Important Questions For Class XII Chemistry, Solved: Test Yourself From Past SQPs

CBSE class XII examination 2024 is around the corner. This is surely the time to focus rather than panic. Concentrate on studies, and you will definitely achieve your goal.

At this time, constant revision of what you have studied is crucial. The questions below will test your preparedness, and also give an idea of the kind of questions that may be asked.

The following important questions of Chemistry Class 12 have been taken from past sample questions papers of CBSE so, rest assured about the authenticity. The answers have been provided at the end.

Q1. Calculate the number of lone pairs on central atom in the following molecule and predict the geometry: XeF4
(2 marks)

Q2. Explain how and why will the rate of reaction for a given reaction be affected when
a. a catalyst is added
b. the temperature at which the reaction was taking place is decreased
(2 marks)

Q3. (a) DNA fingerprinting is used to determine paternity of an individual. Which property of DNA helps in the procedure?
(b) What structural change will occur when a native protein is subjected to change in pH?
(2 marks)

Q4. Define and write an example for the following:
(3 marks)
(a) Broad spectrum antibiotics.
(b) Analgesics

Q5. (a) Can we construct an electrochemical cell with two half-cells composed of ZnSO4 solution and zinc electrodes? Explain your answer.

(b)

CBSE Class 12 Chemistry SQP 2023-24

(c) The cell constant of a conductivity cell is pic. What is the conductivity of 0.01 M solution of an electrolyte at 298 K, if the resistance of the cell is 1000 ohm?

Q6. (a) When a chromite ore (A) is fused with an aqueous solution of sodium carbonate in free excess of air, a yellow solution of compound (B) is obtained. This solution is filtered and acidified with sulphuric acid to form compound (C). Compound (C) on treatment with solution of KCl gives orange crystals of compound (D). Write the chemical formulae of compounds A to D.

(b) Describe the cause of the following variations with respect to lanthanoids and actinoids:
(i) Greater range of oxidation states of actinoids as compared to lanthanoids.
(ii) Greater actinoid contraction as compared to lanthanoid contraction.
(iii) Lower ionisation enthalpy of early actinoids as compared to the early lanthanoids.

(5 marks)

Q7. Answer the following questions:
(3 marks)

a. State Henry¡¯s law and explain why are the tanks used by scuba divers filled with air diluted with helium (11.7% helium, 56.2% nitrogen and 32.1% oxygen)?
b. Assume that argon exerts a partial pressure of 6 bar. Calculate the solubility of argon gas in water. (Given Henry¡¯s law constant for argon dissolved in water, KH = 40kbar)

Q8. You are given four organic compounds ¡°A¡±, ¡°B¡±, ¡°C¡± and ¡°D¡±. The compounds ¡°A¡±, ¡°B¡± and ¡°C¡± form an orange- red precipitate with 2,4 DNP reagent. Compounds ¡°A¡± and ¡°B¡± reduce Tollen¡¯s reagent while compounds ¡°C¡± and ¡°D¡± do not. Both ¡°B¡± and ¡°C¡± give a yellow precipitate when heated with iodine in the presence of NaOH. Compound ¡°D¡± gives brisk effervescence with sodium bicarbonate solution. Identify ¡°A¡±, ¡°B¡±, ¡°C¡± and ¡°D¡± given the number of carbon atoms in three of these carbon compounds is three while one has two carbon atoms. Give an explanation for your answer. (3 marks)

ANSWERS

Ans 1.

Lone pairs : 2, Geometry : Square planar

Ans 2.

(a) The rate of reaction will increase. The catalyst decreases the activation energy of the reaction therefore the reaction becomes faster.
(b) The rate of reaction will decrease. At lower temperatures the kinetic energy of molecules decreases thereby the collisions decrease resulting in a lowering of rate of reaction.

Ans 3.

(a) Replication A sequence of bases on DNA is unique for a person and is the genetic material transferred to the individual from the parent which helps in the determination of paternity.

(b) During denaturation secondary and tertiary structures are destroyed but the primary structure remains intact.

Ans 4.

(a) Broad spectrum antibiotics: Antibiotics which kill or inhibit a wide range of Gram-positive and Gramnegative bacteria. e.g. Chloramphenicol.

(b)Analgesics: Reduce or abolish pain without causing impairement of consciousness, mental confusion, incoordination or paralysis or some other disturbances of nervous system. e.g. Aspirin / paracetamol etc.

Ans 5.

(a) Yes, if the concentration of ZnSO4 in the two half cell is different , the electrode potential will be different making the cell possible.

(b)

CBSE Class 12 Chemistry SQP 2023-24

(c)

CBSE Class 12 Chemistry SQP 2023-24

Ans 6.

(a)

CBSE Class 12 Chemistry SQP 2019-20

(b)
(i) 5f, 6d and 7s levels in actinoids are of comparable energies.
(ii) This is due to poorer shielding by 5f electrons in actinoids as compared to shielding by 4f electrons in lanthanoids.
(iii) In actinoids, 5f electrons are more effectively shielded from the nuclear charge than the 4f electrons of the corresponding lanthanoids. Since the outer electrons are less firmly held, they are available for bonding in the actinoids.

Ans 7.

(a) Henry¡¯s law: the partial pressure of the gas in vapour phase (p) is proportional to the mole fraction of the gas (x) in the solution. The pressure underwater is high, so the solubility of gases in blood increases. When the diver comes to surface the pressure decreases so does the solubility causing bubbles of nitrogen in blood, to avoid this situation and maintain the same partial pressure of nitrogen underwater too, the dilution is done.

(b)

CBSE Class 12 Chemistry SQP 2022-23

Ans 8.

A, B and C contain carbonyl group as they give positive 2,4 DNP test

A and B are aldehydes as aldehydes reduce Tollen¡¯s reagent

C is a ketone, as it contains carbonyl group but does not give positive Tollen¡¯s test C is a methyl ketone as it gives positive iodoform test

B is an aldehyde that gives positive iodoform test

D is a carboxylic acid

Since the number of carbons in the compounds A,B,C and D is three or two

B is CH 3CHO as this is only aldehyde which gives a positive iodoform test

The remaining compounds A, C and D have three carbons

CBSE Class 12 Chemistry SQP 2023-24

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