Carbon and its Compounds — Practice

Question 1

Which of the following solutions of acetic acid in water can be used as a preservative?

Accepted Answer

5-10%

Question 2

The suffix used for naming an aldehyde is

Accepted Answer

-al

Question 3

Acetic acid, when dissolved in water, dissociates into ions reversibly because it is a

Accepted Answer

weak acid

Question 4

Which one of the following hydrocarbons can show isomerism?

Accepted Answer

C4H10

Question 5

Combustion of a hydrocarbon is generally accompanied by the evolution of

Accepted Answer

both heat and light

Question 6

2 ml of ethanoic acid was taken in each of three test tubes A, B and C, and 2 ml, 4 ml and 8 ml of water were added respectively. A clear solution is obtained in

Accepted Answer

all the test tubes

Question 7

If 2 ml of acetic acid is added slowly in drops to 5 ml of water, we will notice

Accepted Answer

formation of a clear and homogeneous solution

Question 8

A few drops of ethanoic acid were added to solid sodium carbonate. The result is

Accepted Answer

brisk effervescence occurred

Question 9

When acetic acid reacts with ethyl alcohol we add conc. H2SO4, which acts as a ......... and the process is called .........

Accepted Answer

dehydrating agent, esterification

Question 10

Why does carbon form compounds mainly by covalent bonding?

Accepted Answer

Because it can neither gain nor lose four electrons easily. To form C4- its nucleus of only six protons would have to hold ten electrons, and its electronegativity is only 2.5, so the anion does not form readily. To form C4+ would require a huge amount of energy, not normally available. Carbon therefore satisfies its tetravalency by sharing four electron pairs.

Question 11

Explain how sodium ethoxide is obtained from ethanol, with the chemical equation.

Accepted Answer

Ethanol resembles a water molecule with a C2H5 group in place of one hydrogen, so like water it reacts with metallic sodium, liberating hydrogen gas and forming sodium ethoxide: 2C2H5OH + 2Na -> 2C2H5ONa + H2.

Question 12

Two carbon compounds A and B have molecular formulae C3H8 and C3H6 respectively. Which one is most likely to undergo addition reactions? Justify your answer.

Accepted Answer

B, C3H6. Applying the general formulae, C3H8 fits CnH2n+2 and so is propane, a saturated alkane, while C3H6 fits CnH2n and so is propene, an unsaturated alkene with a carbon-carbon double bond. Unsaturated compounds undergo addition reactions; saturated ones undergo substitution.

Question 13

Write the possible structural formulae of a compound having the molecular formula C3H6O, give their IUPAC names, and state what is similar about them.

Accepted Answer

Two main structures fit. CH3-CH2-CHO is propanal, an aldehyde. CH3-CO-CH3 is propanone, a ketone, the simplest ketone. What is similar is that both contain the carbonyl group, C=O, and both have the same molecular formula C3H6O, so they are structural isomers of each other.

Question 14

Explain with a chemical equation how an addition reaction is used in the vegetable ghee industry.

Accepted Answer

Vegetable oils have long unsaturated carbon chains and are liquid at room temperature. Hydrogen is added across their double bonds in the presence of a nickel catalyst, which saturates the chains and converts the oil into a solid fat, vegetable ghee. The reaction type is illustrated by CH3-CH=CH-CH3 + H2, with Ni as catalyst, giving CH3-CH2-CH2-CH3. Nickel increases the rate of the reaction without itself finally undergoing any chemical change.

Question 15

Explain the cleansing action of soap.

Accepted Answer

A soap molecule has a polar carboxylate end which is hydrophilic and attracted to water, and a non-polar hydrocarbon end which is hydrophobic and attracted to grease but not to water. When a dirty cloth is put in soap solution, the hydrophobic ends move towards the greasy dirt and attach to it, while the ionic ends stay directed outwards into the water. With a little agitation the dirt is pulled off the cloth, and the soap molecules surround it to form a spherical micelle with the dirt at the centre. These micelles remain suspended in the water like the particles of a colloidal solution, and they do not come together to form a precipitate because each micelle repels the others by ion-ion repulsion. The trapped dirt is therefore rinsed away with the water, and the cloth is left clean.

Question 16

An organic compound X with molecular formula C2H6O undergoes oxidation with alkaline KMnO4 to form compound Y with molecular formula C2H4O2. Identify X and Y, and say what happens when X reacts with Y.

Accepted Answer

X is ethanol, C2H5OH, and Y is ethanoic acid, CH3COOH, which is the compound used as a preservative for pickles. When X reacts with Y in the presence of a few drops of concentrated sulphuric acid and gentle warming, esterification occurs and ethyl acetate is formed, a sweet smelling ester, together with water: CH3COOH + CH3CH2OH -> CH3COOCH2CH3 + H2O.

Practice — Carbon and its Compounds

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