Test Index

BECE Science 2019 Paper

Question : 17

Total: 40

Solution:

Concept:

Water hardness is mainly caused by dissolved calcium and magnesium ions, which can be removed by precipitation using carbonate ions.

Explanation:

Sodium carbonate,

\mathrm{Na}_2\mathrm{CO}_3

, provides carbonate ions that react with calcium and magnesium ions to form insoluble precipitates.

For example,

\mathrm{Ca}^{2+} + \mathrm{CO}_3^{2-} \rightarrow \mathrm{CaCO}_3 \downarrow

This removes the hardness-causing ions from the water.

Answer:

\mathrm{Na}_2\mathrm{CO}_3

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