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Topic: Hydrolysis of salts  (Read 5324 times)

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Offline jsmith613

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Hydrolysis of salts
« on: December 16, 2009, 04:11:17 PM »
I was wondering if someone could check my understanding of Hydrolysis.

a) In a reaction where there is a relatively strong acid, and a relatively strong base the equilibrium lies in the middle.
HCl (aq) + NaOH (aq) --> NaCl + H2O
The Na+ ion comes from NaOH which is a strong alkali, SO Na+ is a weak acid
The Cl+ ion comes from HCl which is a strong acid, SO Cl- is a weak base
this means there are so few H+ and OH- ions in solution, that they all react a neutralize to form water

b) In a reaction where there is a relatively strong acid, and a relatively weak base the equilibrium lies towards the left (lower pH).
Example: Na2CO3 in solution
Na2CO3 (aq) --> 2Na+ + CO3-
the Na+ is a weak acid (NaOH is a strong alkali therefore Na+ is a weak acid)
the CO3- is a strong base (CO3- comes from HCO3- which is a weak acid - therefore CO3- is relatively strong)

Therefore the Na+ + H2O --> NaOH + H+ (Please can someone explain why there is little H+)
CO3- + H2O --> HCO3 - + OH- (in this reaction there is excess OH- as the HCO3 - is relativley weak so less H+ is needed)

c) with a strong alkali and a weak acid it is the opposite of b
« Last Edit: December 16, 2009, 04:35:31 PM by jsmith613 »

Offline Borek

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Re: Hydrolysis of salts
« Reply #1 on: December 16, 2009, 05:14:56 PM »
Looks OK.
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Offline savy2020

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Re: Hydrolysis of salts
« Reply #2 on: December 17, 2009, 02:23:57 AM »
...the Na+ is a weak acid (NaOH is a strong alkali therefore Na+ is a weak acid).

....Therefore the Na+ + H2O --> NaOH + H+ (Please can someone explain why there is little H+).
In the quote above,
The first statement explains what you want
:-) SKS

Offline jsmith613

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Re: Hydrolysis of salts
« Reply #3 on: December 17, 2009, 05:17:22 PM »
Quote
...the Na+ is a weak acid (NaOH is a strong alkali therefore Na+ is a weak acid).

....Therefore the Na+ + H2O --> NaOH + H+ (Please can someone explain why there is little H+).
In the quote above,
The first statement explains what you want
so are you saying that becasue Na+ is weak, it results in less H+ ions in solution?

Offline savy2020

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Re: Hydrolysis of salts
« Reply #4 on: December 18, 2009, 01:28:43 AM »
so are you saying that becasue Na+ is weak, it results in less H+ ions in solution?

Yes the equation as you wrote will be more tending to go backward since of Na+ and H+,  Na+ is weaker than H+. and hence can't accept OH- as readily as H+.
:-) SKS

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