Important Questions

CBSE Guess > Papers > Important Questions > Class XII > 2010 > Chemistry > Chemistry By Ms. Mohini Belani

CBSE CLASS XII

Q. 1. An aqueous solution of a gas (X) shows following reactions:

  1. It turns red litmus blue.
  2. When added in excess to a copper sulphate solution, a deep blue colour is obtained.
  3. On addition of ferric chloride solution a brownish precipitate soluble in HNO3 is obtained. Identify (X) and give equations for the reactions in step (ii) and (iii).

Q. 2. A black powder when heated with NaCl and conc. H2SO4 gives off a greenish yellow gas. The gas on passing through liquor ammonia liberates nitrogen and on passing through boiling KOH yields compounds one of which when heated with the black powder evolves oxygen.. Name the gas and the black powder. Explain the chemical reactions involved with equations.

Q. 3. A mixture of three gases A, B and C is passed first through acidified K2Cr2O7 solution when A is absorbed turning K2Cr2O7 solution green. Remainder is passed through excess of lime water which turns milky resulting in absorption of B. The residual gas C is absorbed in alkaline pyrogallol solution. Identify A, B and C.

Q. 4. A white waxy solid (A) when burnt in air forms a compound (B). Element (A) on heating in the excess of a gas (C) gave a compound (D). Compound (D) fumes in moist air and oxidizes metals like silver and tin. Compound (D) on heating decomposes to give back gas (C). Identify A, B, C and D and write the reactions involved.

Q. 5. A monobasic acid (A) which is formed by the reaction between an element (X) and an alkali act as reducing agent. It reduces silver nitrate to silver and is itself oxidized to tribasic acid (B). Tribasic acid (B) on heating give another acid (C )which is tetra basic. Identify A, B, C , X and write the reactions involved.

Q. 6. A white inorganic powder (A) which sublimes when treated with another white compound (B) gives a gas (C). Gas (C) on reaction with another gas (D) which is highly inflammable gives compound (E). Compound (E) is also obtained when compound (A) reacts with another compound (F). Compound (F) turns milky when carbon dioxide gas is passed through it. Compound (A) gives brown ppt when treated with NaOH and another compound (X). Compound(E) gives dense white fumes with HCl. Identify (A), (B), (C), (D), (E), (F) and (X) and write the reactions involved.

Q. 7. An orange coloured compound (A) on heating gives a gas (B). An element (X) when burnt in the atmosphere of gas (B) gives ionic compound (C). Ionic compound (C) on hydrolysis gives two compounds (D) and (E). Compound (D) gives dense white fumes with HCl and compound (E) when treated with another white compound (F) gives back (D) and (D) on thermal decomposition gives (B). Compound (F) gives endothermic reaction when dissolved in water and compound (E) turns milky when carbon dioxide is passed through it. Identify (A) to (F) and write the reactions involved.

Q. 8. A compound (A) on thermal decomposition gives off gas B which is one of the component of atmosphere. Gas (B) reacts with white waxy solid and gives dense white fumes of compound (C). Compound (C) on reaction with monobasic acid gives two compounds (D) and (E). (E) is colourless solid. Compound (C) on addition with H2O gives tribasic acid (F). Identify (A) to (F) and write the reactions involved. Identify compounds A, B and C and write the reactions involved.

Q. 9. An inorganic iodide (A) on heating with a solution of KOH gives a gas (B) and the solution of a compound (C). The gas (B) on ignition in air gives a compound (D) and water. Copper sulphate is reduced to metal on passing (B) through the solution. A precipitate of the compound (E) is formed on reaction of (C) with copper sulphate solution. Identify (A) to (E) and give chemical equations for the reactions involved.

Q. 10.

  1. Sodium salt of an acid (A) is formed on boiling white phosphorous with NaOH solution.
  2. On passing chlorine through phosphorous kept fused under water, another acid (B) is formed which on strong heating gives metaphosphorous acid.
  3. Phosphorous on treatment with conc. HNO3 gives an acid (C) which is also formed by the action of dilute H2SO4 on powdered phosphorite rock.
  4. (A) on treatment with the solution of HgCl2 first gives a white precipitate of compound (D) and then a grey precipitate of (E). Identify (A) to (E) and write balanced equations for the reactions involved.

Q. 11. A colourless gas (A) with pungent smell is obtained by the reaction of white salt (B) and sodium hydroxide. Gas (A) when passed through aqueous solution of copper sulphate, gave a compound (C). Identify the gas (A). Also mention the property shown by gas (A).

Q. 12. A translucent white waxy solid (A) on heating in an inert atmosphere is converted to its allotropic form (B).Allotrope (A) on reaction with very dilute aqueous KOH liberates a highly poisonous gas (C) having rotten fish smell. With excess of chlorine forms (D) which hydrolyses to compound (E). Identify compounds (A) to (E).

Q. 13. An element ‘A’ exists as a yellow solid in standard state. It forms a volatile hydride ‘B’ which is a foul smelling gas and is extensively used in qualitative analysis of salts. When treated with oxygen, ‘B’ forms an oxide ‘C’ which is a colourless, pungent smelling gas. This gas when passed through acidified KMnO4 solution, decolourises it. ‘C’ gets oxidized to another oxide ‘D’ in the presence of a heterogeneous catalyst. Identify A,B,C,D, and also give the chemical equation of reaction of ‘C’ with acidified KMnO4 solution and for conversion of ‘C’ to ‘D’.

Q. 14. When conc. H2SO4 was added into an unknown salt present in a test tube, a brown gas (A) was evolved. This gas intensified when copper turnings were also added into this test-tube. On cooling, the gas (A) changed into a colourless gas (B).

 

Paper Submitted By : Ms. Mohini Belani
Email Id : [email protected]
Ph No.: 07544-273314