Page 39 - Curriculum Visions Dynamic Book

Removing the scale
A wide range of chemicals has been developed to remove limescale from the kitchen, bathroom, hot water system and boiling elements. They have to remove the lime while being safe on the hands. This means that
most mineral acids cannot be used. However, natural organic acids can be used to
dissolve the scale. Traditionally acetic
acid (vinegar) was used, although
modern descaling powders contain citric acid (the same acid as in citrus fruit).
Dangers of scaling
As the carbonate layer thickens, it
acts like an artificial stone covering, a
sort of cultured stalagmite (see page 14).
But a cover
of stone cannot conduct heat effectively and so
the heating element becomes less efficient. As
heat cannot get away from the element, there is also a risk that the element will overheat and burn out.
insoluble: a substance that will not dissolve.
precipitate: tiny solid particles formed as a result of a chemical reaction between two liquids or gases. Limescale is a precipitate from hard water.
Oxygen
Carbon
Calcium
Hydrogen
Calcium bicarbonate (soluble) when heated
Carbon dioxide
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Soft water
Calcium carbonate (limescale)
EQUATION: Precipitating limescale
Calcium bicarbonate ➪ carbon dioxide + water + calcium carbonate
Ca(HCO3)2(aq) ➪ solution
CO2(g)
+
H2O(l)
+
CaCO3(s) precipitate
 You know you are in a hard-water area if soap gives little lather.