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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Win,odd Dhamnekar on January 08, 2021, 12:02:18 PM

Title: Coupled equilibria question
Post by: Win,odd Dhamnekar on January 08, 2021, 12:02:18 PM

 A 0.125-M solution of Mn(NO₃)₂ is saturated with H₂S([H₂S]=0.10 M). At what pH, does MnS begin to precipitate?

MnS(s) ::equil:: Mn²⁺ (aq) + S^2- (aq) K_sp= 4.3 × 10^-22

H₂S (aq) + 2H₂O (l)  ::equil:: 2H₃O⁺ (aq) + S^2- (aq) K=1.0× 10^-26

  I am now studying coupled equilibria chapter to answer this question.  Your guidance would be helpful.

Title: Re: Coupled equilibria question
Post by: AWK on January 08, 2021, 01:27:45 PM

https://www.chemicalforums.com/index.php?topic=3719.0

Title: Re: Coupled equilibria question
Post by: Win,odd Dhamnekar on January 11, 2021, 03:37:58 AM

 I found the answer to this question on the other chemistry educational website on internet, but i don't understand the meaning of highlighted area. What is K₁ K₂ (H₂S)?

Title: Re: Coupled equilibria question
Post by: mjc123 on January 11, 2021, 05:38:54 AM

K₁ and K₂ are the two ionisation constants of H₂S:
H₂S + H₂O  ::equil:: H₃O⁺ + HS^- K = K₁
HS^- + H₂O  ::equil:: H₃O⁺ + S^2-  K = K₂

Title: Re: Coupled equilibria question
Post by: Win,odd Dhamnekar on January 11, 2021, 09:44:09 AM

 Thanks.