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Standard VIII

Mathematics

The Orthocentre

A 2.0 g sam...

Question

A $2.0$ g sample containing ${N a}_{2} C O_{3}$ and $N a H C O_{3}$ loses $0.248$ g when heated to $300$ $^{o} C$ , the temperature at which $N a H C O_{3}$ decomposes to ${N a}_{2} C O_{3}, C O_{2}$ and $H_{2} O$ . The $%$ of ${N a}_{2} C O_{3}$ in the mixture is (as the nearest integer):

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Solution

On heating, only $N a H C O_{3}$ decomposes.

$2 N a H C O_{3} \to {N a}_{2} C O_{3} + C O_{2} + H_{2} O$

Suppose $a$ g and $b$ g of ${N a}_{2} C O_{3}$ and $N a H C O_{3}$ respectively, are present in the mixture.

$a + b = 2 . . . (i)$

$∵ (2 \times 84)$ g $N a H C O_{3}$ loses $(44 + 18)$ g $C O_{2}$ and $H_{2} O$

$b$ g $N a H C O_{3}$ loses $\frac{(62 \times b)}{(2 \times 84)}$ g $C O_{2}$ and $H_{2} O$

$\frac{62 \times b}{2 \times 84} = 0.248$

$⟹ b = 0.672 g$

By Eq. (i), $a = 1.328 g$

% of ${N a}_{2} C O_{3}$ in mixture $= (\frac{1.328}{2}) \times 100 = 66.4$
So, the nearest integer is $66$ .

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Reactions are:

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A 2.0 g sample containing Na2CO3 and NaHCO3 loses 0.248 g when heated to 300oC, the temperature at which NaHCO3 decomposes to Na2CO3,CO2 and H2O. The % of Na2CO3 in the mixture is (as the nearest integer):

A $2.0$ g sample containing ${N a}_{2} C O_{3}$ and $N a H C O_{3}$ loses $0.248$ g when heated to $300$ $^{o} C$ , the temperature at which $N a H C O_{3}$ decomposes to ${N a}_{2} C O_{3}, C O_{2}$ and $H_{2} O$ . The $%$ of ${N a}_{2} C O_{3}$ in the mixture is (as the nearest integer):