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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: ajax0604 on August 16, 2014, 02:31:02 AM

Title: Effect on equilibrium when dilution occurs
Post by: ajax0604 on August 16, 2014, 02:31:02 AM
This is a multiple choice question I am trying to solve and I'm not sure whether my logic is correct.

NaOCl dissociates in water to form Na+ and OCl-. The OCl- hydrolyses as follows OCl- + H2O  ::equil:: HOCl + OH-. 100mL of water is added to a 100mL solution of 0.1M NaOCl. When the solution reaches the new equilibrium:
A  [H+] has decreased
B   pH has decreased
C   [HOCl] has increased
D   K has halved

I think the correct answer is B. When the water is added, the concentration of all the species decreases and the position of the equilibrium shifts to the right. This partially opposes the effect of the dilution by forming more OH- but the concentration will still be less than what it was before the disturbance. Does this sound reasonable? Thank you.
Title: Re: Effect on equilibrium when dilution occurs
Post by: Borek on August 16, 2014, 03:00:27 AM
Quote from: ajax0604 on August 16, 2014, 02:31:02 AM
I think the correct answer is B

Good.

Quote
When the water is added, the concentration of all the species decreases

OK

Quote
and the position of the equilibrium shifts to the right

While this is true, I prefer other explanation. Infinitely diluted solution has always pH 7 (that of pure water). Diluting any solution must shift pH in the direction of 7, no matter what the solution contains.