[Kdub]

I was told to do the equations for every step for the synthesis of copper and just want to make sure they're right

Equations:
1.  Copper with Nitric Acid:
Cu (s) + 4HNO₃ (aq) --> Cu(NO₃)₂ (aq) + 2NO₂ (g) + H₂O (l)

2. Formation of Cu(OH)2 :
Cu(NO₃)₂ (aq) + 2NaOH (aq) --> Cu(OH)₂ (s) + 2NaNO₃ (aq)

3. Conversion of Cu(OH)2 to CuO:
Cu(OH)₂ (s) + heat --> CuO (s) + H2O (l)

4. Formation of CuSO4 from CuO:
CuO (s) + H₂SO₄ (aq) --> CuSO₄ (aq) + H₂O (l)

5. Formation of Cu from CuSO4:
CuSO₄ (aq) + Zn (s) --> Cu (s) + ZnSO₄ (aq)

6. Removal of Excess Zn with acid:
2HCl (aq) + Zn (s) --> H₂ (g) + ZnCl₂ (aq)

[mike]

I don't get it

What is the experiment? If you are trying to get Cu why do you start with Cu?

[Mitch]

good point  :lolabove:

[Kdub]

its an experiment obviously...synthesis of copper, we start off with copper and go through multiple reactions to recover it and then we calculate percent recovery.

[mike]

Ok cool, the equations look balanced to me.

The only (minor) point is you don't usually include "heat" as a reactant.

Do you only work out the recovery for the final step, or do you do it for each step?

[Kdub]

we do it at the end because during each reation its not copper metal which we want, its other compounds. thanks for checking them over.

[Kdub]

just wondering if anyone could suggest why we would get a vale of over 100% for the recovered copper, other than the fact that there is still water and other solvents remaining after the last heating?
i said if there was not enough zinc to displace ALL the copper, therefore we have a greater mass. any other possibilities?

[mike]

You have a number of steps in your experiment, and each step has the potential to decrease the yield of Cu, or to increase the impurities. One suggestion would be to work out the "yield" for each step as this may give an of whether the reactions are working etc.

How are you collecting the solid copper in the final step? I know that when you add zinc to a solution of Cu2+ solid copper can deposit on the zinc, maybe you are isolating copper coated zinc along with the solid Cu?

[constant thinker]

Ummn how can you get over 100%. Your not addinng any more copper from the beggining. Atleast I can't see where your adding more copper to the process. I think you should check your recovery value because it would most likely be under 100%.

[Kdub]

if you get 100% then you have lost A LOT throughout your reactions. you are always going to get over 100% if you've done everything right. in each reaction you gain impurities. in the end zinc displaces copper ions and therefore you get copper metal in the bottom of the beaker. if you do not use enough zinc to displace ALL the copper, then you have a mixture overall of some zinc + some copper. we measure the recovery copper by decanting the solution and carefully putting the copper in an evaporating dish and lightly heating it till theres no visible water in it. obviously there will always be some left when you have to measure it right away so thats also going to increase your recovery mass.

[mike]

I think you have the answer then. Although I am not sure that I agree with this statement:

you are always going to get over 100% if you've done everything right.

. If you did each step perfectly then there would be no impurities right?

[Kdub]

i doubt that even "perfect" reactions will ultimately rule out any chance of impurities, but i understand what you are saying.

[mike]

Sounds like an interesting experiment. I still think it would be nice to be able to work out yields for each step, then you could work out if most of the impurities are coming from one particular step or each step etc.