How to calculate what is needed for a displacement reaction to take place.

I asked this on Science forums but this is the basis of my question

I have some Copper Sulfate in solution, along with various metallic elements which should produce a displacement reaction for example

Rough equations@-

• CuSO_4 + Mg => MgSO4 + Cu
• CuSO_4 + Zn => ZnSO4 + Cu
• CuSO_4 + Al => AlSO4 + Cu

If I make up a 0.1 molar solution of Copper Sulfate at 100ml volume I need 2.49g of Copper Sulfate in 100ml water. This is fine.

Now if I wanted to add just enough of one of the above metals to displace all the copper do I calculate as follows

( I could look this up, but I have an idea of how to do this, so am asking to see if I am on the right track)

• 1 M of Copper sulfate weighs 249g
• Mass of copper is 63.54 g then calculating the % composition gives
  • 63.54 / 249 = 0.26 x 100 = 26%

So if I have a 0.1 M solution, and used 2.49 g of the copper sulfate do I then work out what 26% of that is with

• 0.26 x 2.49 = 0.65g

Therefore I need 0.65g of one of the above elements to displace the Copper

I think that I am nearly there with this, but given Magnesium , Aluminium and Zinc all have different weights, do I need to factor in the atomic mass of the element I am using for the displacement ?

Or just weigh out say 0.65g of Magnesium to produce

CuSO4 5H2O (solution) + Mg = MgSO4 (solution) + Cu + H20

I am not quite sure what happens to the 5H_2O here.

Am I right on my thinking here ?

• Science forum question

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