[dasilvd003]

okay I need to calculate the ksp of silver chromate using information from a hypothetical experiment I was given. All I'm given is that 0.01 g of copper is added to a 1 L solution of saturated silver chromate and this is a single dispalcement reaction silver chromate is the limiting reagent. I then need to calculate the % error with regards to the known ksp of silver chromate 1.1 x 10^-12

I don't know if this will make any difference but the mass of coper before the reaction was 1.25 g and after it was 1.24 g. This is the only info given me.

Cu(s) + Ag2CrO4(aq) → CuCrO4(aq) + 2Ag(s) <-this reaction is also given to me

Any help would be appreciated

[Borek]

Calculate concentration of Ag⁺, use it to determine concentration of chromate.

http://www.chemicalforums.com/index.php?topic=45932.0

[ghitz]

I am actually trying to solve this exact same problem.
I've been doing fine so far in this course, and I hate asking for help with things like this, but this question seems to me unanswerable without additional information???

Could you possibly elaborate on your response?
Isn't the Ksp value needed to find the concentration of Ag in the solution?

Im pulling my hair out here, thanks a lot for any help.

[Borek]

You can calculate amount of silver from the reaction with copper. This is just a stoichiometry. Not an obvious one, but the link I posted is to another thread where similar stoichiometric problem was discussed.

[icemann]

Hi there, I am completing this problem too.

I calculated that for copper n=m/M = 0.01g/63.546g/mol = 1.57*10^-4 moles were displaced

According to the balanced equation and stoichiometry 1 mole of copper displaces 2 moles of silver?

Therefore concentration of Ag⁺ in the silver chromate solution would be 2(1.57*10^-4) mol = 3.14*10^-4 because all of it was displaced by the copper in the initial reaction and there is 1.00L of solution.

Because K_sp = [Ag⁺]²[CrO₄^2-] the concentration of Silver ions are twice that of the molar solubility.  The concentration of of Chromate then is the solubility in the 1.00L solution so it is equal to 1.57*10^-4.

Ksp = (3.57*10^-4)^2 * (1.57*10^-4)
      = 1.55*10^-11

Please tell me did I go wrong somewhere is understanding this question?  This value seems very far off the accepted Ksp value of Silver Chromate which the book tells me is 1.1*10^-12.

[Borek]

I calculated that for copper n=m/M = 0.01g/63.546g/mol = 1.57*10^-4 moles were displaced

No. Read the thread I linked to much earlier.

[icemann]

Thanks for reading my addition to the question Borek.  I read the link again.

My question is a little different from the one posted by the original author I suppose.  Mass of Copper before reaction in the silver chromate solution was 1.25g.  The copper was left overnight and then the dark residue which we are told was silver displace from reaction was cleaned off before the copper's mass was remeasured at 1.24g.  So the copper that was displaced in the reaction was 0.1g because the silver chromate that reacted and formed onto the copper was cleaned off?

Maybe my question isn't different but I am failing to understand how the link you provided relates to my question because it seems that mine is different because the silver was cleaned off meaning that I don't have to account for this extra mass when calculating the amount of copper displaced.

Am I on the right track that I am trying find the concentration of silver in the solution by figuring out how much silver was displaced by 0.01g of copper according to the reaction?  The questions actually states that 0.01g of copper reacted..I am sorry that I did not state that earlier.   I think you are saying that a different amount of copper reacted because of the part that you quoted but I cannot figure out the connection between why I am wrong and the link.

I appreciate any help I am lost..

[Borek]

I don't see how the silver can be separated, so my guess was that solid weighted was copper AND silver together. Now that I think about it it doesn't make sense - mass of the solid should be higher.

Stupid question, not only because it makes impossible assumptions, also because 0.01 g mass difference is idiotically inaccurate.

But your calculations are OK - sorry for being wrong earlier. Just note you can't report 1.55e-11, but 2e-11 at best (significant digits).

[icemann]

Thanks again for the help and confirming the calculations.  I guess I could have been more clear about the questions, it just seemed very similar to the first one..

The problem started with a fictional experiment:
Step 1: measure 1.00L of saturated silver chromate
2: clean peice of copper and measure mass (1.25g)
3. place copper in beaker overnight
4.  clean the dark residue off the piece of copper using steel wool and measure mass (1.24g)

There were a couple follow up questions to clarify:  Answers are from book, not mine
What was the dark residue found on piece of copper at end of reaction?
The dark residue was the silver that was displaced from the reaction.
What mass of copper reacted?
0.01g
Why did mass of copper decrease?
copper displace silver.

Then subsequently we are asked to calculate the Ksp of Ag₂CrO₄

I realize now that I should have typed this out for clarity.  Thanks again for helping I appreciate it.