FB 2 required ........................ cm3\text{cm}^3 of FB 1.

1M
(c)

Calculations

Show your working and appropriate significant figures in the final answer to each step of your calculations.

2M
(i)

Calculate the number of moles of hydrochloric acid present in the volume of FB 1 calculated in (b).

moles of HCl\text{HCl} = ........................ mol

(ii)

Write the ionic equation for the reaction of FB 1 with FB 2.

(iii)

Calculate the concentration, in mol dm−3\text{mol dm}^{-3}, of hydrogen carbonate ions in FB 2.

concentration of HCO3−\text{HCO}_3^- in FB 2 = ........................ mol dm−3\text{mol dm}^{-3}

The rest of this paper

2 more questions
  • Q2Presentation of Data and Observations · Analysis, Conclusions and Evaluation12M
  • Q3Qualitative Analysis · Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation18M
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