Why do salts containing first group metals don't make water hard?
Answer:
Group one metals (but especially Lithium, Sodium and Potassium) form salts with very high solubilities in water. They generally do not react with soaps or cause scaling (precipitated carbonates) in pipes.
Most other metal ions, but especially Calcium, Barium and Magnesium do not readily form soluble salts. These tend to form divalent cations when in acidic solutions, but precipate in basic solutions (especially those with a high concentration on Carbonate or Hydrogen carbonate).
Most methods of softening water usually rely on ways of replacing multivalent cations with monovalent ones.
Hardness of water depends on the concentrations of metal ions like calcium and magnesium that form insoluble carbonates (sometimes bicarbonates and sulfates) with the CO2 in water.
Group 1 carbonates are all soluble.
Hard water usually results in the precipitation of salts of common soaps, usually called "soap scum". This causes a decrease in the effective concentration of surfactant available for cleaning.
The insoluble salts that form are calcium and magnesium salts of anionic surfactants, and these cations are present in "hard" water. Sodium and potassium salts of most anionic surfactants are soluble and do not interfere with the surfactant concentration.
AS almost all the commonly known salts of thew first group metals are highly soluble in water,and do not lead to any turbidity or precipitation on mixing with water.While some of the salts of other group are either sparingly soluble or insoluble in water and hence show the hardness in water.
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