# Homework Help: Compare the Ks0 values of MnCO3(s)

1. Oct 12, 2014

### spooky01

1. The problem statement, all variables and given/known data
compare the Ks0 values of MnCO3(s) in fresh water (I=0) and in estuarine waters (I=0.08) at 25°C. If each of the waters contained a concentration of CO32- equal to 10-6M and MnCO3(s) controls the Mn solubility, what is the Mn2+ concentration in each water? What is the Mn2+ activity in each water?

2. Relevant equations
MnCO3 (s) = Mn2+ (aq) + CO32- (aq)

Ks0 = {Mn2+}{CO32-} / {MnCO3 (s)}

Ks0 = yMn2+[Mn2+] yCO32-[CO32-]

3. The attempt at a solution
Not sure how to start. Any suggestions are greatly appreciated!

2. Oct 12, 2014

### spooky01

Maybe I'm just not understanding what the problem means. Does it mean if [CO32-] is 10-6M and the ratio of CO32- to Mn2+ is 1:1 in the chemical equation then [Mn2+] is also 10-6M? Is this how others are interpreting the problem?

3. Oct 12, 2014

### Staff: Mentor

Calculate concentration of Mn2+ assuming solution is saturated AND concentration of CO32- is 10-6.

4. Oct 12, 2014

### spooky01

Then an ICE table should be used? Something like this?

____________MnCO3 (s)__________Mn2+ (aq)________CO32- (aq)

Initial___________solid______________0_______________10-6M

Change__________-x_______________+x__________________+x

Equilibrium______-x_______________+x______________10-6M + x

5. Oct 13, 2014

### Staff: Mentor

No, no need for ICE table.

Write formula for Ksp. You know Ksp value, you know concentration of CO32-, the only unknown is the concentration of Mn2+. And solving for the concentration of Mn2+ is trivial.

6. Oct 13, 2014

### spooky01

Ksp = [Mn2+][CO32-]
Ksp = [x][x]
x= 10-6M
Ksp = (10^-6M)(10^-6M)
Ksp = 1.0x10^-12

Is this right?

7. Oct 13, 2014

### Staff: Mentor

No, you are doing strange things. That means you are completely confused about something.

First - find Ksp value in the Ksp tables. What is the value?

8. Oct 13, 2014

### spooky01

Ohh I see what you're saying not, Ksp is 2.2 x 10-11.

9. Oct 13, 2014

### Staff: Mentor

Now plug the Ksp and CO32- concentration into Ksp formula, and solve for the only unknown.

10. Oct 13, 2014

### spooky01

Gotcha, that's simple! I was over thinking it. Thank you oh mighty chemistry guy. So in my above equation Ks0 = yMn2+[Mn2+] yCO32-[CO32-], can Ksp be put in for Ks0?

2.2x10^-11 = [Mn2+] (10^-6M)
2.2x10^-5 = [Mn2+]

Last edited: Oct 13, 2014
11. Oct 14, 2014

### Staff: Mentor

As far as I can tell Ksp and Kso are different symbols used for exactly the same constant.

Just in case someone wonder what your equation means. I guess it is

$$K_{sp} = \gamma_{Mn^{2+}}[Mn^{2+}]\gamma_{CO_3^{2-}}[CO_3^{2-}]$$