AI SearchTopicalsYearlysNotesDashboardPricing
9701/33

Chemistry 9701/33 — February/March 2021

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.

In this experiment you will carry out a titration to identify the Group 1 metal, M, present in a metal hydrogencarbonate, MHCO3\text{MHCO}_3.

FA 1 is 0.0550 mol dm−30.0550\text{ mol dm}^{-3} sulfuric acid, H2SO4\text{H}_2\text{SO}_4.
FA 2 is the metal hydrogencarbonate, MHCO3\text{MHCO}_3.
bromophenol blue indicator

(a)

Method

Preparing a solution of FA 2

  • Weigh the stoppered container of FA 2. Record the mass in the space below.
  • Tip all the FA 2 into the beaker.
  • Reweigh the container with its stopper. Record the mass.
  • Calculate and record the mass of FA 2 used.
  • Add approximately 100 cm3100\text{ cm}^3 of distilled water to FA 2 in the beaker.
  • Stir the mixture with a glass rod until all the FA 2 has dissolved.
  • Transfer this solution into the 250 cm3250\text{ cm}^3 volumetric flask.
  • Wash the beaker with distilled water and transfer the washings to the volumetric flask.
  • Rinse the glass rod with distilled water and transfer the washings to the volumetric flask.
  • Make up the solution in the volumetric flask to the mark using distilled water.
  • Shake the flask thoroughly.
  • This solution of MHCO3\text{MHCO}_3 is FA 3. Label the flask FA 3.

Titration

  • Fill the burette with FA 1.
  • Pipette 25.0 cm325.0\text{ cm}^3 of FA 3 into a conical flask.
  • Add a few drops of bromophenol blue 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 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.
8M
(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 cm325.0\text{ cm}^3 of FA 3 required .............................. cm3\text{cm}^3 of FA 1.

1M
(c)

Calculations

(i)

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

1M
(ii)

Calculate the number of moles of sulfuric acid present in the volume of FA 1 calculated in (b).

moles of H2SO4=.............................. mol\text{moles of H}_2\text{SO}_4 = \text{.............................. mol}
1M
(iii)

Complete the equation for the reaction of sulfuric acid and MHCO3\text{MHCO}_3.
State symbols are not required.

.....MHCO3+.....H2SO4→.....M2SO4+....................+....................\text{.....MHCO}_3 + \text{.....H}_2\text{SO}_4 \rightarrow \text{.....M}_2\text{SO}_4 + \text{....................} + \text{....................}

Use your answer to (c)(ii) to deduce the number of moles of MHCO3\text{MHCO}_3 used in each titration.

moles of MHCO3=.............................. mol\text{moles of MHCO}_3 = \text{.............................. mol}
1M
(iv)

Use your answer to (c)(iii) and your data on page 2 to calculate the relative formula mass, MrM_r, of MHCO3\text{MHCO}_3.

Mr of MHCO3=..............................M_r \text{ of MHCO}_3 = \text{..............................}
1M
(v)

Calculate the relative atomic mass, ArA_r, of M.

Ar of M=..............................A_r \text{ of M} = \text{..............................}

Suggest the identity of M.

M is .............................. .

1M
(d)
(i)

A student used a pipette that was labelled 25.0±0.06 cm325.0 \pm 0.06\text{ cm}^3 to measure FA 3.

Show how you calculate the maximum percentage error in the volume of FA 3.

1M
(ii)

The student suggested that it would have been more accurate to measure the volume of FA 3 with a burette instead of the pipette.

State and explain whether you agree with the student.

1M

The rest of this paper

2 more questions
  • Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Qualitative Analysis · Analysis, Conclusions and Evaluation12M
  • Q3Qualitative Analysis12M
Loading the full paper…