- No.4. Explain the oxidation of acetylene.
Answer. Acetylene is oxidized by alkaline KMn04. Hydroxyl groups add to the triple bond to form an intermediate product.
HC≡CH + 2KMnO4 + 2H20 OH OH + 2MnO2 + 2KOH
OH OH -2H2O ║ ║
OH OH Glyoxal
This intermediate product eliminates water molecules to from glyoxal, which on oxidation forms oxalic acid
O O 2[O] O O
OH OH -2H2O ║ ║ KMnO4 ║ ║
H-C—C-H H-C-C-H HO-C-C-OH
OH OH Glyoxal Oxalic acid
This reaction is also used to test the unsaturation in an organic compound.
- No.5. Write balanced chemical equations for the following reactions. Also name the products that formed.
(i) A mixture of ethyne and hydrogen is passed over heated nickel
Answer. When mixture of ethyne and hydrogen is passed over heated nickel at 250-300 °C ethane is formed.
HC≡CH + H2 250-300 C H2C=CH2
H2C=CH2 + H2 250-300 C H3C-CH3
(ii) Ethene is treated with chlorine
Answer. When ethene is treated with chlorine tetrachloroethane is formed.
2CH≡CH + 2C12 Cl Cl
(iii) Ethene is burnt in air
Answer. When ethene is burnt in the presence of excess of air or oxygen carbon dioxide, water and a lot of heat are produced.
2CH=CH+ 5O2 ———> 4CO2+ 2H20 + heat
(iv). Ethene is passed through bromine water
Answer. When ethene is passed through bromine water tetrabromoethane is formed.
HC≡CH + 2Br2 → H-C — C-H
- No.6. Explain briefly.
(i) Why butane undergoes substitution reactions?
Answer. Alkanes are least reactive compound being saturated hydrocarbons they undergo substitution reactions.
CH3-CH2-CH2-CH3 + C12 CH3-CH2-CH2-CH2-C1 + HC1