1. Tardigrade
  2. Question
  3. Chemistry
  4. 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° C ( K f( H 2 O )=1.86 K kg . mol -1 ). The number (n) of benzoic acid molecules associated (assuming 100 % association) is

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Q. 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^{\circ} C \left( K _{f}\left( H _{2} O \right)=1.86 K kg \right.$ $mol ^{-1}$ ). The number (n) of benzoic acid molecules associated (assuming $100 \%$ association) is___

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Solution:

$\Delta T _{ f }= i \times k _{ f } \times m$

$0-(-0.93)= i \times 1.86 \times \frac{12.2}{122 \times 100} \times 1000$

$i =\frac{0.93}{1.86}=0.5$

$i =1+\left(\frac{1}{ n }-1\right) \alpha$

$\frac{1}{2}=1+\left(\frac{1}{ n }-1\right) \times 1$

$n =2$