Question

# On heating $$4.9$$ g of $$KClO_3$$, the weight loss is found to be $$0.384$$ g. The percentage of $$KClO_3$$, decomposed is:

A
20%
B
30%
C
10%
D
40%

Solution

## The correct option is B $$20$$%The balanced equation for the decomposition can be written as:$$2KClO_{3} \rightarrow 2KCl + 3O_{2}$$No. of moles of $$KClO_{3}$$ = $$\dfrac{4.9}{122.5} = 0.04$$ molesNow the weight loss of $$KClO_{3}$$ is due to the oxygen gas released.As shown in equation. 2 moles of $$KClO_{3}$$ gives = 3 moles of $$O_{2}$$0.04 moles of $$KClO_{3}$$ gives = $$\dfrac{3}{2}\times 0.04 = 0.06$$ moles0.06 moles of oxygen = $$0.06\times 32 = 1.92$$ g of oxygen 1.92 g is the weight loss from $$= 4.9$$ g of $$KClO_{3}$$0.384 g is the weight loss from = $$\dfrac{4.9\times 0.384}{1.92}$$ = 0.98 g of  $$KClO_{3}$$  $$=$$ Wt. of $$KClO_{3}$$ decomposed$$\therefore$$ %age decomposition = $$\dfrac{0.98}{4.9}\times 100$$ $$= 20$$%.Hence, option A is correct.Chemistry

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