Chemistry 2010 JAMB Past Questions - Question 13: Permanent hardness of water can be removed by

Correct Answer

C

Explanation

There are several methods to remove permanent hardness from water, each with its own advantages and disadvantages:

**1. Ion exchange:** This is the most common method and involves passing the water through a resin bed containing sodium or potassium ions. These ions exchange places with the calcium and magnesium ions causing hardness, effectively "softening" the water. This method is effective and widely used in homes and industries.

**2. Reverse osmosis:** This method uses pressure to force water through a semipermeable membrane that allows water molecules to pass through but rejects larger molecules and ions, including those responsible for hardness. This method is very effective for removing all types of impurities, including hardness, but requires more energy and can be expensive for larger applications.

**3. Distillation:** This method boils the water, leaving behind the dissolved minerals, including the hardness-causing ones. The steam is then condensed back into water, which is now softened. This method is highly effective but very energy-intensive and impractical for large-scale applications.

**4. Lime-soda softening:** This chemical process uses lime (calcium hydroxide) and soda ash (sodium carbonate) to precipitate the calcium and magnesium ions as insoluble solids, which are then removed through filtration. While effective, this method requires precise chemical dosing and can produce a large amount of sludge depending on the water composition.

**5. Zeolite softening:** This method uses natural zeolite minerals to exchange sodium ions for calcium and magnesium ions, similar to ion exchange resins. It is an eco-friendly alternative but has lower capacity and requires regeneration with salt solutions.

Ultimately, the best method for removing permanent hardness depends on several factors, including water hardness level, desired water quality, cost, and environmental impact. Consult a water treatment specialist to determine the most suitable method for your specific needs.