Chemistry 9701/33 — February/March 2019

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

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

Several ores of copper contain both copper(II) carbonate and copper(II) hydroxide. This combination is called basic copper(II) carbonate. You will determine the composition of an ore of copper by reacting it with an excess of acid and collecting the gas evolved.

\text{CuCO}_3(\text{s}) + \text{H}_2\text{SO}_4(\text{aq}) \rightarrow \text{CuSO}_4(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{CO}_2(\text{g})

FA 1 is a sample of basic copper(II) carbonate.
FA 2 is dilute sulfuric acid, $\text{H}_2\text{SO}_4$ .

The formula of basic copper(II) carbonate, FA 1, can be written as $x\text{CuCO}_3 \cdot y\text{Cu(OH)}_2$ .
You will use your results to determine the ratio $x:y$ in the formula.

(a)

Method

Fill the tub with water to a depth of about $5\text{ cm}$ .
Fill the $250\text{ cm}^3$ measuring cylinder completely with water. Hold a piece of paper towel firmly over the top, invert the measuring cylinder and place it in the water in the tub.
Remove the paper towel and clamp the inverted measuring cylinder so the open end is in the water just above the base of the tub.
Use the $50\text{ cm}^3$ measuring cylinder to transfer $50\text{ cm}^3$ of FA 2 into the conical flask.
Fit the bung tightly in the neck of the flask, clamp the flask and place the end of the delivery tube into the inverted $250\text{ cm}^3$ measuring cylinder.
Weigh the container with FA 1 and record the mass.
Remove the bung from the neck of the flask. Tip FA 1 into the flask and replace the bung immediately. Remove the flask from the clamp and swirl it to mix the contents. Swirl the flask occasionally until no more gas is produced.
Replace the flask in the clamp.
Reweigh the container with any residual solid and record the mass.
Calculate and record the mass of FA 1 added to the flask.
Measure and record the final volume of gas in the $250\text{ cm}^3$ measuring cylinder.

Results

(b)

Calculations

(i)

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

(ii)

Calculate the number of moles of carbon dioxide collected in the measuring cylinder.
[Assume 1 mole of gas occupies $24.0\text{ dm}^3$ under these conditions.]

\text{moles of CO}_2 = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ mol}

Hence deduce the number of moles of copper(II) carbonate in FA 1.

\text{moles of CuCO}_3 = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ mol}

(iii)

Calculate the mass of copper(II) carbonate in FA 1.

\text{mass of CuCO}_3 = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ g}

(iv)

Use your answer to (iii) and the mass of FA 1 added to the flask in (a) to calculate the mass of copper(II) hydroxide in FA 1.

\text{mass of Cu(OH)}_2 = \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\dots\text{ g}

(v)

Hence calculate the mole ratio of the two components of basic copper(II) carbonate, FA 1. This is the ratio $x:y$ .

\text{CuCO}_3 : \text{Cu(OH)}_2 = 1 : \dots\dots\dots\dots\dots\dots\dots\dots\dots\dots

x : y

(c)

How would the value of y calculated in (b) change if the experiment was carried out at a much lower temperature?

Tick ( $\checkmark$ ) the correct box. Explain your answer.


y would decrease
y would increase
y would not change

explanation:

(d)

Not all the carbon dioxide produced in the reaction is collected in the $250\text{ cm}^3$ measuring cylinder. One reason for this is that some carbon dioxide is lost before the bung can be replaced in the flask.

Give one other reason why it is not possible to collect all of the carbon dioxide produced in (a). Suggest an improvement to the method to address this.

reason:

improvement:

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2 more questions

Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Qualitative Analysis15M
Q3Manipulation, Measurement and Observation · Qualitative Analysis · Analysis, Conclusions and Evaluation15M

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