Ion exchange resins - IOE Notes Flashcards
what can these resins be represented by?
Na2R
What happens in the home version/(a) of softening water using ion exchange resin?
When the hard water passes through these resins, the calcium ions (and magnesium ions) that cause the hardness are ‘swapped’ with the sodium ions in the resin, thereby removing the cause of hardness as the calcium ions remain in the resin
what must be done every so often with the ion exchange resin?
eventually the resin becomes full of calcium and magnesium ions and it must be soaked in a concentrated solution of sodium chloride which will replace the calcium ions in the resin with sodium ions. Then it is ready for use again
what must be done every so often with the ion exchange resin?
eventually, the resin becomes full of calcium and magnesium ions and it must be soaked in a concentrated solution of sodium chloride which will replace the calcium ions in the resin with sodium ions. Then it is ready for use again
What is a cation exchange resin?
it exchanges the positive ions in the water (e.g. Ca^2+ and Mg^2+ ions) for Na^2+ ions
What is each Ca^2+ ion in the hard water replaced with when using cation-exchange resin?
each one is replaced by two Na^2+ ions from the resin
Give the chemical equation for the ion-exchange resin removing Ca2+ ions from hardwater
Na2R + Ca^2+ —> CaR + 2na^+
What is another type of exchange resin used to remove all ions in the water (not just the calcium/magnesium ions) to produce deionised water?
This involves two resins, a cation exchange resin and an anion exchange resin
in the production of deionised water, what does the cation exchange resin contain?
it contains H^+ ions which will swap with any positive ions in the water, thus removing the positive ions
in the production of deionised water, what does the anion exchange resin contain?
The anion exchange resin contains OH^- ions which will swap with any negative ions in the water, thus removing the negative ions.
What do the hydroxide and hydrogen ions form when combined together?
the H+ ions combine with the OH- ions to produce water
Is the cation-exchange resin in a water deioniser and a water softener the same?
no
water deioniser –> RH
water softener –> Na2R
what happens after a certain period of time to a water deioniser?
the ion-exchange resin needs to be replaced to ensure that the deioniser is efficiently removing all the ions from the water
Give the formula for what happens with the cation exchange resin in a water deioniser
cation exchange resin:
RH + cation –> H^+ + spent resin
Give the formula for what happens with the anion exchange resin in a water deioniser
anion exchange resin:
ROH + anion –> OH^- + spent resin
