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Moles again

Q: In a reaction between zinc metal and dil Sulphuric acid, how much zinc wld be needed to completely react with 20cm3of 2M dil sulphuric acid.

A: Moles of H2SO4 = 2 x (20/1000) = 0.04mol
0.04 x 98 (Rmm of H2SO4) = 3.92g
.:. 3.92g of zinc needed ?

This was one method, but i think it might be wrong, so maybe i need to write up an equation.

A v2: Zn + H2SO4 ----> ZnSO4 + H2
Moles of H2SO4 = 2 x (20/1000) = 0.04mol
Zn : H2SO4 ratio = 1:1
.:. Moles of Zn = 0.04

which one is right?

Reply 1

winnie the poo

H2SO4 + Zn = ZnSO4 + H2

20cm = 1/50th of a dcm. Therefore there are 2/50 moles of sulphuric acid.

2/50 = 0.04 moles.

ratio of Zn :h:

2SO4 = 1:1 = 0.04:0.04

mass = number of moles x Ar

0.04 x 65.4 = 2.62g

Your second method seems the most logical to me.

Hope that helps :smile:

Reply 2

belle_27

Ditto the second method looks like the correct one.

Reply 3

Doji

aah thanks winnie, missed outt he last bit because i thought moles was the " how much " ...but it seems mass is more reasonable. Rep on it's way :smile: