Single Choice

A weak electrolyte $$(AB_2)$$ with formula mass 100 g / mole is dissociated in water upto 50%. The observed molar mass of the electrolyte is:

A$$100$$
B$$\dfrac {200}{3}$$
C$$50$$
Correct Answer
D$$25$$

Solution

The relationship between the Van't Hoff factor and the degree of dissociation is $$i=\dfrac {1- \alpha + n \alpha }{1}$$

Here n is the number of ions obtained on the dissociation of 1 solute molecule.

Substitute values in the above expression.

$$i=\dfrac {1-0.5+3 \times 0.5}{1}=2$$

The relationship between the Van't Hoff factor, the normal molar mass, and the observed molar mass is given below.

$$i=\dfrac {\text {Normal molar mass}}{\text {observed molar mass}}$$.

Substitute values in the above expression.

$$2=\dfrac {100 g/mol}{ \text {observed molar mass}}$$.

Hence, the observed molar mass is $$\dfrac {100g/mol}{2} = 50 g/mol$$.

SIMILAR QUESTIONS

Solutions

A compound $$MX_{2}$$ has observed and normal molar masses 65.6 and 164 respectively. The apparent degree of ionization of $$MX_{2}$$ is:

Solutions

The molecular weight of benzoic acid in benzene as determined by depression in the freezing point method corresponds to:

Solutions

0.0852 g of an organic halide (A) when dissolved in 2.0 g of camphor, the melting point of the mixture was found to be $$167^{\circ}$$C. Compound (A) when heated with sodium gives a gas (B). 280 mL of gas (B) at STP weighs 0.375g. What would be 'A' in the whole process? $$K_f$$ for camphor = 40, m.pt. of camphor = $$179^{\circ}$$C.

Solutions

When a liquid that is immiscible with water was steam distilled at $${\text{95}}{\text{.}}{{\text{2}}^{\text{o}}}{\text{C}}$$ at a total pressure of 748 torr, the distillate contained 1.25 g of the liquid per gram of water. The vapour pressure of water is 648 torr at $${\text{95}}{\text{.}}{{\text{2}}^{\text{o}}}{\text{C}}$$, What is the molar mass of liquid?

Solutions

Acetic acid dissolved in benzene shows a molecular weight of:

Solutions

Benzoic acid dissolved in benzene will show a molecular mass of:

Solutions

Boiling point of chloroform was raised by $$0.323 K$$, when $$0.5143 g$$ of anthracene was dissolved in $$35 g$$ of chloroform. Molecular mass of anthracene is $$\left( {{K_b}\,for\,CHC{l_3} = 3.9\,K\,\,kg\,mo{l^{ - 1}}} \right)$$

Solutions

If the observed and theoretical molecular mass of NaCl is found to be 31.80 and 58.50, then the degree of dissociation of NaCl is:

Solutions

Molecules of ethanoic acid dimerises in benzene due to $$H-$$bonding if all molecules of ethanoic acid associated in benzene then:

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