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Study Hack Lab

RP 1Chemistry

Making salts

Write-up template

Name
Date
Course
GCSE Chemistry
Board and specification
AQA GCSE Chemistry (8462), 4.4.2.3AQA GCSE Combined Science: Trilogy (8464), 5.4.2.3Apparatus and techniques: AT 2, AT 3, AT 4, AT 6
Class and teacher

Aim

Make a pure, dry sample of copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid, and work out your percentage yield.

Contents

  1. Plan and risk assessment
  2. Apparatus
  3. Method
  4. Results
  5. Graph
  6. Analysis
  7. Conclusion and evaluation
  8. Make safe and clear up

A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.

1 Plan and risk assessment

A metal oxide is a base: it neutralises an acid to make a salt and water. Copper(II) oxide is insoluble, so you add it until some is left over (in excess), filter that off, and crystallise the blue copper(II) sulfate from the solution.

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

Variables

Independent (you change)
Dependent (you measure)
Control (you keep the same)

Prediction

What colour will the solution be once the black copper(II) oxide has reacted with the acid?

Which reactant should be in excess at the end, and why?

Will you get all the crystals the acid could make (a 100 % yield)?

Risk assessment

HazardHarm it could causeControl

2 Apparatus

  • Safety goggles Protect your eyes from hot acid.
  • Dilute sulfuric acid, 1.0 mol/dm³ (irritant) The acid: 40 cm³ makes the salt.
  • 50 cm³ measuring cylinder (resolution 1 cm³) Measures 40 cm³ of acid.
  • 100 cm³ beaker and glass rod The reaction happens here; stir with the rod.
  • Bunsen burner, tripod, gauze and heatproof mat Warms the acid (and could heat the basin).
  • Copper(II) oxide powder (harmful), spatula and weighing boat The insoluble base, added until in excess.
  • Top-pan balance (resolution 0.01 g) Weighs the copper(II) oxide and the crystals.
  • Filter funnel, filter paper, clamp stand and conical flask Removes the excess copper(II) oxide.
  • Evaporating basin on a water bath (250 cm³ beaker) Evaporates water gently to the crystallisation point.
  • Crystallising dish The crystals grow here as the solution cools.
  • Watch glass and filter paper Dry and weigh the crystals.

3 Method

Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.

4 Results

The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.

The acid · Label on the bottle: 1.0 mol/dm³ sulfuric acid.

ReagentVolume of sulfuric acid in cm³
Dilute sulfuric acid

The copper(II) oxide

WeighingMass of copper(II) oxide in g
Weighed out
Left on the boat
Added to the acid

Observations

StageObservation
Adding copper(II) oxide
Filtering
Crystallising

Weighing the crystals · Weigh twice: if the two masses agree, the crystals are dry.

WeighingMass of watch glass in gMass of watch glass and crystals in gMass of crystals in g
First
Check
Dry mass used

Yield

Maximum theoretical mass of crystals in gPercentage yield in %

Anomalies

Ring any anomalous result. Say what probably went wrong and whether you repeated it.

5 Graph

This practical has no graph: summarise your results in a sentence.

6 Analysis

  1. Moles of acid (Higher)

    moles = concentration (mol/dm³) × volume (dm³)

    Answer

  2. Copper(II) oxide that reacts

    mass = moles × Mr

    Answer

  3. Copper(II) oxide you added

    mass added = mass weighed out − mass left on the boat

    Answer

  4. Maximum mass of crystals

    mass = moles × Mr

    Answer

  5. Mass of crystals

    mass of crystals = mass of watch glass and crystals − mass of watch glass

    Answer

  6. Percentage yield (Chemistry only)

    percentage yield = mass of product made ÷ maximum theoretical mass × 100

    Answer

7 Conclusion and evaluation

Conclusion

Conclusion: what do your results show? Use your own numbers.

Sources of error

For each, say whether it is systematic or random, and how it affected your results.

Copper(II) sulfate left dissolved in the solution in the dish

Solution left in the filter paper and on the beaker and basin

Crystals still wet when weighed

Acid left unreacted (cold acid, or stopping before solid stayed)

The mixture frothing over the top of the beaker

Black copper(II) oxide getting through the filter

Heating the solution to dryness

How much water was evaporated (“about half”) and how warm the room was

Improvement

How could you improve the method? Say why it would help.

8 Make safe and clear up

  • Turn off the Bunsen burner and the gas tap
  • Leave the tripod, gauze and basin to cool on the mat before you move them
  • Put the filter paper with the black copper(II) oxide in the solid waste bin
  • Hand your crystals in for recycling: not down the sink, and not home
  • Wash the glassware, wipe the bench and wash your hands