Chemical quantities (AS)

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2Fe(3+) + Zn(2+) --> 2Fe(2+) + Zn
I am carrying out the above experiment.
The known volume of Iron is 100 cm3 at 0.08 mol dm-3.
Zinc must be in excess but how do I find the minimum mass of zinc required in order to justify my choice of 5g?

Corrie writes
 
First of all, I think you have made a mistake in your equation. It should surely be:
2Fe³⁺ + Zn -> 2Fe²⁺ + Zn²⁺
 
So, according to the equation, each mole of Zn reacts with 2 moles of Fe³⁺.
 
How many moles of Fe³⁺ do you have? You need to work this out:
moles Fe³⁺ = volume (in cm³)/1000 x concentration (in mol/dm³).
Let's say the answer is z moles of Fe³⁺.
 
So the minimum number of moles of Zn you will need is z/2. The mass of this amount of Zn will be z/2 x molar mass of Zn.
 

 

 

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updated: 01 December 2006