Help pls. Chemistry?

Question

Tap water contains small amount of calcium hydrogen carbonate. Why does ir produce "scale" when heated? What is the chemical composition of "scale"?

Answer 1

bicarbonates of calcium and magnesium are present in water, along with some dissolved gasses, and suspended solids. The camcium and magnesium bicarbonates break down to carbonates when the water is boiled. In the boiler the following chemical reaction takes place : Calcium Bicarbonate + heat. Calcium Carbonate+carbon dioxide+water. Calcium and magnesium bicarbonate are soluble in water but the carbonates are insoluble and therefore precipitate as a fine white powder. This precipitate will bake unto the heating surface of a boiler and form a scale.

Answer 2

There are two sorts of hardness, and the one you describe is called temporary hardness, because it is reduced by boiling. The calcium hydrogencarbonate forms a calcium carbonate scale when the water is boiled, which might be good for the water, but not good for the kettle! The other form of hardness is permanent hardness, caused by salts such as magnesium sulphate in the water, which don't decompose when the water is boiled.

Answer 3

It causes scale when heated because it becomes insoluble. As the water is heated the CO2 comes out and leaves CaCO3. Some H2O is also produced as the H's combine with excess O

Answer 4

Ca(HCO3)2 on heating gives CaCO3

Ca(HCO3)2 -> CaCO3 + H2O + CO2
& here CaCO3 is the scale.

Note:-
Scales may also be composed of
1. CaSO4
2. Mg(OH)2
3. CaSiO3 Or MgSiO3
depending upon the temperature & pressure conditions .

Answer 5

when we heat water the dissolved carbon dioxide will evolve and that make water pH decrease , so calcium carbonate will be more likely to form and calcium bicarbonate dissolve and form carbonate instead

Answer 6

I believe it is Ca(OH)2, Mg(OH)2.

In reference to scale. Also called a sort of lime deposit.