Practice Questions Answers 1 => on chapter 2 (SOLUTIONS)

These are "Practice Questions Answers 1 => on chapter 2 (SOLUTIONS)" for 12th class CBSE Board Examinations.

 

Q1- What do you mean by Henry’s Law?

The Henry’s Law constant for oxygen dissolved in water is 4.34×10⁴atm at 25^o C. 

If the partial pressure of oxygen in air is 0.2 atm, under atmospheric pressure conditions.

Calculate the concentration in moles per Litre of dissolved oxygen in water in equilibrium with water air at 25^o C.

Ans.1.  Henry's Law states "the mass of a gas dissolved in a given volume of the liquid at a constant temperature depends upon the pressure which is applied.

Partial pressure of the gas is directly proportional to its mole fraction in solution at particular temperature.

P_A α X_A ; 

K_{H =} Henry’s Law constant

P_A = ( K_H ) × (X_A)

Given,

K_H = 4.34×10⁴atm 

pO₂ = 0.2 atm

      Xo₂= pO₂ / K_H   

      = 0.2 / 4.34×10⁴ =  4.6×10^-6

If we assume 1L solution = 1L water 

no. of moles of water = 1000/18 = 55.5

          

           XO₂ = nO₂  / (nO₂ +  n H₂O )  

                  ~ = nO₂ /nH₂O

 nO₂ = 4.6 X 10^-6 X 55.5 = 2.55 X 10⁴mol M = 2.55 X 10^-4 M.

Q.2. What is Vant Hoff factor?

Ans.2. It is the ratio of normal molecular mass to observed molecular mass. 
            It is denoted as ‘i’ i = Theoretical Molar mass / observed molar mass

  

                   = Observed no. of particles / Actual no. of particles

                   =  Observed colligative property/Theoretical colligative property

Q.3. What is the Vant Hoff factor in K₄[Fe(CN)₆] and BaCl₂ ?
Ans.3.  5 and 3

Q.4. Why the molecular mass becomes abnormal?
Ans.4. Due to association or dissociation of solute in given solvent.

 Q.5. Define molarity?
Ans.5. Molarity is no. of moles per unit volume of solution in Litre.
Molarity (M) =  ( No. Moles of Solute ) /  (Volume of Solution in Litre).

Q.6. How molarity is related with percentage and density of solution ?

Ans.6.  Molarity(M) = (P) x (Percentage of density) x (10/molar mass)

Q.7. What role does the molecular interaction play in the solution of alcohol and water?

Ans.7. Positive deviation from ideal behavior .

Q.8. What is Vant Hoff factor, how is it related with

a. degree of dissociation           b. degree of association

Ans.8.           

a. α  =  ( i – 1 / n-1)         

                      
b. α = ( i -1  /  1 / n  -1)

Q.9. Why NaCl is used to clear snow from roads ?

Ans.9. It lowers f.p of water

Q10. why the boiling point of solution is higher than pure liquid

Ans.10. Due to lowering in v.