Lead Detection Using Sulphuric Acid

The question asks about the observation when six drops of sulfuric acid are added to a glass of water containing lead. This is a chemical test used to detect the presence of lead ions in a solution.

Sulphuric Acid Test for Lead

When sulfuric acid ($\text{H}_2\text{SO}_4$) is added to water containing lead ions ($\text{Pb}^{2+}$), a chemical reaction occurs. Sulphuric acid dissociates to produce hydrogen ions ($\text{H}^{+}$) and sulfate ions ($\text{SO}_4^{2-}$).

The lead ions present in the water react with the sulfate ions from the sulfuric acid to form lead sulfate ($\text{PbSO}_4$). The chemical equation for this reaction is:

$$ \text{Pb}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{PbSO}_4\text{(s)} $$

Lead sulfate ($\text{PbSO}_4$) is a compound that is generally insoluble in water. Because it is insoluble, it separates from the solution as a solid, which is called a precipitate.

Nature of the Precipitate

Lead sulfate ($\text{PbSO}_4$) is a white solid. Therefore, when it precipitates out of the solution, it appears as a white solid suspended in the water. This suspension of fine solid particles makes the water cloudy or opaque, which is observed as a white precipitate.

Why Other Options Are Incorrect

• Brown precipitate: A brown precipitate in chemical tests often indicates the presence of compounds like iron(III) hydroxide or manganese dioxide, depending on the reagents used.
• Red precipitate: A red precipitate could be formed by substances like copper(I) oxide or mercury(II) iodide under specific reaction conditions, but not typically lead with sulfuric acid.
• Yellow precipitate: A yellow precipitate might suggest the presence of lead iodide ($\text{PbI}_2$), but this is formed by reacting lead ions with iodide ions ($\text{I}^{-}$), not sulfate ions from sulfuric acid.

Thus, the reaction between lead ions and sulfuric acid specifically produces white lead sulfate.

Therefore, the presence of lead detected by adding sulfuric acid to water will yield a white precipitate.