Launch practical
About 120 minutes
- Set up the bench with the 11 items of apparatus.
- Take the readings yourself, into the results table you draw first.
- Process your results.
- Answer exam questions on your own results, which you mark against the mark scheme.
Runs in your browser: a 3D bench with 2D close-ups of each instrument for exact readings. Nothing to install and no account.
What you measure, and how
One run takes 9 readings. You take every one yourself, the way you would in class.
- On the 3D bench (Fig. 1) you set out the apparatus and read each instrument where it stands.
- In the 2D close-up (Fig. 2) the same instrument is drawn large, from the same run, for an exact reading. It is also how the practical runs on a device that cannot show 3D.
- In your table you write what you read, to the instrument’s resolution, and the notebook checks it against the instrument.
How to read it. The 50 cm³ cylinder. Each small division is 1 cm³. Read the bottom of the meniscus, with your eye level with it.
What it shows
CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
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.
The graph to expect. This practical has no graph. The result is the percentage yield, worked out from two masses.
Key equation for the exam: metal oxide + acid → salt + water.
Equation to write. Name the salt from the acid: sulfuric gives a sulfate, hydrochloric a chloride.
Apparatus
| Item | What it is for | Resolution |
|---|---|---|
| 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 | Measures 40 cm³ of acid. | 1 cm³ |
| 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 | Weighs the copper(II) oxide and the crystals. | 0.01 g |
| 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. | — |
Method
In our own words, as the Lab runs it. Your school's method sheet may differ in detail.
Which version are you doing?
Boards set this practical differently. Your course setting picks one; you can change it before you start.
Why: AQA makes a soluble salt as crystals. The exam questions follow your board.
Put on safety gogglesSafety
Put on goggles and keep them on until everything is cleared away. Tie back long hair.
Why: Hot acid can spit or froth into your eyes, and long hair can catch in a Bunsen flame.
Set up the heating
Stand the Bunsen burner on a heatproof mat, with the tripod and gauze over it. Put the 100 cm³ beaker on the gauze.
Why: The gauze spreads the heat so the beaker heats evenly; the mat protects the bench.
Set up the filter funnel
Fold a filter paper into a cone, put it in the funnel and clamp the funnel in the stand over the conical flask.
Why: The paper will hold back the excess copper(II) oxide while the dissolved salt passes through.
Get the water bath ready
Half fill the 250 cm³ beaker with water. The evaporating basin will sit on top of it.
Why: A water bath heats the solution gently: it cannot go above 100 °C, so the salt does not spit or break down.
Take the readings
Volume of acid; mass of copper(II) oxide before and after adding; observations at each stage; mass of the watch glass, then with the crystals (weighed twice to check they are dry).
Repeats: AQA’s method makes one batch of crystals: they take a day to grow, so there are no repeat readings. The second weighing of the crystals is a check that they are dry, not a repeat. To see whether your yield is reproducible, compare it with other groups in the class, or make a second batch.
Make safe and clear upSafety
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.
While you take readings
Warm the acid
Pour the acid into the beaker on the gauze. Heat it gently until it is almost boiling, then turn the Bunsen off.
Why: The copper(II) oxide reacts much faster with warm acid. Do not boil it: hot acid spits.
Add the copper(II) oxide
How will you add the copper(II) oxide to the acid?
Do: A small spatula at a time, stirring with the glass rod.
Why: Powder dropped into hot acid makes it froth up.
Decide when to stop adding
When will you stop adding copper(II) oxide?
Do: When some black powder stays at the bottom, however much I stir.
Why: All the acid must react, so that only copper(II) sulfate and water are left in the solution.
Filter the mixture
How will you pour the mixture into the funnel?
Do: Slowly, down the glass rod, keeping the liquid below the top of the paper.
Why: Only the solution should reach the flask: any black solid that gets through ends up in your crystals.
Concentrate the solution
Pour the filtrate into the evaporating basin. How will you heat it?
Do: On the water bath, until about half of the solution is left.
Why: You need to evaporate some of the water so the solution is concentrated enough to crystallise as it cools (the crystallisation point).
Leave it to crystallise
Pour the hot solution into the crystallising dish. How will you cool it?
Do: Leave it in a cool place for 24 hours.
Why: Less copper(II) sulfate can stay dissolved in cold water, so crystals form as the solution cools. How fast it cools decides how big they grow.
