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9701/35

Chemistry 9701/35 — May/June 2016

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

3
questions
40
marks
120
minutes

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

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsFree sample

In this experiment you will determine the concentration of a solution of sulfuric acid by titration.

FA 1 is sulfuric acid, H2SO4\text{H}_2\text{SO}_4.
FA 2 is aqueous sodium hydroxide, containing 4.20 g NaOH4.20\text{ g NaOH} dissolved in 1.00 dm31.00\text{ dm}^3 of water.
thymolphthalein indicator

(a)

Method

Dilution of FA 1

  • Pipette 10.0 cm310.0\text{ cm}^3 of FA 1 into the 250 cm3250\text{ cm}^3 volumetric flask.
  • Make the solution up to the mark using distilled water.
  • Shake the flask thoroughly.
  • This diluted solution of sulfuric acid is FA 3. Label the flask FA 3.

Titration

  • Fill the burette with FA 2.
  • Pipette 25.0 cm325.0\text{ cm}^3 of FA 3 into a conical flask.
  • Add a few drops of thymolphthalein indicator.
  • Perform a rough titration and record your burette readings in the space below. The end point is reached when the solution turns a permanent pale blue colour.

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

  • Carry out as many accurate titrations as you think necessary to obtain consistent results.
  • Make sure 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 FA 2 added in each accurate titration.

Keep solution FA 1 for use in Questions 2 and 3.

7M
(b)

From your accurate titration results, obtain a suitable value for the volume of FA 2 to be used in your calculations.
Show clearly how you obtained this value.

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

1M
(c)

Calculations

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

5M
(i)

Calculate the number of moles of sodium hydroxide present in the volume of FA 2 calculated in (b).
Use the data in the Periodic Table on page 16.

moles of NaOH=............................. mol\text{moles of NaOH} = ............................. \text{ mol}
(ii)

Complete the equation for the reaction of sulfuric acid with sodium hydroxide. State symbols are required.

............................+............................→...... Na2SO4(aq)+...........................\text{............................} + \text{............................} \rightarrow \text{...... Na}_2\text{SO}_4\text{(aq)} + \text{...........................}
(iii)

Use your answers to (i) and (ii) to calculate the number of moles of sulfuric acid used in each titration.

moles of H2SO4=............................. mol\text{moles of H}_2\text{SO}_4 = ............................. \text{ mol}
(iv)

Calculate the concentration, in mol dm−3\text{mol dm}^{-3}, of sulfuric acid in FA 3.

concentration of H2SO4 in FA 3=............................. mol dm−3\text{concentration of H}_2\text{SO}_4\text{ in FA 3} = ............................. \text{ mol dm}^{-3}
(v)

Calculate the concentration, in mol dm−3\text{mol dm}^{-3}, of sulfuric acid in FA 1.

concentration of H2SO4 in FA 1=............................. mol dm−3\text{concentration of H}_2\text{SO}_4\text{ in FA 1} = ............................. \text{ mol dm}^{-3}

The rest of this paper

2 more questions
  • Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation14M
  • Q3Qualitative Analysis13M
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