# Calculating what I need for a displacement reaction

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I have some copper sulfate in solution along with various metals which should react and cause a displacement reaction for example

Mg

Zn

Al

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 cooper 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)

So if 1 M of Copper sulfate weighs 249g

if 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

So I need 0.65g of one of the above metals to displace the copper

I think 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

CuSO_4 5H_2O (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 ?

Thanks

Paul

Edited by paulsutton
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• 2 months later...

Use 0.1 mol of the other metal compound that will react with the 0.1 mol copper sulfate solution for a stoichiometric double displacement rxn (as long as both starting reagents are 1:1 in the balanced equation).

EDIT: Just do what you did for the copper sulfate solution for the other metal compound: "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. "

Edited by Bkhan3
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For metal hydrates, you just need to use the correct molar mass (the anhydrous form and the hydrated forms have different molar masses) when weighing amounts.  For example, if you are weighing 0.1 mole of anhydrous CuSO4 use its molar mass (0.1 mol x 159.60 gmol-1 = 15.96 g).  If you are weighing 0.1 mole of the pentahydrate (0.1 mol x 249.69 gmol-1 = 24.97 g). They both contain the same amount of copper.

Edited by Bkhan3

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