Sample of impure magnesium is reacted wih dilute sulphuric acid to give the respective salt and hydrogen. If 1g of impure sample gave 298.6 cc of hydrogen at s.t.p , calculate the % purity of the sample. 

Asked by johncena9384 | 2nd Oct, 2018, 10:45: PM

Expert Answer:

Impure magnesium is reacted with the dilute sulphuric acid to give magnesium sulphate and hydrogen gas.
 
The reaction is as,
 
Mg  +  H2SO4  →  MgSO4 +  H2 
 
No. space of space moles space space of space straight H subscript 2 space equals space fraction numerator Volume space over denominator 22400 space end fraction

space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 298.6 over denominator 22400 end fraction

No. space of space moles space space of space straight H subscript 2 space end subscript equals space 0.0133 space mol

From space equation comma

1 space mole space of space Mg space gives space 1 space mole space of space straight H subscript 2 space end subscript comma

therefore space space 0.0133 space mol space space of space straight H subscript 2 space end subscript will space require space space 0.0133 space mol space of space Mg

we space know comma
No. space of space moles space equals space fraction numerator Weight over denominator Molecular space weight end fraction

Weight space of space Mg space equals space No. space of space moles cross times space Molecular space weight

space space space space space space space space space space space space space space space space space space space space space equals 0.0133 space cross times space 24

Weight space of space Mg space equals 0.3199 space straight g

Given space weight space of space sample space is space 1 space straight g

0.3199 space straight g space of space sample space is space pure space that space produces space hydrogen space gas

So comma space percent sign space purity space equals fraction numerator Mass space of space pure space sample over denominator Mass space of space sample end fraction cross times 100

space space space space space space space space space space space space space space space space space space space space equals fraction numerator 0.3199 space over denominator 1 end fraction cross times 100

space space space space space space percent sign space purity space space equals space 31.99 space percent sign

space space space space space space space space space space space space space space space space space space space space equals space 32 percent sign
The purity of the sample is 32%
 

Answered by Varsha | 3rd Oct, 2018, 10:46: AM