[cuongt]

in some northern hemisphere countries acidic ground water(lakes and rivers) is treated with lime (calcium oxide) to raise the pH of the water. Explain, with the aid of an equation, how lime raises the pH of acidic ground water.

Is the equation:  CaO+H2O----->Ca2+  + 2OH-  ? i think it wrong.
and how can u explain that lime raises the pH of acidic ground water?

[AWK]

This is reaction of synthesis of Ca(OH)2.
Then it can reacts with acids, eg
Ca(OH)2 + H2SO4 = Caso4 + 2H2O
or in ionic form
OH- + H+ = H2O

[cuongt]

wut do u mean synthesis reaction, isnt it just CaO it says lime is added how can u possibly get Ca(OH)2
 

[AWK]

THis is yopur reaction of synthesis
CaO+H2O----->Ca2+  + 2OH-
or CaO + H2O = Ca(OH)2

Ca(OH) is soluble in water to some extent and completely dissociates in water.

[cuongt]

ooooooooooo in other words there are two reactions. this is so hard to understand.

[plu]

Not at all!  Your first equation was very much correct.  CaO will hydrolyse (react with water) to produce Ca²⁺ ions and OH^- ions.  Knowing this, one can clearly see that the OH^- ions will act to raise the pH of the solution (by neutralizing H⁺ ions or simply adding OH^- ions to solution).  You don't need to worry about the solubility of Ca(OH)₂ at all to answer the question.

[AWK]

Not at all!  Your first equation was very much correct.  CaO will hydrolyse (react with water) to produce Ca²⁺ ions and OH^- ions.  Knowing this, one can clearly see that the OH^- ions will act to raise the pH of the solution (by neutralizing H⁺ ions or simply adding OH^- ions to solution).  You don't need to worry about the solubility of Ca(OH)₂ at all to answer the question.

Ca(OH)2 will dissociate !!!

[constant thinker]

Your both right about lime. Lime is a general term. CaO (calcium oxide) is more commonly refered to as quicklime. Ca(OH)₂ (calcium hydroxide) though is called slaked lime. I believe both of them are used in mime that you put on your lawn. It just depends on the company that makes it.

[cuongt]

cool. thanks