Chemistry 9701/32 — May/June 2018

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

questions

marks

120

minutes

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

Q1Presentation of Data and ObservationsManipulation, Measurement and ObservationAnalysis, Conclusions and EvaluationFree sample

Many metal hydroxides decompose when heated to produce water vapour and the metal oxide as residue.

In this experiment, you will heat a metal hydroxide $\text{M(OH)}_2$ . You will then identify the metal $\text{M}$ .

\text{M(OH)}_2(\text{s}) \rightarrow \text{MO}(\text{s}) + \text{H}_2\text{O}(\text{g})

FB 1 is the hydroxide of a metal in Group 2 of the Periodic Table, $\text{M(OH)}_2$ .
You are supplied with approximately $2\text{ g}$ of FB 1.

(a)

Method

Experiment 1

Weigh a crucible with its lid and record the mass.
Add between $0.5$ and $0.7\text{ g}$ of FB 1 to the crucible. Weigh the crucible with FB 1 and lid and record the mass.
Place the crucible on the pipe-clay triangle and remove the lid.
Heat the crucible and contents strongly for about four minutes.
Replace the lid and leave the crucible and residue to cool.
While the crucible is cooling, begin work on a different question.
Once the crucible is cool, reweigh the crucible and contents with the lid on. Record the mass.
Calculate and record the mass of FB 1 used and the mass of residue obtained.

Experiment 2

Repeat the method used in Experiment 1, using between $0.8$ and $1.0\text{ g}$ of FB 1 in the second crucible.
Calculate and record the mass of FB 1 used and the mass of residue obtained.

Results

(b)

Calculations

(i)

Calculate the mean mass of FB 1 used in your experiments and calculate the mean mass of residue obtained.

Express both answers to two decimal places.

(ii)

Calculate the mean number of moles of water lost during your experiments.

(iii)

Using your answer to (ii) and the equation for the decomposition of $\text{M(OH)}_2$ , calculate the relative formula mass of the metal oxide, $\text{MO}$ .

(iv)

Calculate the relative atomic mass of $\text{M}$ .

$\text{M}$ is in Group 2 of the Periodic Table. Suggest the identity of $\text{M}$ .

(c)

(i)

State how you could ensure that the decomposition of $\text{M(OH)}_2$ in your experiments was complete.

(ii)

A student repeated the experiment using FB 1 contaminated with $\text{MCO}_3$ .

State and explain what effect this impurity would have on the value of the relative atomic mass of $\text{M}$ that this student would calculate.

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2 more questions

Q2Presentation of Data and Observations · Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation15M
Q3Qualitative Analysis · Presentation of Data and Observations13M

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