How to Prepare Copper(II) Sulfate

In this video, we work out the chemical reactions to prepare pure copper(II) sulfate salt.

When preparing any salt, the first step is to determine whether the salt is soluble or insoluble in water. Copper(II) sulfate is a soluble salt.

According to solubility rules, most sulfate salts are soluble in water, except for calcium sulfate, lead(II) sulfate, and barium sulfate. Since copper(II) sulfate is soluble, we can prepare it using the reaction between an acid and a suitable substance.

There are three common ways to prepare a soluble salt using an acid:

Acid + Reactive metal
Acid + Carbonate
Acid + Base (oxide or hydroxide)

These can be remembered using the phrase: “My Cute Baby” (Metal, Carbonate, Base).

Method 1: Acid + Reactive Metal

This method involves reacting a reactive metal with an acid. Do note, different metals react with acids at different rates. Some metals are very reactive and reaction with acids is very vigorous and fast, some metals are not so reactive, or even unreactive.
Metals like copper, silver and gold do not react with dilute acids under normal laboratory conditions. Hence, to form copper(II) sulfate in the lab, we can’t use this method because copper metal is unreactive with dilute sulfuric acid.

Note: Metals like copper, silver, and gold do not react with dilute acids. Therefore, we cannot use this method to prepare copper(II) sulfate.

Method 2: Acid + Carbonate (Recommended)

What about reaction with carbonate? Can we make use of the reaction of acid and carbonate to make copper(II) sulfate? Yes we can. To provide the sulfate ion, we will choose sulfuric acid, and the carbonate we use needs to contain the copper(II) ion. Hence, we will use copper(II) carbonate. When copper(II) carbonate reacts with sulfuric acid, copper(II) sulfate is formed, together with water and carbon dioxide gas. We can’t observe the production of water, but we will observe effervescence in this reaction due to production of carbon dioxide gas.

Chemical equation:

$\text{CuCO}_3(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{CuSO}_4(aq) + \text{H}_2\text{O}(l) + \text{CO}_2(g)$

Observations:

Effervescence is observed due to the release of carbon dioxide gas.
A blue solution of copper(II) sulfate is formed.

This is a suitable method because copper(II) carbonate is insoluble, but the resulting copper(II) sulfate is soluble.

Method 3: Acid + Base (Oxide)

What about reaction with oxide? Yes we can. Similarly, to provide the sulfate ion, we will choose sulfuric acid, and the oxide we will need to choose must contain copper(II) ion. Hence, we will use copper(II) oxide. When copper(II) oxide reacts with sulfuric acid, copper(II) sulfate is formed, together with water. In this reaction, no gas is formed. We will not observe any effervescence. Hence in order to ensure complete reaction, we will add insoluble copper(II) oxide in excess, and we can get rid of that by filtering away later. After forming copper(II) sulfate, we will be interested to obtain the solid salt from this solution. We will achieve that by crystallisation.

Chemical equation:

$\text{CuO}(s) + \text{H}_2\text{SO}_4(aq) \rightarrow \text{CuSO}_4(aq) + \text{H}_2\text{O}(l)$
Key points:

No gas is produced in this reaction.
To ensure complete reaction, excess copper(II) oxide is added.
The excess solid is then removed by filtration.
A blue solution of copper(II) sulfate is obtained.

Obtaining Solid Copper(II) Sulfate

After obtaining the copper(II) sulfate solution from either Method 2 or Method 3, we can obtain the solid salt by crystallisation.

Steps:

Heat the solution to concentrate it (evaporate some water).
Allow the solution to cool slowly.
Crystals of copper(II) sulfate will form.
Filter and dry the crystals between filter papers.

Summary of Methods

Method	Reactants	Observation	Suitable for CuSO₄?
Acid + Reactive Metal	Cu + H₂SO₄	No reaction	No
Acid + Carbonate	CuCO₃ + H₂SO₄	Effervescence (CO₂)	Yes
Acid + Base (Oxide)	CuO + H₂SO₄	No gas, blue solution	Yes