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Edexcel A-Level Chemistry AS Practical Skills in Chemistry I Questions

Identify the experimental aim and variables first, then connect apparatus or conditions to the chemistry, calculate from recorded data and justify improvements directionally.

Syllabus
First assessment 2019
Course
Chemistry YCH11
Level
AS

Exam points

  • Apply chemical principles to explain apparatus behaviour, feasibility and observations.
  • Control relevant variables and link each control to validity or fair comparison.
  • Process practical data and evaluate methods through uncertainty, bias and directional effects.

Covered syllabus points

3.P1—Solving practical-context problems3.P2—Controlling variables3.P3—Presenting data3.P4—Evaluating results and conclusions3.P5—Uncertainties and errors3.P6—Evaluating an experimental method3.P7—Plotting and interpreting graphs3.P8—Processing and analysing data3.P9—Significant figures3.P10—Accuracy and precision3.P11—Selecting laboratory apparatus3.P12—Using apparatus and techniques3.P13—Range and resolution of apparatus3.P14—Health and safety3.P15—Tests for ions and gases3.P16—Tests for organic functional groups3.P17—Measurements and data in Units 1 and 23.P18—Preparing inorganic and organic compounds

Question 1

[Maximum number: 9]

A group of students carried out a thermochemistry experiment to determine the relative atomic mass of a metal, M.

Procedure Step 1 Transfer 50.0 cm350.0 \mathrm{~cm}^{3} of a 1.35 moldm−31.35 \mathrm{~mol} \mathrm{dm}^{-3} solution of copper(II) sulfate to an expanded polystyrene cup placed in a glass beaker. Step 2 Weigh out, as accurately as possible, a known mass of the finely powdered metal M. Step 3 Measure the temperature of the copper(II) sulfate solution. Step 4 Quickly add all of the powdered metal, stir the mixture continuously and note the highest temperature reached.

Figure for Question 1 — Edexcel A-Level Chemistry AS

Question (a)

(a)

Each student carried out the experiment using a different mass of the metal.

[ 3 ]

Question (i)

(i)

Give a reason, other than preventing heat loss, for placing the polystyrene cup in a glass beaker.

[ 1 ]

Question (ii)

(ii)

Name the piece of apparatus suitable for measuring 50.0 cm350.0 \mathrm{~cm}^{3} of copper(II) sulfate solution.

[ 1 ]

Question (iii)

(iii)

Powdered metal reacts much faster than filings or granules. Suggest why this is important in this experiment.

[ 1 ]

Question (b)

(b)

The students' results were collected in a table.

Table for Question (b) — Edexcel A-Level Chemistry AS
[ 6 ]

Question (i)

(i)

Plot a labelled graph of mass of metal on the horizontal axis against temperature change on the vertical axis.

Table for Question (i) — Edexcel A-Level Chemistry AS
[ 3 ]

Question (ii)

(ii)

Determine the mass of metal M that reacts exactly with 50.0 cm350.0 \mathrm{~cm}^{3} of 1.35 moldm−31.35 \mathrm{~mol} \mathrm{dm}^{-3} copper(II) sulfate by drawing appropriate best-fit straight lines. You must show your working on the graph. Mass of metal M g

[ 2 ]

Question (iii)

(iii)

One mass of M in the experiment gave an anomalous data point. Suggest a reason, other than measurement error, for this anomaly.

[ 1 ]

Question 2

[Maximum number: 5]

A student carried out an experiment to identify the metal M in the hydrated carbonate M2CO3⋅10H2O\mathrm{M}_{2} \mathrm{CO}_{3} \cdot 10 \mathrm{H}_{2} \mathrm{O}. A solution was made by dissolving 3.56 g of the hydrated metal carbonate in distilled water and making the volume up to 250.0 cm3250.0 \mathrm{~cm}^{3} in a volumetric flask. 25.0 cm325.0 \mathrm{~cm}^{3} of this solution was placed in a conical flask and titrated with 0.100 moldm−30.100 \mathrm{~mol} \mathrm{dm}^{-3} of hydrochloric acid. The equation for the reaction is

M2CO3(aq)+2HCl(aq)→2MCl(aq)+H2O(l)+CO2( g)\mathrm{M}_{2} \mathrm{CO}_{3}(\mathrm{aq})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow 2 \mathrm{MCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{CO}_{2}(\mathrm{~g})

Question (a)

(a)

Name a suitable piece of apparatus to measure the 25.0 cm325.0 \mathrm{~cm}^{3} of solution.

[ 1 ]

Question (b)

(b)

The results of the titration are shown.

Table for Question (b) — Edexcel A-Level Chemistry AS
[ 1 ]

Question (i)

(i)

Complete the table.

[ 1 ]

Question (c)

(c)

The titration was repeated without using an indicator. Describe how you would obtain large, dry crystals of the metal chloride, MCl , from this titration solution. Diagrams are not required.

[ 3 ]

Question 3

[Maximum number: 5]

Precipitation reactions can be used to determine the formulae of compounds.
A bottle has a torn label which shows that it contains a nitrate with the formula X(NO_3)_2.

Figure for Question 3 — Edexcel A-Level Chemistry AS

Procedure
- a technician dissolved a sample of 12.41 g of the nitrate in deionised water to make 100 cm^3 of solution
- the technician pipetted 5.0 cm^3 of 1.50 mol dm^-3 potassium iodide into each of a series of test tubes
- each test tube then had a volume of the nitrate solution added to it as shown in the table
- a cloudy yellow solution formed, and the precipitate was allowed to settle
- the height of the precipitate was then measured.

The equation for the reaction is

X(NO3)2(aq)+2KI(aq)→XI2( s)+2KNO3(aq)\mathrm{X}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+2 \mathrm{KI}(\mathrm{aq}) \rightarrow \mathrm{XI}_{2}(\mathrm{~s})+2 \mathrm{KNO}_{3}(\mathrm{aq})

The results of the experiment are shown.

Table for Question 3 — Edexcel A-Level Chemistry AS

Question (a)

(a)

Plot the data on the grid.

Figure for Question (a) — Edexcel A-Level Chemistry AS
[ 2 ]

Question (b)

(b)

Determine the minimum volume of nitrate solution needed to react completely with 5.0 cm^3 of potassium iodide solution. You must show your working on the graph.

[ 2 ]

Question (c)

(c)

Suggest why some of the precipitate heights may be above the maximum height expected. Assume there were no measurement errors.

[ 1 ]
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