[Liz]

Hi,

I am trying to find the equilibrium constant for Ca(HCO₃)⁺ complex ion.

(HCO₃)^2-  +   Ca²⁺     Ca(HCO₃)⁺

I tried to search in my textbook, and on many databases and websites but I could not find the equilibrium constant for the above reaction.
I am not really sure if there are books that tabulates all equilibrium constants for all complex ions or other compounds. I am not really sure what these books are called, since I tried to search in the library with no hope.

I had an idea of finding  :delta: G of this reaction, and by know the temperature I can calculate Keq for this reaction. But I am not really sure if its an appropriate way to interprete Keq by  :delta: G. As well as, I have difficulties finding books related to thermodynamics tabulated data.

Any help is appreciated  .

Thanks,

dondon 

[Himik_1982]

The only constant I've found is for CaCO3 formation. It's 10^3.2.
Question: really exotic equilibrium. What problem are you going to solve?

[macman104]

The only constant I've found is for CaCO3 formation. It's 10^3.2.
Question: really exotic equilibrium. What problem are you going to solve?

More importantly, HCO₃ does not have a -2 charge, it is -1.

[Liz]

Thanks for the correction macman104, that was a typo, the reaction is:
 (HCO₃)^-  +   Ca²⁺      Ca(HCO3)⁺

For the actual question, We had different species and we had to write the charge balance for them. That was not a big deal.
But then we had to write chemical reactions that would give these species in the charge balance, and determine which reaction is going to go to completion. So I was able to find all other equilibrium constants for all the reactions I had except this one.

Other species are: H⁺ , Ca²⁺, Ca(OH)⁺, K⁺, OH^-, HCO₃^-, CO₃^2-, ClO₄^- , Ca(HCO3)⁺

Thanks,

don

[Himik_1982]

Thanks for the correction macman104, that was a typo, the reaction is:
 (HCO₃)^-  +   Ca²⁺      Ca(HCO3)⁺

For the actual question, We had different species and we had to write the charge balance for them. That was not a big deal.
But then we had to write chemical reactions that would give these species in the charge balance, and determine which reaction is going to go to completion. So I was able to find all other equilibrium constants for all the reactions I had except this one.

Other species are: H⁺ , Ca²⁺, Ca(OH)⁺, K⁺, OH^-, HCO₃^-, CO₃^2-, ClO₄^- , Ca(HCO3)⁺

Thanks,

don

Still havn’t got it. Are all ions in one solution? Then to be totally correct one should write also for example complex CaClO4+ (but ClO4- is very “bad” ligand).
 What is «complete» reaction? I was taught it depends on the method you use for reagents  determination. So, in your case even Ca2+ + CO32-=CaCO3 is incomplete. I’m sure you’ll find a lot of Ca in saturated CaCO3 solution without any difficult and precise equipment.

[macman104]

Can you post the whole question, in it's entirety?  I'm not 100% certain I'll be able to answer this for you (equilibrium, and all that has never been my strong suit), but it'll clear up any confusion.

[AWK]

Generally, complexes with oxoanions are rather small.
Fou reaction
Ca(HCO₃)⁺ = HCO₃^-  +   Ca²⁺ 
pK is 1.26 (this is the dissociation constant! - pK = -log(K) )

[Liz]

Here is the full question:

Write a charge balance for a solution containing  H+, OH-, Ca2+, HCO3-, CO3 2-, Ca(HCO3)+, Ca(OH)+, K+, ClO4-.

write chemical reactions showing how all these species might be produced from mixing CaCO3(s), KClO4(s) and H2O(l). Which reactions are likely to go to completion and which are likely to reach equilibrium?

AWK thanks soo much! but could you please post the reference.

don

[macman104]

Read this for a charge balance.

So you are going to have the 3 compounds on the left, and the ions on the right, and then you need to charge balance it, like it shows in the following link:

http://alpha.chem.umb.edu/chemistry/ch311/evans/hw%20ch%2010%202007.pdf

Then you need to devise reactions that will cause all of these species to appear.

I would suggest writing the dissociation reactions for each one, and first and post those.

[AWK]

AWK thanks soo much! but could you please post the reference.

Handbook of analytical Chemistry
Ju. Lurie Mir Publisher Moscow 1975 p.286

[Himik_1982]

AWK thanks soo much! but could you please post the reference.

Handbook of analytical Chemistry
Ju. Lurie Mir Publisher Moscow 1975 p.286

Saw in the bottom of the page...

[Himik_1982]

Generally, complexes with oxoanions are rather small.
Fou reaction
Ca(HCO₃)⁺ = HCO₃^-  +   Ca²⁺ 
pK is 1.26 (this is the dissociation constant! - pK = -log(K) )

There are many exceptions. e.g. CH3COO-, [Fe(SO4)2]-.

[Liz]

Thanks macman104, I already have solved the charge balance and the equations, my only problem was that equilibrium constant.

AWK, Thanks for the reference. I could not find it in my university library lolz, but I was able to find another reference with the same title, but different author. It must have it. I will post the reference and the equilibrium constant from that reference when I have access to it.

CaCO₃ <=> Ca²⁺  + CO₃^2-                 
Ksp1 = 4.5*10^-9
KClO₄ <=> K⁺ + ClO₄^-
Ksp2 = 1.05 *10^-2
CO₃^2- + H₂O <=> HCO₃^- + OH^-
K1 = 2.15 *10^-4
HCO₃^- + Ca²⁺  <=> Ca(HCO₃)⁺
k2 =  0.055
2H₂O <=> OH^- + H₃O⁺
Kw = 1.01 *10^-14
Ca²⁺  +  OH^- <=> Ca(OH)⁺
K3 = 20


OK, now after finding the equilibrium constants for each one of these reactions. I have to determine which one goes to completion. So, can I say its only the last reaction since its K is the only one which is higher than 1?

Thanks all

[Borek]

Strange question. ALL reactions have their own equilibria, and "went to completion" is not a defined term. Imagine reversed situation - you start with calcium and carbonate. Precipitate forms. Did the reaction went to completion, or not?