Class 12 Half Yearly Question Paper – Chemistry

Class 12 Half Yearly Question Paper

Subject: Chemistry

General Instructions:

• All questions are compulsory
• Q I to Q5 carry 1 mark each.
• Q 11 to Q22 carry 3 marks each.
• Q23 is of 4 marks.
• Q24 to,Q26 carry 5 marks each.

Q1. Which of these two CalCI₂ or NaCI will produce Schottky defect if added to AgCl and why?

Q2. Why are aquatic species more comfortable in cold water in comparison to warm water?

Q3. IN the reaction A → B, the graph obtained between concentration of reactant and time is :

What is the order of reaction ?

Q4. Why does PCI₃ fumes in moisture?

Q5. Which one in the following pair undergoes SN reaction faster and why?

Q6. An element (atomic mass = 60) having face-centred cubic: structure has a cell edge of 400 pm. What is its density? [NA = 6.023 X 10²³]

Q7. What mass of ethylene glycol (molar mass = 62) must be added to 5.50kg of water to lower the freezing point of water from O^oC to -10.0^oC? [K_f for water = 1.86K kg mol^-1]

Q8. Give an example of a fuel cell and write the cathode and anode reactions for it.

Q9. Distinguish between:

(a) Face-centred and end-centred unit cell.
(b) Conductor and Insulator (in terms of band theory)

Ql0. (a) Explain the mechanism of the acid catalysed dehydration of an alcohol forming and ether

Q11. Explain the following observations:

(a) Lyophilic colloid is more stable than lyophobic colloid.
(b) Sky appears blue in colour.
(c) Coagulation takes place when NaCI is added to Fe(OH)₃ sol.

Q12. What is the difference between multi molecular and macro molecular colloids? Give one example of each type. How are associated colloids different from these two types of colloids ?

Q13. (a) How is ammonia manufactured industrially?
(b) What happens when cone. H₂SO₄ is added to calcium fluoride?

Q14. An organic compound ‘A’ having molecular formula C4Hg an treatment with dil. H₂SO₄ gives B. ‘B’ on treatment with cone. HCI and anhydrous ZnCI₂ gives back ‘C’ and on treatment with sodium ethonide gives back’ A’. Identify A, B, C & write the equations involved.

Q15. Carry out the following conversion:

(a) 2-chloropropane to I-propanol
(b) Toluene to benzyl alcohol
(c) Ethyl chloride to propanoic acid

Q16. Account for the following:

(a) Dipole moment of phenol is smaller than methanol.
(b) C-O-C bond angle in ether is slightly greater than the tetrahedral angle.
(c) Phenol is stronger acid than an alcohol.

Q 17. (a) What is an adsorption isotherm? Describe freundlich adsorption isotherm.
(b) What is shape-selective catalysis?

Q18. Define half-life of a reaction. Derive the general expression for the half-life of a first order reaction.

Q19. The rate constants of a reaction at 500K and 700K are 0.02 s^-1 and 0.07 S^-1 respectively. Calculate the values of Ea & A.

Q20. The cell in which the following reaction occurs:

2Fe³⁺(aq) + 2I^–(aq) ⇔ if 2Fe²⁺(aq) + I₂(S) has E^o_cell = 0.236V at 298K. Calculate ΔG^o and the equilibrium constant of the cell reaction.

Q21. (a) Define the following terms:

(i) Van’t Hoff factor
(ii) Colligative properties

(b) Why a solution of chloroform and acetone shows negative deviation from Raoult’ law

Q22. (a) Complete the following reactions:

(b) ALkyl halides, though polar. are immiscible with water.

Q23. We use many types of water purifiers at homes in schools or at place of work. These are being used to kill the bacteria present in tile water. Parents and elders always advice young children to take only the purified water.

(a) State the principle on which the RO purifiers are based.
(b) What is the material used for making membrane used in RO purifiers?
(c) What values are shown by the parents?
(d) Name two disease that are caused by contaminated water.

Q24. (a) The electrical resistance of a column of 0.05mol/l NaoH solution of diameter 1 cm and length 50 cm is 5.55 X 10³ ohm. Calculate its resistivity, conductivity and molar conductivity.

(b) Calculate Λ^o_M for CaCI₂ and MgSO₄ from the following data:

• Λ^o_M (Ca²⁺) = 119.0 S cm² mol^-1
• Λ^o_M (CI^–) = 76.3 S cm² mol^-1
• Λ^o_M (Mg²⁺) = 106 S cm² mol^-1
• Λ^o_M (SO²⁺₄) = 160 S cm² mol^-1

Q25. (a) Complete the following reactions:

(i) C + H₂SO₄ ((conc.) →
(ii) P₄ + NaOH + H₂O →
(iii) SO₃ + H₂SO₄ →

(b) Explain the following:

(i) Phosphorus has a greater tendency for catenation than nitrogen.
(ii) Oxygen is a gas but sulphur is solid.

Q26. (a) Write short notes on:

(i) Kolbe’s reaction
(ii) Lucas tes

(b) How will you distinguish between the following pair of compounds:

(i) Ethanol and Phenol
(ii) Methanol and Ethanol

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