Activity 2.5 Class 10 Science

This activity has been taken form the chapter 2 Acids, Bases and salts class 10 science of NCERT science book.

How do Metal Carbonates and Metal Hydrogen carbonates React with Acids

Aim of the activity

To observe the reaction of metal carbonates and metal hydrogen carbonates with acids and test for the evolving gas.

Materials used in the activity

1. Test tubes

2. 0.5 g sodium carbonate and 05 g sodium hydrogen carbonate

3. Dilute Hydrochloric acid (HCl)

4. Lime water solution (Calcium hydroxide)

Procedure

We will take two tests tubes, label them as A and B and take about 0.5 g of sodium carbonate (Na₂CO₃) in test A and about 0.5 g of sodium hydrogen carbonate (NaHCO₃) in test tube B.

Now we add about 2 ml of dilute HCI to both the test tubes.

After some time , we pass the gas produced in each case through lime water (calcium hydroxide solution).

Reaction of metal carbonates and metal hydrogen carbonates with acids

Observation

In the test tube A

The reaction is vigorous. A brisk effervescence can be seen in the test tube and bubbles are produced that indicate the evolution of a gas.

In the test tube B

The reaction is less vigorous but effervescence can also be seen.

On passing the gas produced in each case through lime water with the help of delivery tube. Lime water turns milky.

When the gas is passed in excess, calcium hydrogen carbonate is formed and turns milkyness.

CaCO₃(s) + CO₂(g) → H₂O(I) → Ca(HCO₃)₂(aq)

Explanation

In the test tube A

Sodium carbonate reacts with dilute hydrochloric acid to produce carbon di oxide, water and sodium chloride.

`Na_2CO_3 + 2HCl →2NaCl+ H_2O +CO_2`

In test tube B

Sodium hydrogen carbonate reacts with dilute hydrochloric acid to form carbon dioxide, water, and sodium chloride

`NaHCO_3 +HCl →NaCl+ H_2O +CO_2`

We can see the products formed in the both reactions are similar but the speed of the reaction in the both test tube is different.

The reaction is more vigorous in the test tube A than in the test tube B

Sodium carbonate is more reactive than sodium hydrogen carbonate.

Test for the evolving gas

When the gas produced in the both reactions , is passed in lime water, the lime water turns milky. An insoluble substane calcium carbonate is formed.

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(I)

Lime water milky

This indicates the gas produced is carbon dioxide.

When excess `CO_2` is passed in lime water, calcium hydrogen carbonate is formed which is soluble in water.

Conclusion

All acids decompose metal carbonates and metal hydrogen carbonates with the liberation of `CO_2` gas, water and corresponding salt.

Frequently Asked Questions

1. Why does lime water turn milky when carbon di oxide gas is passed through it?

When `CO_2` is passed through lime water `(Ca(OH)_2)`, an insoluble salt calcium carbonate is formed so lime water turns milky.

2. What happen if excess `CO_2` is passed through lime water?

When excess `CO_2` is passed through this solution, calcium carbonate reacts with more CO2 to form soluble calcium hydrogen carbonate.

CaCO3+ CO2 +H2O →Ca(HCO3)2

3. Can we use other acids in this activity2.5?

Yes, we can use other acids like sulphuric acids,nitric acids also.

4. What is the difference between the reactions of `Na2CO_3` and `NaHCO_3` with `HCl`?

In both reactions, `HCl` reacts with both salts produces `CO_2` but two moles of `HCl` are required with sodium carbonate and only one mole of `HCl` is required with sodium hydrogen carbonate.

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