JEE MAIN - Chemistry (2020 - 9th January Morning Slot - No. 10)
How much amount of NaCl should be added
to 600 g of water ($$\rho $$ = 1.00 g/mL) to decrease
the freezing point of water to – 0.2 °C ?
______.
(The freezing point depression constant for water = 2K kg mol–1)
(The freezing point depression constant for water = 2K kg mol–1)
Answer
1.74to1.76
Explanation
$$\Delta $$Tf = 0.2o C
$$ \therefore $$ $$\Delta $$Tf = ikf.m
i = 2 for NaCl
$$ \therefore $$ 0.2 = 2$$ \times $$2$$ \times $$$${{{W_{NaCl}} \times 1000} \over {58.5 \times 600}}$$
$$ \Rightarrow $$ WNaCl = $${{58.5 \times 600 \times 0.2} \over {4 \times 1000}}$$ = 1.76 g
$$ \therefore $$ $$\Delta $$Tf = ikf.m
i = 2 for NaCl
$$ \therefore $$ 0.2 = 2$$ \times $$2$$ \times $$$${{{W_{NaCl}} \times 1000} \over {58.5 \times 600}}$$
$$ \Rightarrow $$ WNaCl = $${{58.5 \times 600 \times 0.2} \over {4 \times 1000}}$$ = 1.76 g
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