Dry the crystals
Lift the crystals out with a spatula and pat them gently between two pieces of filter paper before weighing.
Why: Solution clinging to the crystals adds to their mass and leaves impurities as it dries.
Hazards and control measures
| Hazard | What could happen | Control measure |
|---|---|---|
| Hot dilute sulfuric acid (1.0 mol/dm³, irritant) | Irritates the eyes and skin; hot acid splashing into the eyes can damage them | Wear goggles; heat the acid only until it is almost boiling, then turn the Bunsen off. |
| Hot acid frothing up when the oxide is added | Hot acid splashes onto skin or into eyes | Add the copper(II) oxide a small spatula at a time, stirring. |
| Copper(II) oxide powder (harmful) | Harmful if swallowed; the dust irritates the eyes and lungs | Use a spatula, do not raise dust, and wash your hands afterwards. |
| Copper(II) sulfate (harmful; toxic to water life) | Harmful if swallowed; irritates the eyes and skin | Hand the crystals in for recycling; never take them home or pour solutions down the sink. |
| Bunsen flame and the hot tripod, gauze and basin | Burns; hair or paper catching fire | Tie long hair back, use the yellow safety flame when not heating, and let things cool before moving them. |
| Solution heated to dryness | Hot solid spits into the eyes; the basin can crack | Heat on a water bath and stop when about half of the solution is left. |
Variables
- Independent: you change
- None: this is a preparation, not an investigation
- Dependent: you measure
- Mass of dry crystals in g
- Control: you keep the same
- Volume and concentration of the acid. 40 cm³ of 1.0 mol/dm³ sulfuric acid.
- Copper(II) oxide in excess. Keep adding until some stays after stirring.
- How far the solution is evaporated. To the crystallisation point, about half the volume.
Results from a specimen run
| Reagent | Volume of sulfuric acid in cm³ |
|---|---|
| Dilute sulfuric acid | 40 |
| Weighing | Mass of copper(II) oxide in g |
|---|---|
| Weighed out | 4.06 |
| Left on the boat | 0.37 |
| Added to the acid | 3.69 |
| Stage | Observation |
|---|---|
| Adding copper(II) oxide | The black powder disappears and the colourless acid turns blue. In the end some black powder stays at the bottom however much you stir. |
| Filtering | A clear blue solution drips into the flask. The black solid stays on the filter paper. |
| Crystallising | Large blue crystals with flat faces and sharp edges, in a little blue solution. |
| Weighing | Mass of watch glass in g | Mass of watch glass and crystals in g | Mass of crystals in g |
|---|---|---|---|
| First | 33.32 | 37.78 | 4.46 |
| Check | 33.32 | 37.77 | 4.45 |
| Dry mass used | blank | blank | 4.46 |
| Maximum theoretical mass of crystals in g | Percentage yield in % |
|---|---|
| 9.98 | 45 |
Processing the data
- Moles of acid (Higher)
- 0.040 mol
- Copper(II) oxide that reacts
- 3.18 g
- Copper(II) oxide you added
- 3.69 g
- Was it in excess?
- Yes: I added more than reacts with all the acid.
- Maximum mass of crystals
- 9.98 g
- Mass of crystals
- 4.46 g
- Percentage yield (Chemistry only)
- 45 %
| Quantity | Specimen run | Accepted |
|---|---|---|
| Percentage yield (careful technique on the same acid) | 45 % | 44 % |
| Mass of dry crystals (careful technique) | 4.46 g | 4.44 g |
Across 120 simulated careful groups, percentage yield came out between 39.7 and 67.9 % (median 54.9). That is the simulation's model, not a promise of what a real class gets.
Common mistakes and the fix
Mistakes to check in this practical, and what to do instead. In a write-up or an exam answer, the mark goes to naming the step and saying what it does to the readings.
Method: Skip them
No effect on your data, but a splash of hot acid could damage your eyes: flagged in the safety review.
The fix: Put on safety goggles. Hot acid can spit or froth into your eyes, and long hair can catch in a Bunsen flame.
Method: Use the acid cold
Copper(II) oxide reacts very slowly with cold acid. Black powder seems to stay after only a few spatulas, so you stop with 12–30 % of the acid not reacted. You get fewer crystals (roughly a third fewer) and they are wet with acid.
The fix: Warm the acid. The copper(II) oxide reacts much faster with warm acid. Do not boil it: hot acid spits.
