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9701/34

Chemistry 9701/34 — October/November 2020

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 · Analysis, Conclusions and Evaluation · Presentation of Data and Observations · Qualitative Analysis

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

Many hydrated salts lose water of crystallisation when heated.
You will identify the metal in a hydrated salt by heating the salt until it becomes anhydrous.

The equation for the dehydration of the hydrated salt, X⋅16H2O\text{X}\cdot16\text{H}_2\text{O}, is shown.

X⋅16H2O(s)→X(s)+16H2O(g)\text{X}\cdot16\text{H}_2\text{O(s)} \rightarrow \text{X(s)} + 16\text{H}_2\text{O(g)}

FB 1 is the hydrated salt, X⋅16H2O\text{X}\cdot16\text{H}_2\text{O}.

(a)

Method

  • Weigh a crucible with its lid and record the mass.
  • Add between 1.8 g1.8\text{ g} and 2.0 g2.0\text{ g} of FB 1 to the crucible.
  • Weigh the crucible and lid with FB 1 and record the mass.
  • Place the crucible on the pipe-clay triangle. Gently heat the crucible and contents for approximately two minutes with the lid on.
  • Remove the lid. Then heat the crucible and contents strongly for approximately four minutes.
  • Replace the lid and leave the crucible and residue to cool for at least five minutes.

While the crucible is cooling, you may wish to begin work on Question 2 or 3.

  • Reweigh the crucible and contents with the lid on. Record the mass.
  • Remove the lid. Heat the crucible and contents strongly for a further two minutes.
  • Replace the lid and leave the crucible and residue to cool for at least five minutes. Then reweigh the crucible and contents with the lid on. Record the mass.
  • Calculate and record the mass of FB 1 added to the crucible and the mass of residue obtained.
5M
(b)

Calculations

(i)

Calculate the number of moles of water of crystallisation lost during heating of FB 1.

moles of H2O lost=.............................. mol\text{moles of H}_2\text{O lost} = ..............................\text{ mol}
1M
(ii)

Use your answer to (b)(i) to calculate the number of moles of anhydrous residue, X\text{X}, produced by the heating in (a).

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

Calculate the relative formula mass of X\text{X}.

Mr of X=..............................M_r\text{ of X} = ..............................
1M
(iv)

X\text{X} is the sulfate of a metal in Group 13 of the Periodic Table.

Calculate the relative atomic mass of the metal.
Show your working.

Ar of the metal=..............................A_r\text{ of the metal} = ..............................
1M
(v)

Use your answer to (b)(iv) to identify the metal present in X\text{X}.

The metal is ...............................\text{The metal is } .............................. .
1M
(c)
(i)

Suggest why the crucible and contents were heated with the crucible lid on for the first two minutes of the experiment.

1M
(ii)

Suggest whether the experiment would be more accurate if you reheated the crucible and contents strongly for a third time.
Explain your answer.

1M

The rest of this paper

2 more questions
  • Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation15M
  • Q3Qualitative Analysis · Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation13M
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