Page: 61
1. What would be the electron dot structure of carbon dioxide
which has the formula CO2?
Answer:
2. What would be electron dot structure of sulphur which is
made up of eight atoms of sulphur.
Answer:
Page: 68 – 69
1. How many structural isomers can you draw for pentane?
Answer:
Three. They are n-pentane,
iso-pentane and neo-pentane.
2. What are the two properties of carbon which lead to the
huge number of carbon compounds we see around us?
Answer:
(i) Tetravalency (ii) Catenation.
3. What will be the formula and electron dot structure of
cyclopentane?
Answer:
Molecular formula: C5 H10.
Electron dot structure:
4. Draw the structures for the following compounds:
(i) Ethanoic acid (ii)
Bromopentane
(iii) Butanone (iv)
Hexanal
Answer:
(i) Ethanoic acid (CH3COOH)
(ii) Bromopentane (C5H11Br)
(iii) Butanone (CH3 —
CH2 — COCH3)
(iv) Hexanal (C5H11CHO)
5. How would you name the following compounds?
Answer:
(i) Bromoethane
(ii) Methanal
(iii) 1 – Hexyne
Page: 71
1. Why is the conversion of ethanol to ethanoic acid an
oxidation reaction?
Answer:
Addition of
oxygen to a substance is called oxidation. Here, oxygen is added to ethanol by
oxidising agent (alkaline potassium permanganate or acidified potassium
dichromate) and it is converted into acid.
2. A mixture of oxygen and ethyne is burnt for welding. Can
you tell why a mixture of ethyne and air is not used?
Answer:
Burning of
ethyne in air produces a sooty flame due to incomplete combustion. It is not
enough to melt metals for welding.
Page: 74
1. How would you distinguish experimentally between an
alcohol and a carboxylic acid?
Answer:
|
Test |
Alcohol |
Carboxylic acid |
|
Litmus
test |
No
change in colour. |
Blue
litmus solution turns red. |
|
Sodium
hydrogen carbonate test |
C2H5OH
+ NaHCO3 → No reaction |
CH3COOH
+ NaHCO3 → CH3COONa + H2O + CO2. Brisk
effervescence due to evolution of CO2. |
2. What are oxidising agents?
Answer:
Oxidising
agents are the substances which give oxygen to another substance or remove
hydrogen from a substance. E.g., acidic K2Cr2O7.
It oxidises ethanol into ethanoic acid.
Page: 76
1. Would you be able to check if water is hard by using a
detergent?
Answer:
No, because
detergents can lather well even in hard water. They do not form insoluble
calcium or magnesium salts (scum).
2. People use a variety of methods to wash clothes. Usually
after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a
paddle, scrub with a brush or the mixture is agitated in a washing machine. Why
is agitation necessary to get clean clothes?
Answer:
When the cloth wetted in soap solution is agitated or beaten, the micelles containing oily or greasy dirt get removed from the surface of cloth and go into water.