Home water softeners operate by passing \"hard water, \" which contains calcium
ID: 499526 • Letter: H
Question
Home water softeners operate by passing "hard water, " which contains calcium and magnesium ions, through a column of cation exchange resin in which the following exchange reaction takes place: The calcium and magnesium ions replace the sodium ions on the resin and are hence removed from the water. The sodium ions, of course, are released from the resin and end up taking the place of the calcium and magnesium ion in the water. This type of water-softening system is therefore not recommended for individuals on sodium-restricted diets. About once a week the resin must be regenerated. A saturated solution of NaCl is passed through the resin and all the calcium and magnesium ions are replaced with sodium ions. Use lessthanorequalto Chatelier's principle to explain why the regeneration works despite the fact that the resin binds calcium and magnesium ions much more strongly than sodium ions.Explanation / Answer
Le Chatlier principle is related equlibrium. It states that when equilibrium in a reaction is subjected to change (Temperature, concentration, volume and pressure), it will shift equilibrium to minimize the effects of change.
In above reaction regeneration works in same way as softening. The difference is that concentration of Na ion shifted the equlibrium of the reaction to the left side, that means sodium ions get binded to resin and calcium ions become free- these excess hard water ions are than drained to the waste tank. Then resin is ready to use again for water softening
Since Calcium and magnesium ions are binded strongly than sodium ion but sodium replaces these ions. This is as per Le chatlier principle, addition of excess sodium ions (concentration change to equilibrium) to calcium binded resin needs to be nulified. For this change equilibrium (when no further replacement of calcium ions by sodium ions) is shifted to left by these excess sodium ions.
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