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Question: Give equations to show what happens when temporary hard water is treated with slaked lime....

Give equations to show what happens when temporary hard water is treated with slaked lime.

Explanation

Solution

Hard water is defined as the water which consists of soluble chlorides, bicarbonates, and sulphates of calcium and magnesium. Hard water does lather or forms a foam when mixed with soap. Slaked lime is also a hydroxide of Calcium.

Complete answer:
Temporary Hard water shows the presence of salts of calcium and magnesium carbonates. The hardness of the water can be removed by boiling the water. Removing the magnesium or calcium content from the water makes the resultant water soft.
A reaction between temporary hard water and slaked lime i.e. Calcium hydroxide is a way to turn hard water into soft water.
When Temporary hard water reacts with slaked lime, it forms calcium carbonate or magnesium carbonate, and water is formed.
Ca(HCO3)2 + Ca(OH)2 → 2CaCO3 + 2H2OCa{{\left( HC{{O}_{3}} \right)}_{2\text{ }}}+\text{ Ca}{{\left( OH \right)}_{2}}\text{ }\to \text{ 2CaC}{{\text{O}}_{3}}\text{ + 2}{{\text{H}}_{2}}O
Mg(HCO3)2 + Ca(OH)2 → 2MgCO3 + 2H2OMg{{\left( HC{{O}_{3}} \right)}_{2\text{ }}}+\text{ Ca}{{\left( OH \right)}_{2}}\text{ }\to \text{ 2MgC}{{\text{O}}_{3}}\text{ + 2}{{\text{H}}_{2}}O
When the insoluble salts Ca(HCO3)2 Ca{{\left( HC{{O}_{3}} \right)}_{2\text{ }}} and Mg(HCO3)2 Mg{{\left( HC{{O}_{3}} \right)}_{2\text{ }}}are heated with calcium hydroxide, both are converted into their respective carbonates and form a precipitate. The precipitate formed is filtered out to obtain pure soft water.

Additional Information:
Slaked lime which is Calcium hydroxide is also referred to as Clark’s reagent. It converts the bicarbonate form into carbonate form to remove the hardness of the water.
Another method of treating hard water is by heating it. In this way, the bicarbonates are converted into carbonates and water and carbon-di-oxide is also formed as by-products.

Note:
Hard water forms a precipitate when they come in contact with soap. This is how you can identify if the water is hard or soft. As it has mineral content it easily percolates substances such as chalk or limestone which have calcium content in it. Hard water is not preferred for washing the laundry.