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Heat of Formation

When 12.2 g o...

Question

When 12.2 g of benzoic acid is dissolved in 100 g of water, the freezing point of solution was found to be $- {0.93}^{o} C (K_{f} (H_{2} O) = 1.86 K k g m o l^{- 1})$ . Then the number (n) of benzoic acid molecules associated (assuming 100% association) is

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Solution

$n P h C O O H \to (P h C O O H)_{n}$

$\frac{1}{n} = i$ {As, $α$ =1}

$Δ T_{f} = i \times k_{f} \times m$

$0.93 = \frac{1}{n} \times 1.86 \times \frac{12.2 \times 1000}{122 \times 100}; n = 2$

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