Chemistry 9701/36 — October/November 2023

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

questions

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

When hydrogen peroxide is decomposed by a suitable catalyst, oxygen and water are produced. You will determine the concentration of a solution of hydrogen peroxide by decomposing it and measuring the mass of oxygen produced.

FB 1 is aqueous hydrogen peroxide, $\text{H}_2\text{O}_2$ .
FB 2 is the catalyst, manganese(IV) oxide, $\text{MnO}_2$ .

(a)

Method

Use the measuring cylinder to transfer $25.0\text{ cm}^3$ of FB 1 into a conical flask.
Weigh the conical flask containing FB 1. Record the mass.
Weigh the container with FB 2. Record the mass.
Tip all the FB 2 into the conical flask. Swirl the flask gently.
Weigh the container with any residual FB 2. Record the mass.
Calculate the mass of FB 2 added. Record the mass.
Leave the conical flask and its contents to stand for 30 minutes. Swirl the flask occasionally.

While the reaction is taking place, begin work on Question 2 or Question 3.

When the reaction is complete, weigh the flask and its contents. Record the mass.

You will use FB 1 in Questions 2 and 3.

(b)

Calculations

(i)

Calculate the mass of oxygen liberated.

mass of oxygen = .............................. g

(ii)

Give the equation for the decomposition of hydrogen peroxide in (a). Include state symbols.

(iii)

Calculate the concentration, in $\text{mol dm}^{-3}$ , of hydrogen peroxide in FB 1.

concentration of $\text{H}_2\text{O}_2$ in FB 1 = .............................. $\text{mol dm}^{-3}$

(iv)

The "volume strength" of hydrogen peroxide is equal to the volume of oxygen, in $\text{dm}^3$ , produced at room conditions, when $1.00\text{ dm}^3$ of a solution of hydrogen peroxide is completely catalytically decomposed.

Use your answer in (b)(iii) to calculate the volume, in $\text{dm}^3$ , of oxygen produced when $1.00\text{ dm}^3$ of FB 1 decomposes at room conditions. Your answer to this calculation is numerically equal to the "volume strength", in vol, of solution FB 1. Show your working.

"volume strength" of $\text{H}_2\text{O}_2$ in FB 1 = .............................. vol

(c)

(i)

Describe the observation to determine whether or not the decomposition of hydrogen peroxide in FB 1 is complete.

Explain your answer.

(ii)

A student suggests that the experiment in (a) would be more accurate if a loose-fitting plug of cotton wool was pushed gently into the mouth of the conical flask during the reaction.

State whether the student is correct. Explain your answer.

(iii)

Deduce the mass of manganese(IV) oxide, FB 2, left in the conical flask at the end of the experiment. Explain your answer.

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2 more questions

Q2Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation14M
Q3Manipulation, Measurement and Observation · Qualitative Analysis · Analysis, Conclusions and Evaluation · Presentation of Data and Observations14M

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