Science (English Medium) Class 12 - CBSE Important Questions for Chemistry

After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Ritu a class XII student decided to aware others about the adverse effects of these carcinogens in foods. She consultanted the school principal and requested him to instruct canteen contractor to stop selling sandwiches, pizza, burgers and other bakery products to the students. Principal took an immediate action and instructed the canteen contractor to replace the bakery products with some proteins and vitamins rich food like fruits, salads, sprouts etc. The decision was welcomed by the parents and students.

After reading the above passage, answer the following questions:

1) What are the values (at least two) displayed by Ritu?

2) Which polysaccharide component of carbohydrates is commonly present in bread?

3) Write the two types of secondary structure of proteins.

4) Give two examples of water soluble vitamins.

Give a reason for the following observations:

Amino acids behave like salts.

Write the structures of the monomers used for getting the following polymers

Melamine – formaldehyde polymer

Due to hectic and busy schedule, Mr Angad made his life full of tensions and anxiety. He started taking sleeping pills to overcome the depression without consulting the doctor. Mr Deepak, a close friend of Mr. Angad advised him to stop taking sleeping pills and suggested to change his life lifestyle by doing yoga, meditation and some physical exercise. Mr. Angad followed his friend’s advice and after few days he started feeling better.

After reading the above passage, answer the following

(i) What are the values (at least two) displayed by Mr. Deepak?

(ii) Why is it not advisable to take sleeping pills without consulting doctor?

(iii) What are tranquilisers? Give two examples.

What is ferromagnetism?

What type of magnetism is shown by a substance if magnetic moments of domains are arranged in same direction?

An element crystallizes in a f.c.c. lattice with a cell edge of 250 pm. Calculate the density if 300 g of this element contains 2 × 10²⁴ atoms. 

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)

Out of 1 M glucose and 2 M glucose, which one has a higher boiling point and why?

What happens when the external pressure applied becomes more than the osmotic pressure of solution?

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]

Blood cells are isotonic with 0.9% sodium chloride solution. What happens if we place blood cells in a solution containing

(i) 1.2% sodium chloride solution?

(ii) 0.4% sodium chloride solution?

What is the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3^rd of tetrahedral voids?

What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆_mixH for positive deviation?

3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated).

(Given : Molar mass of benzoic acid = 122 g mol⁻¹, K_f for benzene = 4.9 K kg mol⁻¹)

An element with molar mass 27 g mol⁻¹ forms a cubic unit cell with edge length 4.05 ✕ 10⁻⁸ cm. If its density is 2.7 g cm⁻³, what is the nature of the cubic unit cell?

Define the following term

Schottky defect

An element with density 2.8 g cm^–3 forms a f.c.c. unit cell with edge length 4 x 10^–8 cm. Calculate the molar mass of the element.

(Given : N_A = 6.022 x 10²³ mol ^–1)

Define the following terms : Molarity

Define the following term: 

Molal elevation constant (K_b)