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9701/36

Chemistry 9701/36 — October/November 2019

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 ObservationsAnalysis, Conclusions and EvaluationFree sample

Quantitative Analysis

Read through the whole method before starting any practical work. Where appropriate, prepare a table for your results in the space provided.

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

1 Limewater is a saturated solution of calcium hydroxide, Ca(OH)2\text{Ca(OH)}_2, in water. In this experiment you will determine the concentration of limewater by titration with hydrochloric acid.

FB 1 is limewater.
FB 2 is 0.500 mol dm−30.500\text{ mol dm}^{-3} hydrochloric acid, HCl\text{HCl}.
bromophenol blue indicator

(a)

Method

Dilution of FB 2

  • Pipette 25.0 cm325.0\text{ cm}^3 of FB 2 into the 250 cm3250\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 FB 3. Label the volumetric flask FB 3.
  • Rinse the pipette thoroughly.

Titration

  • Fill the burette with FB 3.
  • Pipette 25.0 cm325.0\text{ cm}^3 of FB 1 into a conical flask.
  • Add a few drops of bromophenol blue.
  • 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 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 FB 3 added in each accurate titration.
7M
(b)

From your accurate titration results, obtain a suitable value for the volume of FB 3 to be used in your calculations.
Show clearly how you obtained this value.

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

1M
(c)

Calculations

(i)

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

1M
(ii)

Calculate the number of moles of hydrochloric acid, HCl\text{HCl}, in the volume of FB 3 calculated in (b).

moles of HCl=.............................. mol\text{moles of HCl} = \text{.............................. mol}
1M
(iii)

Give the equation for the reaction of calcium hydroxide with hydrochloric acid.

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

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

moles of Ca(OH)2=.............................. mol\text{moles of Ca(OH)}_2 = \text{.............................. mol}
1M
(iv)

Calculate the concentration, in mol dm−3\text{mol dm}^{-3}, of calcium hydroxide in FB 1.

concentration of Ca(OH)2 in FB 1=............................... mol dm−3\text{concentration of Ca(OH)}_2\text{ in FB 1} = \text{............................... mol dm}^{-3}
1M
(v)

Calculate the mass of calcium hydroxide dissolved in 1.00 dm31.00\text{ dm}^3 of limewater, FB 1.

mass of Ca(OH)2=............................... g\text{mass of Ca(OH)}_2 = \text{............................... g}
1M

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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