Question

Temporary hardness of water is mainly caused by the presence of

• A. Bicarbonates of Ca\(^{2+}\) and Mg\(^{2+}\)
• B. Sulphates and chlorides of Ca\(^{2+}\) and Mg\(^{2+}\)
• C. Sodium salts
• D. Dissolved oxygen

Hint:

Types of hardness: \[ \boxed{ \begin{aligned} \text{Temporary hardness} &\rightarrow \text{Ca(HCO}_3)_2,\ \text{Mg(HCO}_3)_2\\ \text{Permanent hardness} &\rightarrow \text{CaSO}_4,\ \text{MgSO}_4,\ \text{CaCl}_2,\ \text{MgCl}_2 \end{aligned} } \]

Answer 1

The Correct Option is A

Step 1: Recall the two types of hardness.
Water hardness is split into temporary (carbonate) hardness and permanent (non-carbonate) hardness.
Step 2: Identify the source of temporary hardness.
Temporary hardness comes from the bicarbonates of calcium and magnesium dissolved in the water.
Step 3: Confirm with the boiling test.
Boiling breaks these bicarbonates down into insoluble carbonates that precipitate out, which is exactly why this hardness is called temporary and removable by boiling.
\[ \boxed{\text{Bicarbonates of Ca}^{2+}\text{ and Mg}^{2+}} \]