Solutions: Class 12 Previous Year Questions

Solutions questions asked in CBSE board exams

Repeated questions first. Open the free app to see each question as it appeared in the paper, with its marking scheme.

1. Calculate the boiling point of a solution containing 0.61 g of benzoic acid (Molar mass = 122 g mol–1) in 5 g of CS2 in which it dimerises to the extent of 88%. The boiling point and Kb of CS2 are 46.2 C and 2.3 K kg mol–1 respectively. 3 { } 14 25. D-…
   Board 20263 marksshort answer
2. Which of the following solutions will have the lowest freezing point in water ? 1 (A) 0.1 M Glucose (B) 0.1 M CaCl2 (C) 0.1 M KCl (D) 0.1 M Urea
   Board 20261 markMCQ
3. Osmosis is a process by which the molecules of a solvent pass from a solution of low solute concentration to a solution of high solute concentration through a semi-permeable membrane. Osmotic pressure is a colligative property. When the applied pressure on a s…
   Board 20264 marksshort answer
4. Compound ‘X’ with molecular formula C4H9Br reacts with aqueous KOH to give an alcohol. The rate of this reaction depends only on the concentration of the compound ‘X’. When an optically active isomer ‘Y’ of the compound ‘X’ was treated with aqueous KOH solutio…
   Board 20263 marksshort answer
5. What type of deviation from Raoult’s law is shown by a mixture of phenol and aniline ? Give reason. What will happen to the boiling point of the solution on mixing phenol and aniline ?
   Board 20262 marksshort answer
6. Assertion (A) : It is not possible to separate the components of an azeotrope by fractional distillation. 1 Reason (R) : Components of an azeotrope have the same composition in liquid and vapour phase and boil at a constant temperature.
   Board 20261 markAssertion-Reason
7. A solution of glucose (molar mass = 180 g mol-l) in water has a boiling point of 100.20 °C. Calculate the freezing point of the same solution. Molal constants for water K and Kp are 1.86 K kg mol-1 and 0.512 K kg mol-1 respectively.
   Board 20253 marksshort answer
8. The spontaneous flow of the solvent through a semipermeable membrane from a pure solvent to a solution or from a dilute solution to a concentrated solution is called osmosis. The phenomenon of osmosis can be demonstrated by taking two eggs of the same size. In…
   Board 20254 marksshort answer
9. (A) Give reasons : (1 + 1 = 2) (a) Cooking is faster in pressure cooker than in an open pan. (b) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult's law is shown by the resulting solution ? What cha…
   Board 20252 marksshort answer
10. (H$) (i) g_mZ Vmn na O2 J¡g H$s VwbZm _| CO2 J¡g Ob _| A{YH$ {dbo` hmoVr h¡ & BZ_| go {H$gH$m KH H$m ? (ii) O~ é{Ya H$mo{eH$mAm| H$mo 0·9% (Ðì`_mZ/Am`VZ) go A{YH$ gmo{S>`_ Ho$ Obr` {db`Z _| aIm OmVm h¡ V~ CZH$m Am_mn (gmBµO) {H$g àH$ma n[ad{V©V hmoVm h¡ ? (iii…
    Board 20245 markslong answer
11. 283 K na {H$gr {dbm`H$ H$m dmîn Xm~ 100 mm Hg h¡ & Cg VZw {db`Z H$m dmîn Xm~ n[aH${bV H$s{OE {Og_| 283 K na {H$gr à~b {dÚwV-AnKQ>²` AB H$m 1 _mob {dbm`H$ Ho$ 50 _mob _| Kwbm h¡ (`h _mZ br{OE {H$ {dbo` AB h¡) & 3 15 23. Write the reaction involved in the follow…
    Board 20243 marksshort answer
12. A 6% solution of glucose (molar mass = 180 g mol 1) is isotonic with 2 5% solution of an unknown organic substance. Calculate the molecular weight of the unknown organic substance.
    Board 20242 marksshort answer
13. An azeotropic solution of two liquids has boiling point lower than either of them when it : (A) is saturated (B) shows positive deviation from Ra (C) (D)
    Board 20241 markMCQ
14. The relative lowering of vapour pressure of an aqueous solution containing non-volatile solute is 0·0225. The mole fraction of the non-volatile solute is : (A) 0·80 (B) 0·725 (C) 0·15 (D) 0·0225
    Board 20241 markMCQ
15. SECTION B 19. 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.
    Board 20232 marksshort answer
16. The colligative property used for the determination of molar mass of polymers and proteins is : (a) Osmotic pressure (b) Depression in freezing point (c) Relative lowering in vapour pressure (d) Elevation is boiling point
    Board 20231 markMCQ
17. Value of Henry’s constant KH : 1 (a) increases with decrease in temperature. (b) decreases with increase in temperature. (c) increases with increase in temperature. (d) remains constant.
    Board 20231 markMCQ
18. Assertion (A) : Osmotic pressure is a colligative property. Reason (R) : Osmotic pressure is proportional to the molality.
    Board 20231 markAssertion-Reason
19. Given below are two statements labelled as Assertion (A) and Reason (R). Assertion (A): A silver mirror can be created at the wall of a test tube using ethanal. Reason (R): Ethanal can react with Fehling's solution Select the most appropriate answer from the o…
    CBSE practice 2022-231 markAssertion-Reason
20. The following table contains osmotic pressure data for three compounds dissolved in various solvents. Compound Concentration, C (g/L) Osmotic pressure (atm) Cellulose 12.5 0.0021 Protein 28.5 0.0026 Haemoglobin 5 0.0018 (R = 0.083 L bar mol-1 K-1) (a) If the c…
    CBSE practice 2023-245 markslong answer

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