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Question

If 241.5 g of zinc sulphate (ZnSO4) reacts with 81 g of aluminium to give aluminium sulphate. Calculate the mass of the excess reagent left.

3ZnSO4+2AlAl2(SO4)3+3Zn
(take molar mass of Zn as 65 g)

A
27 g
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B
54 g
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C
81 g
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D
161 g
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Solution

The correct option is B 54 g
Given balanced chemical reaction is:
3ZnSO4+2AlAl2(SO4)3+3Zn

The molar mass of ZnSO4=65+32+64=161 g/mol

So, 241.5 g ZnSO4=241.5161 mol=1.5 mol ZnSO4
Again, 81 g Al=8127 mol=3 mol Al

From the balanced chemical equation,
3 moles of ZnSO4 reacts with 2 moles of Al.

Thus, 1.5 moles of ZnSO4 will react with 1 mole of Al.

We are given 3 moles of Al.

Thus, the excess reagent here is Al.
Amount of excess Al=31 mol=2×27 g=54 g

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