Chemistry CBSE 12 Important Numerical Questions 2025

1

The vapour pressure of pure liquid X and pure liquid Y at 25 °C are 120 mm Hg and 160 mm Hg respectively. If equal moles of X and Y are mixed to form an ideal solution, calculate the vapour pressure of the solution.

140 mm of HG

2

An antifreeze solution is prepared by dissolving 31 g of ethylene glycol (Molar mass = 62 g mol^-1) in 600 g of water. Calculate the freezing point of the solution. (K, for water = 1.86 K kg mol^-1).

Tf= 27145

3

Calculate the mass of ascorbic acid (Molar mass = 176 g mol^-1) to be dissolved in 75 g of acetic acid, to lower its freezing point by 1.5°C. (K, = 3.9 K kg mol^-1) 

Wb=5.077g

4

Calculate the mass of ascorbic acid (Molar mass = 176 g mol ^-1) to be dissolved in 75 g of acetic acid, to lower its freezing point by 1.5°C. (K, = 3.9 K kg mol ^-1)

17.46 mm

5

30 g of urea (M = 60 g mol ^-1) is dissolved in 846 g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.

23.5

6

Ishan's automobile radiator is filled with 1.0 kg of water. How many grams of ethylene glycol (Molar mass = 62 g mol-1) must Ishan add to get the freezing point of the solution lowered to -2.8 °C. (K, for water is 1.86 K kg mol ^-1)

Wb = 93.33 g

7

A 0.01 m aqueous solution of AlCla freezes at -0.068 °C. Calculate the percentage of dissociation. (Given : K, for water = 1.86 K kg mol ^-1]

88.3%

8

Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K,so, in 2 litres of water at 25°C assuming it to be completely dissociated. (Atomic masses: K = 39 u, S = 32 u, 0 = 16 u)

5.27 x 10-3

9

A first order reaction is 40% complete in 80 minutes. Calculate the value of rate constant (k). In what time will the reaction be 90% completed? 

(Given : log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021, log 5 = 0.6771, log 6 = 0.7782]

360

10

For the reaction : 2N₂O₅(g) → 4NO₂(g) + O₂(g) at 318 K Calculate the rate of reaction if rate of disappearance of N₂O₅(g) is 1.4 × 10^-3Ms -1?

7x10 ^-4Ms^-1