Urgent help with question b4 2morrow's chem exam (1 Viewer)

[sando]

I was just practicing a few questions when i got stuck on this and started to panic:

The following experiment was performed to investigate the relative activity of metals. The beaker initially contained 250mL of 0.050 mol L copper sulfate solution.
After several hours the dark blue colour of the solution had become lighter and a red-brown deposit formed on the piece of zinc metal.

a) Account for the changes observed. Provide a balanced oxidation-reduction equation in your answer.

b) The red-brown deposit was removed from the piece of zinc metal and dried. It was found to weigh 0.325 g.
Calculate the concentration of copper sulfate solution remaining in the beaker???




Immediate help is required as my chem exam is 2morrow !!!! . Im suffering from memory loss

 

[Riviet]

(a) Zn_(s) -> Zn²⁺_(aq) + 2e^-
Cu²⁺_(aq) + 2e² -> Cu_(s)
Zn_(s) + Cu²⁺_(aq) -> Zn²⁺_(aq) + Cu_(s)

The red-brown deposit is the copper that has been displaced in solution by the zinc. Since the zinc has displaced the copper in copper sulfate, the blue colour goes ligher, due to the copper coming out of copper sulfate and forming the deposit on the zinc.

I think this is how you do (b):
n_Cu=M/m
=0.325/63.5

C_{copper sulfate}=n/V
=0.325/(63.5x0.25)
=0.02mol/L

 

[sando]

cool, so i got a) right, but im still not sure on how to go about b). i worked out the # of mol of copper. now wat ???