Question

On heating $4.9$ g of $KCl{O}_3$, the weight loss is found to be $0.384$ g. The percentage of $KCl{O}_3$, decomposed is:

• A. $20$%
• B. $30$%
• C. $10$%
• D. $40$%

Answer 1

Answer: (A)

$20$%

The balanced equation for the decomposition can be written as:

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

No. of moles of $KCl{O}_3$ = $\frac{4.9}{122.5}=0.04$ moles

Now the weight loss of $KCl{O}_3$ is due to the oxygen gas released.

As shown in equation.
2 moles of $KCl{O}_3$ gives = 3 moles of $O_2$

0.04 moles of $KCl{O}_3$ gives = $\frac{3}{2}\times 0.04=0.06$ moles

0.06 moles of oxygen = $0.06\times 32=1.92$ g of oxygen

1.92 g is the weight loss from $=4.9$ g of $KCl{O}_3$

0.384 g is the weight loss from = $\frac{4.9\times 0.384}{1.92}$ = 0.98 g of $KCl{O}_3$ $=$ Wt. of $KCl{O}_3$ decomposed

$\therefore$ %age decomposition = $\frac{0.98}{4.9}\times 100$ $=20$%.

Hence, option A is correct.