Question

What is observed when dilute sulphuric acid is mixed with solid sodium carbonate?

Answer 1

Hint: Solid sodium carbonate is a carbonate of an alkali metal. It’s a basic salt as it is formed from the neutralization reaction between carbonic acid (a weak acid) and sodium hydroxide (a weak base). Therefore the reaction between sulphuric acid and sodium carbonate would be an acid-base reaction.

Complete answer:
Dilute sulphuric acid is a diprotic acid that dissociates in an aqueous solution to give two moles of protons (hydrogen ions) and one mole of sulphate anions per mole of sulphuric acid.
Solid sodium bicarbonate is a mildly basic salt which dissociates in an aqueous solution to give two moles of sodium cations and one mole of carbonate anions per mole of the salt.
An acid-base type reaction happens between dilute sulphuric acid and sodium carbonate upon mixing. The sulphate ions from sulphuric acid combine with the sodium ions from sodium carbonate resulting in the formation of sodium sulphate salt. The released protons are utilized in making water and the leftover unreacted carbonate ions transform into carbon dioxide gas.
Thus dilute sulphuric acid reacts with sodium carbonate to give sodium sulphate salt along with water and carbon dioxide is liberated as a side product.
Brisk effervescence is observed as a consequence of carbon dioxide liberation, which also acts as an indicator for the reaction making it visible to the naked eye.
The reaction can be written as follows:
\[N{a_2}C{O_3}(s) + dil.{H_2}SO(aq) \to N{a_2}S{O_4}(aq) + {H_2}O(l) + C{O_2}(g) \uparrow \]

Note:
Apart from observing brisk effervescence, the liberation of carbon dioxide gas can also be tested by allowing the gas to pass through a solution of lime (lime water). The clear solution of lime water turns milky upon addition of carbon dioxide as a precipitate of calcium carbonate is formed in the reaction medium.