Page 41 - Curriculum Visions Dynamic Book

How water-softeners work
Although most people are prepared to put up with hard-water problems, it is possible to use a chemical means to soften the water. Water-softening is a method of taking away the substances that cause the water to be hard.
One commonly used method is to pass the water entering the house through a tank containing a filter. Modern filters use a special clay mineral or an artificial resin.
The filter absorbs onto its surface material such as common salt, which will react with the calcium and magnesium compounds.
 The hard water washes over the filter and the sodium and calcium ions exchange until they are in balance. This takes some of the calcium and magnesium ions out
of the water, making it less hard.
ion: an atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge.
resin: resins are natural or synthetic polymers. They can be molded into solid objects or spun into thread.
filter into the water.
exchanges for the sodium in salt... leaving calcium and magnesium behind.
Also...
A compound may be bonded together by strong electrical forces. When such a compound dissolves, it splits up, with each of the parts retaining its own electrical charge.
These charged particles are called ions. Calcium ions and magnesium ions have a positive charge, bicarbonate ions have a negative charge. When they re-form into a compound, it will be a neutral substance called a salt.
Water-softening treatments rely on the way that ions can be swapped in and out of a solution.
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
 This water-softener passes the incoming hard water over artificial resin spheres.
Magnesium
and calcium
ions left in
filter. by flushing it with salt. This exchanges calcium
From time to time the filter is recharged and magnesium ions for sodium ions.
EQUATION: Water-softening
Hard water (water containing calcium
Sodium ions
pass out of the and magnesium compounds in solution)...