Q29 of 30 Page 256

When a chromite ore (A) is fused with sodium carbonate in free excess of air and the product is dissolved in water, a yellow solution of compound (B) is obtained. After treatment of this yellow solution with sulphuric acid, compound (C) can be crystallised from the solution. When compound (C) is treated with KCl solution, orange crystals of compound (D) crystallise out. Identify compounds A to D and also explain the reactions.

OR


An oxide of mangnese (A) is fused with KOH in the presence of an oxidizing agent and dissolved in water. A dark green solution of compound (B) is obtained. Compound (B) disproportionates in neutral or acidic solution to give purple compound (C). Alkaline solution of (C) oxidises potassium iodide solution to a compound (D) and compound (A) is also formed. Identify compounds A to D and also explain the reactions involved.


A is FeCr2O4, B is Na2CrO4, C is Na2Cr2O7.2H2O and D is K2Cr2O7.


The reactions are


1.


2.


3.


Thus, A is chromite of iron which when reacts with the sodium carbonate gives a yellow solution (Na2CrO4), which in the presence of the H+ ion (acid) gives compound C (Na2Cr2O7.2H2O) which on treatment with KCl solution gives orange crystal of K2Cr2O7.


OR


A is MnO2, B is K2MnO4, C is KMnO4 and D is KIO3.


The reaction involved is


1.


2.


3.


Thus, the reaction involves these steps and their yields are respectively given.


More from this chapter

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26

A statement of assertion followed by a statement of reason is given. Choose the correct answer out of the option given below each equation.

Assertion : When NaCl is added to water a depression in freezing point is observed.


Reason : The lowering of vapour pressure of a solution causes depression in the freezing point.


 27

A statement of assertion followed by a statement of reason is given. Choose the correct answer out of the option given below each equation.

Assertion : Bond angle in ethers is slightly less than the tetrahedral angle.


Reason : There is repulsion between the two bulky (—R) groups.


 28

Explain why does the enthalpy change of a reaction remain unchanged even when a catalyst is used in the reaction.

OR


With the help of an example explain what is meant by pseudo first order reaction.


 30

An aromatic compound ‘A’ (Molecular formula C8H8O) gives positive 2, 4-DNP test. The compound gives a yellow precipitate of compound ‘B’ on treatment with iodine and sodium hydroxide solution. It does not give Tollen’s or Fehling’s test. On drastic oxidation with potassium permanganate it forms a carboxylic acid ‘C’ (Molecular formula C7H6O2) which is also formed along with the yellow compound in the above reaction. Identify compounds A, B and C and write all the reactions involved.

OR


An organic compud ‘A’ (C3H4) on hyration in presence of H2SO4/HgSO4 gives compound ‘B’ (C3H6O). Compound ‘B’ gives white crystalline product (D) with sodium hydrogensulphite. It gives negative Tollen’s test and positive iodoform’s test. On drastic oxidation ‘B’ gives compound ‘C’ (C2H4O2) along with formic acid. Identify compounds ‘A’, ‘B’ and ‘C’ and explain all the reactions.