Question

Which of the following statement is false? (1) Both temporary and permanent hardness can be removed on boiling. (2) Hard water is not fit for washing clothes because it gives precipitate with soap. (3) Hardness of water is due to \(\mathrm{Mg}^{2+}\) and \(\mathrm{Ca}^{2-}\) ions. (4) Both temporary and permanent hardness of water can be removed by using washing soda.

Short answer

The false statement is: (1) Both temporary and permanent hardness can be removed on boiling.

Step-by-step solution

- Understanding Temporary and Permanent Hardness

Temporary hardness of water is due to the presence of bicarbonates of calcium and magnesium. Permanent hardness is due to the presence of chlorides and sulfates of calcium and magnesium. Temporary hardness can be removed by boiling, but permanent hardness cannot.

- Examine Statement 1

Statement 1 claims that both temporary and permanent hardness can be removed by boiling. As previously stated, boiling only removes temporary hardness. Therefore, Statement 1 is false.

- Examine Statement 2

Hard water reacts with soap to form an insoluble precipitate, making it less effective for washing clothes. Thus, Statement 2 is true.

- Examine Statement 3

Hardness of water is indeed due to the presence of \(\text{Mg}^{2+}\) and \(\text{Ca}^{2+}\) ions. Hence, Statement 3 is true.

- Examine Statement 4

Both temporary and permanent hardness can be removed by washing soda (sodium carbonate). Hence, Statement 4 is true.

Key concepts

Understanding Temporary Hardness

Temporary hardness in water is mainly caused by the presence of bicarbonates of calcium (Ca(HCO₃)₂) and magnesium (Mg(HCO₃)₂). This type of hardness can be removed by boiling the water. When water is boiled, the bicarbonates are converted into insoluble carbonates, which can then be easily filtered out. A key characteristic of temporary hardness is that it does not stay in the water permanently and is relatively easy to treat.

Understanding Permanent Hardness

Permanent hardness is caused by the presence of chlorides and sulfates of calcium (CaCl₂, CaSO₄) and magnesium (MgCl₂, MgSO₄) in the water. Unlike temporary hardness, permanent hardness cannot be removed by just boiling the water. These compounds remain dissolved even after boiling, making the water hard. To tackle permanent hardness, special treatment methods are necessary, and we will explore some of these in the next section.

Effective Hard Water Removal Methods

There are several methods to treat both temporary and permanent hardness in water. Here are some common ones:

• Boiling: As discussed, boiling is effective for removing temporary hardness by precipitating out bicarbonates.
• Washing Soda: Adding washing soda (sodium carbonate, Na₂CO₃) can treat both types of hardness. It reacts with calcium and magnesium ions to form insoluble carbonates, which can then be filtered out.
• Ion Exchange Resins: Ion exchange resins can replace the calcium and magnesium ions in hard water with sodium or potassium ions, effectively softening the water.
• Lime Softening: Adding lime (calcium hydroxide) can precipitate out calcium and magnesium ions as their respective hydroxides.
• Reverse Osmosis: This method uses a semi-permeable membrane to remove ions, molecules, and larger particles from drinking water.

These methods provide effective solutions to the problems caused by both temporary and permanent hardness in water. Understanding the appropriate application of each method can ensure that the water is suitably softened for its intended use.