Making Salts Virtual Lab: Copper Sulfate Crystals

Updated 2026-10-07

This making salts virtual lab matches the AQA GCSE Chemistry required practical on preparing a pure, dry sample of a soluble salt from an insoluble base. Students warm dilute sulfuric acid, add copper(II) oxide one spatula at a time until some is left over, and filter off the excess. They heat the filtrate to the point of crystallization, cool it and weigh blue copper sulfate crystals. Then they calculate the percentage yield and see what goes wrong if the solution is evaporated to dryness.

Making a salt – copper sulfate crystals from an insoluble base and acid

Curriculum links

AQA GCSE Chemistry 4.4.2.3 (soluble salts) and its required practical on making a pure, dry sample of a soluble salt from an insoluble oxide or carbonate. In Combined Science: Trilogy the same content is 5.4.2.3.
AQA GCSE Chemistry 4.3.3.1 (percentage yield), for questions 3–5.
AP Chemistry Unit 4, topic 4.5 Stoichiometry: the theoretical yield comes from the moles of the limiting reactant.
NGSS HS-PS1-7: use mathematical representations to support conservation of mass in a reaction.

Simulic is not affiliated with or endorsed by the College Board or AQA.

Before the lab (5 min)

Ask students to commit to a prediction, on paper or as question 1 of the class link:

"You make copper sulfate twice. The first time you stop heating when crystals form on a cold glass rod and let the solution cool. The second time you boil off all the water. What do you get the second time?"

Many students say "more crystals, because none is left in the water". Don't correct them yet.

Method in the simulation

Set Acid to dilute H₂SO₄, Base to CuO, Volume to 25 cm³, Concentration to 1.0 mol/dm³, Evaporate to "until crystals form" and Cooling to "slow, at room temperature".
Press 1. Warm the acid. Add the base with + 1 spatula CuO, one at a time, until the info box says some base no longer dissolves. Record the number of spatulas.
Press 3. Filter off excess base, then 4. Heat to crystallisation point. Watch the glass rod: heating stops when crystals form on it.
Press 5. Leave to cool and crystallise, then 6. Collect, dry and weigh. Record the mass, the theoretical mass and the yield from the results table.
Press New run. Change Cooling to the ice bath and repeat. Then set Cooling back to slow, set Evaporate to "to dryness" and repeat.

Run	Evaporate	Cooling
1	until crystals form	slow
2	until crystals form	ice bath
3	to dryness	slow

Auto run does every step. Have students press the buttons themselves on the first run so they learn the order.

the watch glass of blue crystals with the balance reading 4.67 g and the yield calculation below

Expected results

Readings from the simulation with the settings above:

Run	Product	Mass (g)	Theoretical (g)	Yield	Crystal size
Slow cooling	blue CuSO₄·5H₂O crystals	4.67	6.24	74.8%	5.9 mm
Ice bath	blue CuSO₄·5H₂O crystals	4.38	6.24	70.2%	1.9 mm
To dryness	white anhydrous CuSO₄ powder	3.29	6.24	52.7%	powder

Four spatulas (2.4 g) of CuO are needed. The fourth leaves 0.41 g undissolved, which shows all 0.0250 mol of acid has reacted.
The theoretical mass is 0.0250 mol × 249.7 g/mol = 6.24 g, because H₂SO₄ is the limiting reactant.
The 1.57 g lost in the slow run splits into 1.29 g still dissolved in the leftover solution, 0.19 g soaked into the filter paper and 0.10 g lost while drying.
Slow cooling grows a few large crystals; the ice bath makes many small ones.
CuCO₃ gives the same masses as CuO, but fizzes while it reacts.

Questions for students

(Prediction, asked again after the lab) What do you get if you evaporate the copper sulfate solution to dryness?
When you compare slow cooling with an ice bath, which variables must stay the same?
With the standard settings and slow cooling, what mass of crystals do you weigh?
Calculate the percentage yield.
Where did most of the missing copper sulfate go, and how could you recover more?

Answers for teachers: (1) Less product: 3.29 g of white anhydrous powder instead of 4.67 g of blue crystals. (2) The acid, the base, the acid volume and concentration, and how far the solution is evaporated. (3) 4.67 g (accept 4.62–4.72). (4) 4.67 ÷ 6.24 × 100 = 74.8% (accept 73.8–75.8). (5) Most of it (1.29 g) stays dissolved in the leftover solution, because copper sulfate is still soluble at room temperature. Evaporate that solution again for a second crop of crystals.

Common misconceptions

"Excess base contaminates the salt." It is insoluble, so filtering removes it. Excess makes sure no acid is left in the product.
"Boiling off all the water gives the most crystals." The blue crystals contain water. Heating to dryness destroys them.
"The yield should be 100% if I am careful." Some salt always stays dissolved in the cold solution that is poured off.
"An ice bath makes more crystals, so it is better." It makes smaller crystals. In this simulation the yield is also lower, because slow cooling over a day or two lets a little more water evaporate.

Extension

Scale up: set 50 cm³ of 1.0 mol/dm³ acid. Ask students to predict the mass before running it. It doubles to 9.34 g, but the yield stays 74.8%.
A different salt: switch to dilute HCl. CuCl₂ is far more soluble than CuSO₄, so more of it stays in the leftover solution: 1.14 g of CuCl₂·2H₂O crystals, a 53.5% yield. Ask why very soluble salts are harder to crystallize.

FAQ

Can students do the whole required practical without a lab?

They can follow every step, see why each one matters and calculate the yield. Use the simulation to teach the method before the wet lab, or instead of it when time is short. Students still need to handle real apparatus at some point.

Why does the simulation use cm³ and mol/dm³?

These are the units in the AQA specification. 1 cm³ is 1 mL and 1 mol/dm³ is 1 M, so US classes can read them directly.

How do I give each class a different setup?

Change the starting values on the class link, for example 40 cm³ of 1.5 mol/dm³ acid. Run it once yourself and rewrite the numbers in questions 3 and 4 before class.