Method: Tip it all in at once
In hot acid the mixture froths up and some spills over the top of the beaker: 5–20 % of your solution is lost, and hot acid splashes (a hazard).
The fix: Add the copper(II) oxide. Powder dropped into hot acid makes it froth up.
Volume of sulfuric acid: Typed 41 cm³
The fix: That is one division too high: read the bottom of the meniscus, not the top edge where the acid creeps up the glass.
Adding copper(II) oxide to the acid: Recorded “The black powder disappears and the colourless acid turns blue. In the end some black powder stays at the bottom however much you stir.”
The fix: Look again at the beaker: in cold acid the powder dissolves only slowly, and the solution stays a pale blue.
Exam answer: Leaving out: CuSO₄ and H₂O (correct formulae)
The fix: The products of a metal oxide and an acid are a salt and water: CuSO₄ and H₂O.
Exam answer: Leaving out: State symbols: CuSO₄(aq) and H₂O(l)
The fix: The copper(II) sulfate is dissolved in water: (aq). Water is a liquid: (l).
Worked exam-style questions
Written for Study Hack in the style of exam questions, on the specimen run above. They are not taken from any exam board's papers. Try each one before you open the worked answer.
- Question 1Equations and state symbols · Knowledge[2 marks]
A student made copper(II) sulfate from copper(II) oxide and dilute sulfuric acid.
Complete the balanced equation for the reaction. Include state symbols.
CuO(s) + H₂SO₄(aq) → ________ + ________
Worked answer and how the marks are given
A full-mark answer
CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)
Mark scheme
- CuSO₄ and H₂O (correct formulae)
- State symbols: CuSO₄(aq) and H₂O(l) Only with the mark for: CuSO₄ and H₂O (correct formulae).
Where marks are usually lost
- Missing: CuSO₄ and H₂O (correct formulae). The products of a metal oxide and an acid are a salt and water: CuSO₄ and H₂O.
- Missing: State symbols: CuSO₄(aq) and H₂O(l). The copper(II) sulfate is dissolved in water: (aq). Water is a liquid: (l).
- Question 2Moles and theoretical mass · Applying knowledge[3 marks]
You used 40 cm³ of 1.0 mol/dm³ sulfuric acid.
One mole of sulfuric acid makes one mole of copper(II) sulfate crystals, CuSO₄·5H₂O.
- Relative formula mass (Mr) of CuSO₄·5H₂O
- 249.5
GCSE Chemistry only, Higher tier.
Calculate the maximum mass of copper(II) sulfate crystals that could be made.
Maximum mass = g
Worked answer and how the marks are given
A full-mark answer
moles of acid = 1.0 × 40 ÷ 1000 = 0.04 mol
mass = 0.04 × 249.5
mass = 9.98 gMark scheme
- Moles of acid = 1.0 × 40 ÷ 1000 = 0.04 mol (method)
- Mass = moles × 249.5 (method)
- Maximum mass = 9.98 g
- Allow answers from 9.920 to 10.04 g (the marker's tolerance; correct rounding of the student's own working is also accepted).
- Allow the unit written as grams, gram, gs.
- A correct answer with no working scores full marks.
Where marks are usually lost
- Answer 9980 g (gains 1 mark). The volume must be in dm³: 40 cm³ = 0.04 dm³, so moles = 0.04 and the mass = 0.04 × 249.5 = 9.98 g.
- Answer 6.38 g (gains 1 mark). You used the Mr of anhydrous copper(II) sulfate (159.5). The crystals contain water, CuSO₄·5H₂O, so use 249.5: 0.04 × 249.5 = 9.98 g.
- Answer 3.18 g (gains 1 mark). 3.18 g is the mass of copper(II) oxide that reacts. The question asks for the crystals: 0.04 × 249.5 = 9.98 g.
- Question 3Describing the method · Knowledge[6 marks]
Magnesium sulfate is a soluble salt. It can be made from magnesium oxide, which is insoluble, and dilute sulfuric acid.
Describe a method to make pure, dry crystals of magnesium sulfate from magnesium oxide and dilute sulfuric acid.
