Question

an alloy of iron and carbon was treated with sulphuric acid in which only iron reacts 2Fe + 3H2SO4?gives Fe2(SO4)3?+3H2. If a sample of alloy weighing 140 g gave 6g of hydrogen what is the percentage of iron in the alloy?

Answer 1

An alloy of iron and carbon was treated with sulphuric acid in which only iron reacts 2Fe + 3H2SO4?gives Fe2(SO4)3?+3H2. If a sample of alloy weighing 140 g gave 6g of hydrogen, percentage of iron in the alloy is 80%

According to the balanced chemical reaction,

2Fe + 3H2SO4 → Fe2(SO4)3 +3H2

we get to know that we obtain 3 moles of hydrogen gas from 2 moles of iron.

Or, in other words, we obtain (3X2 = 6gm) of hydrogen gas from (2X56 = 112gm) of iron.            [Molar mass of H2 and Fe are 2gm and 56gm respectively.]

So, we see that we require 112 gm of iron for the evolution of 6gm of hydrogen gas and we are supplied with a 140gm of alloy (of Fe and C).

So, percentage of iron in this alloy is :

(112/140 X 100)% = 80%

∴ There is 80% iron in the alloy.