Chemistry: Turning a Metal Carbonate into a Salt (and Why the Lab Gets Fizzy!)

 

Chemistry: Turning a Metal Carbonate into a Salt (and Why the Lab Gets Fizzy!)

If you drop a metal carbonate into an acid in the laboratory, something rather satisfying happens — it fizzes vigorously. That fizzing is carbon dioxide gas being produced as the carbonate reacts with the acid to form a salt, water, and carbon dioxide.

This reaction is one of the most common practical experiments in GCSE and A-Level chemistry, and it neatly demonstrates how acids react with carbonates.

The General Reaction

When a metal carbonate reacts with an acid, the products are always:

• A salt

• Water

• Carbon dioxide gas

Metal carbonate + Acid → Salt + CO₂ + Water

The bubbles you see during the reaction are CO₂ escaping from the solution.

A common school experiment uses calcium carbonate (marble chips) and hydrochloric acid.

The reaction is:

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

Here:

• Calcium carbonate reacts with hydrochloric acid

• The salt produced is calcium chloride

• Carbon dioxide gas bubbles off

• Water remains in solution

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How Students Identify the Gas

One of the nicest parts of this experiment is testing the gas produced.

Carbon dioxide is confirmed by bubbling the gas through limewater.

If the gas is CO₂:

• Limewater turns milky white

• This happens because calcium carbonate precipitates.

This test is often used in both GCSE required practicals and introductory A-Level work.

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Making Different Salts from Carbonates

Different acids produce different salts.

Acid Used	Salt Produced	Example Reaction
Hydrochloric acid	Chloride salt	CaCl₂
Sulfuric acid	Sulfate salt	CuSO₄
Nitric acid	Nitrate salt	Zn(NO₃)₂

For example:

Copper carbonate + sulfuric acid → copper sulfate + CO₂ + water

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Why Teachers Love This Reaction

This simple reaction demonstrates several key chemistry ideas:

• Acid–base chemistry

• Gas evolution reactions

• Identification of carbon dioxide

• Salt preparation techniques

It is also visually satisfying — the fizzing makes it very clear that a chemical reaction is happening.

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Tip for students:
If you ever see a question in an exam involving carbonates and acids, remember the rule:

Carbonates always produce carbon dioxide.