(D) $\Delta T_f = T_o - T_f = 5.3 - 4.47 = 0.83 \ K$ Molar mass of $C_6H_5CH_2COOH = 136 \ g/mol$ Molality $(m) = \frac{0.223 \ g}{136 \ g/mol} \times

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Phenylacetic acid forms a dimer in benzene.

(D) $\Delta T_f = T_o - T_f = 5.3 - 4.47 = 0.83 \ K$ Molar mass of $C_6H_5CH_2COOH = 136 \ g/mol$ Molality $(m) = \frac{0.223 \ g}{136 \ g/mol} \times \frac{1000}{4.49 \ g} = 0.365 \ mol/kg$ Using $\Delta T_f = i \times K_f \times m$: $i = \frac{\Delta T_f}{K_f \times m} = \frac{0.83}{5.12 \times 0.365} \approx 0.444$ Since $i \approx 0.5$,it indicates that the solute molecules associate to form a dimer in benzene.

Class 12 Chemistry Solutions Abnormal molecular mass

Medium

Pure benzene freezes at $5.3^oC$. $A$ solution of $0.223 \ g$ of $C_6H_5CH_2COOH$ in $4.49 \ g$ of benzene freezes at $4.47^oC$. Given $K_f = 5.12 \ K \ kg/mol$,what can be concluded from this?

A
Phenylacetic acid $(C_6H_5CH_2COOH)$ remains as a monomer in benzene.
B
Phenylacetic acid undergoes partial ionization in benzene.
C
Phenylacetic acid undergoes complete ionization in benzene.
D
Phenylacetic acid forms a dimer in benzene.

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Abnormal molecular mass

$A$ compound $MX_2$ has observed and normal molecular masses $65.6$ and $164$ respectively. Calculate the percentage of ionization of $MX_2$ ............ $\%$

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$A$ $0.004 \ M$ solution of $Na_2SO_4$ is isotonic with a $0.010 \ M$ solution of glucose at the same temperature. The apparent degree of dissociation of $Na_2SO_4$ is $..... \ \%$.

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The freezing point of benzene decreases by $0.45 ^\circ C$ when $0.2 \ g$ of acetic acid is added to $20 \ g$ of benzene. If acetic acid associates to form a dimer in benzene,the percentage association of acetic acid in benzene will be .......... $\%$
$(K_f \text{ for benzene} = 5.12 \ K \ kg \ mol^{-1})$

DifficultJEE MAIN 2017

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$2 \,g$ of benzoic acid $(C_{6}H_{5}COOH)$ dissolved in $25 \,g$ of benzene shows a depression in freezing point equal to $1.62 \,K$. The molal depression constant for benzene is $4.9 \,K \,kg \,mol^{-1}$. What is the percentage association of the acid if it forms a dimer in the solution?

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For a $0.1 \ M$ $Ba(NO_3)_2$ solution,the van't Hoff factor is $2.74$. The degree of dissociation is ....... $\%$.

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Pure benzene freezes at $5.3^oC$. $A$ solution of $0.223 \ g$ of $C_6H_5CH_2COOH$ in $4.49 \ g$ of benzene freezes at $4.47^oC$. Given $K_f = 5.12 \ K \ kg/mol$,what can be concluded from this?

Similar Questions

$A$ compound $MX_2$ has observed and normal molecular masses $65.6$ and $164$ respectively. Calculate the percentage of ionization of $MX_2$ ............ $\%$

$A$ $0.004 \ M$ solution of $Na_2SO_4$ is isotonic with a $0.010 \ M$ solution of glucose at the same temperature. The apparent degree of dissociation of $Na_2SO_4$ is $..... \ \%$.

$2 \,g$ of benzoic acid $(C_{6}H_{5}COOH)$ dissolved in $25 \,g$ of benzene shows a depression in freezing point equal to $1.62 \,K$. The molal depression constant for benzene is $4.9 \,K \,kg \,mol^{-1}$. What is the percentage association of the acid if it forms a dimer in the solution?

For a $0.1 \ M$ $Ba(NO_3)_2$ solution,the van't Hoff factor is $2.74$. The degree of dissociation is ....... $\%$.

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