Chemistry 9701/35 — October/November 2021

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 ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

You will investigate a compound of a Group 1 element to determine which element is present. Group 1 carbonates decompose to give carbon dioxide when heated to high temperatures.

\text{X}_2\text{CO}_3(\text{s}) \rightarrow \text{X}_2\text{O}(\text{s}) + \text{CO}_2(\text{g})

FA 1 is the carbonate of the element, $\text{X}_2\text{CO}_3$ .

(a)

Method

Weigh a crucible with its lid and record the mass.
Add 1.40–1.60 g of FA 1 to the crucible.
Weigh the crucible and its lid with FA 1 and record the mass.
Place the crucible on the pipe-clay triangle. Heat the crucible, with its lid on, gently for approximately 1 minute. Then heat strongly for another minute.
Carefully remove the lid. Heat the crucible strongly for 4 minutes.
Replace the lid and leave the crucible and residue to cool for at least 5 minutes.

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

Reweigh the crucible and contents with its lid. Record the mass.
Remove the lid. Heat the crucible and contents strongly for a further 2 minutes.
Replace the lid and leave the crucible and residue to cool for at least 5 minutes. Reweigh the crucible and residue with its lid. Record the mass.
Calculate and record the mass of FA 1 added to the crucible. Calculate the mass of residue obtained.

Results

(b)

Calculations

(i)

Calculate the mass of carbon dioxide produced when the sample of $\text{X}_2\text{CO}_3$ was heated.

mass of $\text{CO}_2$ produced = .............................. g

(ii)

Calculate the number of moles of $\text{X}_2\text{CO}_3$ needed to produce the mass of carbon dioxide calculated in (b)(i).

moles of $\text{X}_2\text{CO}_3$ needed = .............................. mol

(iii)

Use your answer to (b)(ii) and the information on page 2 to calculate the relative formula mass, $M_r$ , of $\text{X}_2\text{CO}_3$ .

$M_r$ of $\text{X}_2\text{CO}_3$ = ..............................

(iv)

Use your answer to (b)(iii) to calculate the relative atomic mass, $A_r$ , of $\text{X}$ . Hence identify $\text{X}$ . Explain how you reached your conclusion.

$\text{X}$ is .............................. .

(c)

In this experiment you heated the sample of $\text{X}_2\text{CO}_3$ for approximately 8 minutes.

Explain, using evidence from your results in (a), whether your sample of $\text{X}_2\text{CO}_3$ had decomposed completely.

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2 more questions

Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation15M
Q3Manipulation, Measurement and Observation · Analysis, Conclusions and Evaluation · Qualitative Analysis14M

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