Question

The temporary hardness of water due to calcium bicarbonate can be removed by adding (a) \(\mathrm{CaCO}_{3}\) (b) \(\mathrm{CaCl}_{2}\) (c) \(\mathrm{HCl}\) (d) \(\mathrm{Ca}(\mathrm{OH})_{2}\)

Short answer

The temporary hardness of water due to calcium bicarbonate can be removed by adding (d) \(\mathrm{Ca}(\mathrm{OH})_{2}\).

Step-by-step solution

Identify the cause of temporary hardness

Temporary hardness in water is primarily due to the presence of dissolved bicarbonate salts of calcium (Ca) and magnesium (Mg). In this case, we are focusing on calcium bicarbonate.

Understand removal of temporary hardness

Temporary hardness can be removed by converting bicarbonates into carbonates that precipitate out of the water, which can be facilitated by adding a base to the water.

Choose the correct compound to add

Out of the given options, the correct compound to add is calcium hydroxide, \(\mathrm{Ca}(\mathrm{OH})_{2}\), as it will react with calcium bicarbonate to form calcium carbonate, which precipitates out, and water.

Write the chemical reaction

The balanced chemical equation for the reaction between calcium bicarbonate and calcium hydroxide is: \[\mathrm{Ca}(\mathrm{HCO}_{3})_{2} + \mathrm{Ca}(\mathrm{OH})_{2} \rightarrow 2\mathrm{CaCO}_{3}\downarrow + 2\mathrm{H}_{2}\mathrm{O}\] This reaction shows the formation of insoluble calcium carbonate and water, thus removing the temporary hardness.

Key concepts

Calcium Bicarbonate

Calcium bicarbonate, often found in water sources, is the main culprit behind temporary water hardness. This compound dissolves in water and when heated, it decomposes, leading to the formation of calcium carbonate, which precipitates and causes scaling in pipes, boilers, and kettles.

Chemically, calcium bicarbonate is written as \(\mathrm{Ca}(\mathrm{HCO}_3)_2\). It is a soluble salt, which means it lends itself easily to water, making the water 'hard'. This kind of hardness, however, is called 'temporary' because it can be removed by heating the water or by adding certain chemicals, which leads us to the process of water softening through the addition of compounds like calcium hydroxide.

Why is it important to know about calcium bicarbonate? Understanding the composition of this compound and its properties is crucial for effectively treating water hardness. Recognizing its role in water hardness can help students comprehend the principles behind various water softening methods.

Calcium Hydroxide

Calcium hydroxide, commonly referred to as slaked lime, is a key player in the water softening process. Its chemical formula is \(\mathrm{Ca}(\mathrm{OH})_2\) and it exists as a white powdery substance or as a colorless crystal. When added to water containing calcium bicarbonate, it causes a chemical reaction that results in water softening.

How does calcium hydroxide achieve this? The substance acts as a base and reacts with the soluble calcium bicarbonate, converting it into an insoluble form, calcium carbonate (\

Water Softening

Water softening is essential in dealing with the drawbacks of hard water, like poor soap performance, scale buildup in pipes and on appliances, among other issues. Softening water involves removing the calcium and magnesium ions that cause the hardness.There are several methods for water softening, one of which is using calcium hydroxide. This substance, when added to hard water, initiates a precipitation reaction that effectively removes the temporary hardness by converting bicarbonates into carbonates, which are not soluble in water.Why focus on water softening? Grasping this concept helps students understand the importance of chemical processes in everyday life, as softened water is crucial for many household and industrial applications. Knowledge of water softening techniques also lays the groundwork for further studies in environmental science, chemistry, and engineering.