Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

Account for the following :

Ozone is thermodynamically unstable.

Calculate the freezing point of solution when 1.9 g of MgCl₂ (M = 95 g mol⁻¹) was dissolved in 50 g of water, assuming MgCl₂ undergoes complete ionization.

(K_f for water = 1.86 K kg mol⁻¹)

When 2.56 g of sulphur was dissolved in 100 g of CS₂, the freezing point lowered by 0.383 K. Calculate the formula of sulphur (S_x).

(K_f for CS₂ = 3.83 K kg mol⁻¹, Atomic mass of sulphur = 32 g mol⁻¹]

Give reasons for the following observations: Lyophilic sol is more stable than lyophobic sol. 

How the supersonic jet aeroplanes are responsible for the depletion of ozone layers?

Calculate the freezing point of the solution when 31 g of ethylene glycol (C₂H₆O₂) is dissolved in 500 g of water.

(K_f for water = 1.86 K kg mol^–1)

Define the following term:

Multimolecular colloids

Define the following term as related to proteins:

Denaturation

Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.

Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.

Calculate the mass of ascorbic acid (Vitamin C, C₆H₈O₆) to be dissolved in 75 g of acetic acid to lower its melting point by 1.5°C. K_f = 3.9 K kg mol⁻¹.

A 5% solution (by mass) of cane sugar in water has freezing point of 271 K. Calculate the freezing point of 5% glucose in water if freezing point of pure water is 273.15 K.

Two elements A and B form compounds having formula AB₂ and AB₄. When dissolved in 20 g of benzene (C₆H₆), 1 g of AB₂ lowers the freezing point by 2.3 K whereas 1.0 g of AB₄ lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg mol⁻¹. Calculate the atomic masses of A and B.

The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.

Calculate the depression in the freezing point of water when 10 g of CH₃CH₂CHClCOOH is added to 250 g of water. K_a = 1.4 × 10⁻³, K_f = 1.86 K kg mol⁻¹.

Suggest two materials other than hydrogen that can be used as fuels in fuel cells.

How are the colloidal solutions classified on the basis of physical states of the dispersed phase and dispersion medium?

Why are hydrophobic sols easily coagulated?

How are colloids classified on the basis of Physical states of components

How are colloids classified on the basis of the nature of the dispersion medium?