Chemistry 9701/33 — October/November 2019

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

questions

marks

120

minutes

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

Q1Manipulation, Measurement and ObservationAnalysis, Conclusions and EvaluationPresentation of Data and ObservationsFree sample

In this experiment you will determine the concentration of a solution of hydrochloric acid by titration with an alkali.

FA 1 is a solution containing $6.00\text{ g dm}^{-3}$ of sodium hydroxide, $\text{NaOH}$ .
FA 2 is hydrochloric acid, $\text{HCl}$ . (This solution is also used in Questions 2 and 3.)
methyl orange indicator

(a)

Method

Dilution of FA 2

Pipette $10.0\text{ cm}^3$ of FA 2 into the $250\text{ cm}^3$ volumetric flask.
Make the solution up to the mark using distilled water.
Shake the solution in the volumetric flask thoroughly.
This solution of hydrochloric acid is FA 3. Label the volumetric flask FA 3.

Titration

Fill the burette with FA 1.
Pipette $25.0\text{ cm}^3$ of FA 3 into a conical flask.
Add several drops of methyl orange indicator.
Perform a rough titration and record your burette readings in the space below.

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

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 1 added in each accurate titration.

(b)

From your accurate titration results, obtain a suitable value for the volume of FA 1 to be used in your calculations.
Show clearly how you obtained this value.

$25.0\text{ cm}^3$ of FA 3 required .............................. $\text{cm}^3$ of FA 1.

(c)

Calculations

(i)

Give your answers to (ii), (iii) and (iv) to the appropriate number of significant figures.

(ii)

Calculate the number of moles of sodium hydroxide, $\text{NaOH}$ , in the volume of FA 1 calculated in (b).

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

(iii)

Write the equation for the neutralisation of hydrochloric acid with sodium hydroxide. Include state symbols.

.............................................................................................................................................

Deduce the number of moles of hydrochloric acid that reacted with the sodium hydroxide in (ii).

\text{moles of hydrochloric acid} = \text{...................... mol}

(iv)

Calculate the concentration, in $\text{mol dm}^{-3}$ , of hydrochloric acid in FA 2.

\text{concentration of HCl in FA 2} = \text{.............................. mol dm}^{-3}

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2 more questions

Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation16M
Q3Qualitative Analysis · Analysis, Conclusions and Evaluation · Manipulation, Measurement and Observation11M

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