12th Standard CBSE Chemistry Unit 3 Solution One Mark Question Paper | QB365

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12th Standard CBSE Chemistry Unit 3 Solution One Mark Question Paper

Published on: 24/08/2019

Solution

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Std: 12th Standard CBSE - Chemistry

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Questions:

Generic 2

9 x 2 = 18

Write Vant's Hoff equation. Name the method commonly used measuring osmotic pressure.

Define osmosis and osmotic pressure.

State Henry's law about the solubility of a gas in a liquid.

Under what condition do non - ideal solutions show negative deviations?

What is the boiling point of an azeotrope of non - ideal solution showing positive deviations as compared to the boiling points of its components ?

Define transition temperature in solubility of a solid in a liquid.

Calculate the molality of H₂SO₄ if the density of 10% (w/w) aqueous solution of H₂SO₄ is 1.84 g cm^-3 (Molar mass of H₂SO₄ = 98g mol^-1).

Why is osmotic pressure considered as a colligative property?

In the determination of molar mass of A⁺B^- using a colligative property, what may be the value of van't Hoff factor if the solute is 50% dissociated?

Multiple Choice Question

15 x 1 = 15

10.

A person is considered to be suffering from lead poisoning if its concentration in him is more than 15 micrograms of lead per decilitre of blood. Concentration in parts per billion parts is

(a)

(b)

(c)

100

(d)

1000

11.

The volumes of 4 N HCI and 10 N HCI required to make 1 litre of 6 N HCI are

(a)

0.75 litre of 4 N HCI and 0.25 litre of 10 N HCI

(b)

0.25 litre of 4 N HCI and 0.75 litre of 10 N HCI

(c)

0.67 litre of 4 N HCI and 0.33 litre of 10 N HCI

(d)

0.80 litre of a N HCI and 0.20 litre of 10 N HCI

(e)

0.50 litre of 4 N HCI and 0.50 litre of 10 N HCI

12.

To neutralise completely 20 mL of 0.1 M aqueous solution of phosphorous acid (H₃PO₃), the volume of 0.1 M aqueous KOH solution required is

(a)

10 mL

(b)

20 mL

(c)

40 mL

(d)

60 mL

13.

A 5.5 molal aqueous solution of methyl alcohol, CH₃OH, is supplied. What is the mole fraction of methyl alcohol in the solution ?

(a)

0.190

(b)

0.086

(c)

0.050

(d)

0.100

14.

If two liquids A and B form minimum boiling azeotrope at some specific composition, then .................... .

(a)

A - B interactions are stronger than those between A - A or B - B

(b)

vapour of solution increases because more number of molecules of liquids A and B can escape from the solution.

(c)

vapour pressure of solution decreases because less number of molecules of only one of the liquids escape from the solution.

(d)

A - B interactions are weaker than those between A - A or B - B.

15.

Considering the formation, breaking and strength of hydrogen bond, predict which of the following mixtures will show a positive deviation from Raoult's law?

(a)

Methanol and acetone

(b)

Chloroform and acetone

(c)

Nitric acid and water

(d)

Phenol and aniline

16.

At equilibrium the rate of dissolution of a solid solute in a volatile liquid solvent is ................... .

(a)

less than the rate of crystalisation

(b)

greater than the rate of crystallisation

(c)

equal to the rate of crystalisation

(d)

zero

17.

The van't Hoff factor i for a compound which undergoes dissociation in one solvent and association in other solvent is respectively

(a)

Greater than one and greater than one

(b)

Less than one and greter than one

(c)

Less than one and less than one

(d)

Greater than one and less than one

18.

Four solutions of K₂SO₄ with the concentrations 0.1 m, 0.01 m, 0.001 m and 0.0001 m are available. The maximum value of van't Hoff factor, i, correaponds to.

(a)

0.0001 m solution

(b)

0.001 m solution

(c)

0.01 m solution

(d)

0.1 m solution

19.

If an aqueous solution of glucose is allowed to freeze, then crystals of which will be separated out first ?

(a)

glucose

(b)

water

(c)

both of these

(d)

none of these

20.

The molal freezing point constant of water is 1.86^o C/M. Therefore the freezing point of 0.1 M NaCl solution in water is expected to be

(a)

- 1.86^oC

(b)

- 0.186^oC

(c)

- 0.372^oC

(d)

+ 0.372^oC

21.

12.0g of urea is dissolved in 1 litre of water and 68.4g sucrose is dissolved in 1 litre of water. The relative lowering of vapour pressure of urea solution is

(a)

greater than sucrose solution

(b)

less than sucrose solution

(c)

double that of sucrose solution

(d)

equal to that of sucrose solution

22.

Which one of the following gases has the lowest value of the Henry's law constant ?

(a)

N₂

(b)

(c)

H₂

(d)

CO₂

23.

In which mode of expression, the concentration of solution remains independent of temperature ?

(a)

Molarity

(b)

Normality

(c)

Formality

(d)

Molality

24.

Brass is

(a)

Solid solution

(b)

Liquid solution

(c)

Gas solution

(d)

All of these

Fill up / 1 Marks

3 x 1 = 3

25.

At the same temperature, nitrogen gas is ............... soluble in water than oxygen.

26.

The solubility of a solute decreases with increase of temparature if dissolution is .............. .

27.

Hydrated salts are solutions of ................. in ................ .

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Answers Key:

Generic 2

9 x 2 = 18

Vant's Hoff equation is \(\pi V=c R T\) Berkley and Hartley method is commonly used for measuring osmotic pressure.

The phenomenon of flow of solvent through a semi-permeable membrane from pure solvent to the solution is called osmosis. The excess pressure which must be applied to a solution prevent the passage of solvent into it through semi-permeable membrane is called osmotic pressure.

The Henry's law states that the mass of a gas dissolved per unit volume of the solvent at a given temperature is proportional to the pressure of the gas in equilibrium with the solution.
\( m \propto p \\ \mathrm{m}=\mathrm{kp} \)
where k is proportionality constant.

When the new forces of interaction between the components are greater than those in the pure components.

The boiling point of such an azeotrope is lower than that of its components.

The temperature at which the trend of solubility changes (e.g., first increases and then decreases) is called the transition temperature.

Molality \(=\frac{10 / 98}{90} \times 1000=1.13 \mathrm{~m}\)

Osmotic pressure depends upon the number of particles of solute and noty on the nature of solute, therefore, it is considered as colligative property.

\( \alpha=\frac{i-1}{n-1} \Rightarrow 0.5=\frac{i-1}{2-1} \Rightarrow i=1.5 \\ \left[\alpha=50=0.5, n=2 \quad \because \quad A B \longrightarrow A^{+}+B^{-}\right] \)

Multiple Choice Question

15 x 1 = 15

10.

11.

12.

13.

(b)
0.086

14.

Minimum boiling azeotrope is formed when actual vapour pressure in higher than expected, i.e., solution shows +ve deviation from Raoult's law which is so when A - B interactions are weaker than A - A or B - B interactions.

15.

(a)
Methanol and acetone

16.

At equilibrium, rate of dissolution = rate of crystallisation.

17.

In case of dissociation, i>1 and in case of association, i>1.

18.

Greater the dilution, greater is the dissociation into and hence greater is the van't Hoff factor.

19.

As solute is solid, the solvent, i.e., water will freeze out.

20.

\(NaCl\longrightarrow { Na }^{ + }+{ Cl }^{ - },i=2\\ \Delta { T }_{ f }={ iK }_{ f }m=2\times 1.86\times 0.1={ 0.372 }^{ o }C,\\ { T }_{ f }={ 0.372 }^{ o }C.\)

21.