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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%
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B
30%
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C
10%
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D
40%
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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 $$KClO_{3}$$ = $$\dfrac{4.9}{122.5} = 0.04$$ moles

Now 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 = $$\dfrac{3}{2}\times 0.04 = 0.06$$ 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 $$KClO_{3}$$

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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