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Hydrogen

Question
CBSEENCH11006952

When hard water is boiled in electric kettle, a white scale gets formed inside the kettle. How is this scale formed? What is its harm?

Solution
When hard water is boiled in an electric kettle, a white scale is formed inside the kettle. It is due to the formation of calcium and magnesium carbonates.
The name of the clear solution is lime water.
Ca left parenthesis HCO subscript 3 right parenthesis subscript 2 space space rightwards arrow with Heat on top space stack CaCO subscript 3 with left parenthesis Insoluble right parenthesis below space plus space CO subscript 2 space plus space straight H subscript 2 straight O
Mg left parenthesis HCO subscript 3 right parenthesis subscript 2 space rightwards arrow with Heat on top space stack MgCO subscript 3 with Insoluble below space plus space CO subscript 2 space plus space straight H subscript 2 straight O
As the scale formed is a poor conductor of heat, a lot of heat gets wasted.
When CO2 is passed through the clear solution, it becomes milky due to the formation of insoluble calcium carbonate but the milkiness soon disappears since soluble calcium carbonate gets formed.