Temporary Hardness

Removing Temporary Hardness

Temporary hardness is caused specifically by dissolved magnesium and calcium hydrogencarbonates. It can be removed in two ways.

1. Boiling. Heat converts the soluble bicarbonates into insoluble products, which can then simply be filtered out:

Interestingly, magnesium precipitates as the hydroxide rather than the carbonate — this happens because $Mg(OH)_2$ is less soluble than $MgCO_3$ under these conditions, so it is the hydroxide that comes out of solution. The filtrate remaining after removing these precipitates is soft water. …