Question

$4.90g$ of impure potassium chlorate on heating shows a weight loss of $0.384g$. What per cent of the impure potassium chlorate has decomposed?

• A. 20
• B. 30
• C. 40
• D. 80

Answer 1

Answer: (A)

Given,

Impure potassium chlorate $=4.90g$

On heating, weight loss $=0.384g$

Equation

$2KCl{O}_3\stackrel{\mathrm{\Delta }}{\to }2KCl+3O_2$

$2$ mol of $KCl{O}_3$ will produce $2$ mol $KCl$ and $3$ mol $O_2$

Molar mass of $KCl{O}_3=122.55g/mol$

Molar mass of $O_2=32g/mol$

$0.384g$ loss$=0.384g{O}_2$ produced

So, produced $O_2=\frac{0.384}{32}=0.012$ mol

That means, decomposed

$KCl{O}_3=0.012\times 2/3=0.008$

Mass of decomposed

$KCl{O}_3=122.55\times 0.008=0.980g$

$\%$ of decomposed $KCl{O}_3=\frac{0.980}{4.9}\times 100=20\%$