# Solutions VVI Questions

## Q.1. Define osmotic pressure.

Ans- osmotic pressure may be defined as the excess pressure which must be applied to solution in order to prevent flow of solvent into the solution through the semi-permeable membrance. It is denoted by pi.

## Ans- Ideal Solutions :

An ideal solution is that solution in which each component obeys Raoult’s law under all conditions of temperature and concentrations.

An ideal solution will satisfy the following conditions:

1. There will be no change in volume on mixing the two components.

2. There will no change in enthalpy when two components are mixed.

## Non-ideal solution:

A solution which does not obey Raoult’s law is called non-ideal solution.

For example, when we mix  sulfuric acid (solute) in water (solvent) the amount of heat generated is very large and a change in volume is also observed. This is due to formation of a non-ideal solution.

## Q.3. Why does Vapour of a liquid decreases with addition of a non volatile solid solute?

Ans- In a solution containing non-volatile solute, the surface of solution contains both volatile solvent molecules and non-volatile solute molecules. As the Solute is non-volatile, the number of molecules that is escapes from the liquid surface as vapours, decreases. This Result, less number of molecules are now in the Vapour state at a given temperature and results The decrease in vapour pressure of the solvent.

More the amount of non-volatile solute added, Murda lowering in vapour pressure.

Q.4. Define Osmotic pressure.

Ans – Osmotic pressure may be defined as the excess pressure which must be applied to solution in order to prevent flow of solvent into the solution through the semi-permeable membrance. It is denoted by π

π = CRT = n / V RT

C = concentration in molality

R = constant

T = absolute temperature

n = number of moles of solution

V = volume of solution in litres.

Osmotic pressure is a colligative property i.e., It depends upon number of particle of solute present in the solution.

Q.5. Why does vapour pressure of a liqiud decrease with addition of a non volatile solid solute ?

Ans – In a solution containing non-volatile solute, the surface of solution contains both volatile solvent molecules and non-volatile solute molecules. As the solute is non-volatile, the number of molecules that escapes from the liquid surface as vapours, decreases. This results, less number of molecules are now in the vapour state at a given temperature and results the decrease in vapour pressure of the solvent.

More the ammount of non-volatile solute added, more the lowering in vapour pressure.

Q.6. The osmotic pressure of sugar solution is 2.46 atm at 27° C. Calculate the concentration of the solution.

Ans – Given,

Osmotic pressure (π) = 2.46 atm

and temperature (T) = 27 + 273 = 300 k

we know that,   π = CRT,

where,

C = molarity (concentration)

R = Gas constant (=0.81)

Hence, C = π / RT = 2.46 / 0.082 * 300

= 0.1 M

Hence, concentration of solution = 0.1 M

Q.7. How molarity of a solution different from molality ?

Ans – Molarity (M)

Molarity is defined as the number of moles of solute dissolved in one litre or one cubic decimetre of the solution.

Molarity = Moles of solute / Volume of solution (L)

Molality (m)

It is defined as the number of moles of the solute per kilogram of the solvent.

Molality = Moles of solute / Mass of solvent in kg

Thus, molarity is the number of moles of solute per litre of solution while molality is the number of moles of solute per kilogram of the solvent.

## Solutions Objective Question

Q.1. A 5% solution of cane sugar (Mol. Wt = 342) is isotonic with 1% solution of substance X. The molecular weight of X is –

(a) 68.4

(b) 34.2

(c) 171.2

(d) 136.2

Ans – 68.4

Q.2. A solution has an osmotic pressure of 0.0821 atm. at 300 K. Its concentration would be:

(a) 0.66 M

(b) 0.32 M

(c) 0.066 M

(d) 0.033 M

Ans – 0.033 M

Q.3. Azeotropic mixture of HCl and H2O has;

(a) 48% HCl

(b) 22.2% HCl

(c) 36% HCl

(d) 20.2% HCl

Ans – 20.2% HCl

Q.4. If 2gm of NaOH is presnt in 200 ml of its solution, its molarity will be;

(a) 0.25

(b) 0.5

(c) 5

(d) 10

Ans – 0.25

Q.5. Volume of one mole of any gas at NTP is;

(a) 11.2 litre

(b) 22.4 litre

(c) 10.2 litre

(d) 22.8 litre

Ans – 22.4 litre

Q.6. 234.2 gm of sugar syrup contains 342 gm of sugar. What is the molal concentration of the solution ?

(a) 0.1

(b) 0.5

(c) 5.5

(d) 55

Ans – 0.5

Q.7. Which of the following is/are not affected by temperature ?

(a) Molarity

(b) Mole fraction

(c) Molality

(d) Normality

Ans – (b) and (c)

Q.8. Which of the following is not a colligative property ?

(a) Depression in freezing point

(b) Optical activity

(c) Gas dispersed in gas

(d) Elavation of boiling point

Ans – Optical activity