Worked answer and how the marks are given
A full-mark answer
1. Measure about 40 cm³ of dilute sulfuric acid into a beaker.
2. Warm the acid gently with a Bunsen burner, then turn it off.
3. Add magnesium oxide a little at a time, stirring with a glass rod.
4. Keep adding until the magnesium oxide is in excess: some solid stays and does not disappear.
5. Filter the mixture with a filter funnel and filter paper to remove the excess magnesium oxide.
6. Heat the filtrate in an evaporating basin on a water bath to evaporate some of the water, until the crystallisation point.
7. Leave the solution to cool and crystallise.
8. Remove the crystals and pat them dry with filter paper.Mark scheme
Indicative content:
- Put dilute sulfuric acid in a beaker (measure a volume)
- Warm the acid
- Add magnesium oxide (a little at a time) and stir
- Until the magnesium oxide is in excess / solid remains
- Filter (with filter paper and funnel) to remove the excess magnesium oxide
- Heat the solution (in an evaporating basin, on a water bath or electric heater) to evaporate some water / to the crystallisation point
- Leave to cool and crystallise
- Pat the crystals dry with filter paper (or leave in a warm place to dry)
Levels of response Level Marks What the answer does 3 5–6 A coherent method that would give valid results: all the important steps are there, in a sensible order. 2 3–4 A method that might not give valid results: most of the important steps are there, but some are missing or out of order. 1 1–2 A method that would not give valid results: some relevant steps are given, but they are not linked into a workable method. In Study Hack a six-mark answer is not given an automatic level: you tick the points your answer makes, then choose the level that fits it.
- No relevant content: 0 marks.
Evaluate
| Source of error | Type | Effect | Improvement |
|---|---|---|---|
| Copper(II) sulfate left dissolved in the solution in the dish | Systematic | Crystals only form from the salt that cannot stay dissolved, so the mass of crystals and the yield are always lower than the theoretical maximum. | Evaporate a little more water before leaving it, or evaporate the left-over solution again for a second batch of crystals. |
| Solution left in the filter paper and on the beaker and basin | Systematic | Salt that never reaches the dish cannot crystallise, so the yield is lower. | Rinse the filter paper and the glassware with a little distilled water into the filtrate. |
| Crystals still wet when weighed | Systematic | The solution on them adds mass, so the mass of crystals and the yield come out too high (even over 100 %). | Pat the crystals dry between filter paper and reweigh until two masses agree. |
| Acid left unreacted (cold acid, or stopping before solid stayed) | Systematic | Less copper(II) sulfate is made, so the yield is lower, and the left-over acid makes the crystals impure. | Warm the acid and keep adding copper(II) oxide until some stays after stirring. |
| The mixture frothing over the top of the beaker | Systematic | Solution lost over the side takes salt with it, so the yield is lower. | Add the copper(II) oxide a small spatula at a time, stirring. |
| Black copper(II) oxide getting through the filter | Systematic | The crystals are not pure, and the black specks add a little mass. | Pour slowly down a glass rod, keep the liquid below the top of the paper, and filter again if the filtrate is not clear. |
| Heating the solution to dryness | Systematic | The salt spits out and loses its water of crystallisation, so the product is a white-blue powder, not the blue crystals, and its mass cannot be compared with the theoretical mass of crystals. | Heat on a water bath (or an electric heater) only until the crystallisation point, then leave it to crystallise. |
| How much water was evaporated (“about half”) and how warm the room was | Random | Each group evaporates a different amount and leaves its dish somewhere a little warmer or cooler, so yields spread out across the class. | Evaporate to the crystallisation point (a drop on a cold glass rod forms crystals) instead of judging “about half” by eye. |
Repeatable. When you make a second batch the same way, with the same apparatus, you get a similar mass of crystals.
Reproducible. Another group, or a different method (an electric heater instead of a water bath), gets a similar percentage yield.
Other exam boards
How this practical lines up with other GCSE boards' required or core practicals. Codes only; check your own specification for the exact activity.
| Board | Practical | Match | What is different |
|---|---|---|---|
| AQA | Required practical 1 | This page | — |
| Edexcel | 3.17 | Same activity | — |
Print it
- Blank write-up: the nine-step lab book with the correct table headings, ready to print for a real lesson.
- Specimen lab book: this page's run written up in full, with its exam answers ticked against the mark scheme.
- Printable method card: the practical on one index card. Practise with the cards in Study Hack.
- Practical workbook: a full simulated data set to process on paper, with exam questions and answers.
- Teacher and technician pack: apparatus lists, technician notes and marking points.