Alcohols

Question 1

How does branching affect boiling point of alcohols?

Answer 1

Boiling point decreases as branching increases.

Reason: branching gives the molecules a more spherical shape leading to lower surface area for Van der Waal’s interaction and hence reduce the Van der Waal’s forces between molecules.

Question 2

Alcohols boiling point in comparison to corresponding Alkane with same number of carbon atoms?

Answer 2

Alcohols have higher boiling points than corresponding Alkanes with the same number of carbon atoms.

Question 3

Why do alcohols have a higher boiling point in comparison to Alkanes with the same number of carbon atoms?

Answer 3

Each alcohol molecule contains a highly polar hydroxyl group which leads to stronger hydrogen bonding between molecules of alcohols compared with Van der Waal’s forces found between Alkane molecules.

Question 4

Are alcohols soluble in water?

Answer 4

Yes. Presence of hydroxyl group enables hydrogen bonds to be formed with water molecules (exothermic reaction)

Question 5

How is solubility affected by increase in molecular size?

Answer 5

Alcohols are relatively soluble in water. Solubility decreases as molecular size increases.

Solubility decreases as the length of the carbon chain increases, the polar hydroxyl group becomes an ever smaller part of the molecule, which becomes more like a hydrocarbon

Question 6

How is alcohol manufactured?

Answer 6

Alcohols are made from glucose by fermentation

Question 7

What is fermentation?

Answer 7

Fermentation is a chemical process in which micro organisms such as yeast act on carbohydrates to produce ethanol and carbon dioxide

Ethanol produced is removed from the mixture by fractional distillation

Question 8

What are the conditions required for fermentation?

Answer 8

Temp of 32-35 degrees (enzymes in yeast)

Maximum concentration of ethanol made is 15% otherwise yeast will die

Yeast catalase

Absence of oxygen

Question 9

What happens of oxygen is present during fermentation?,

Answer 9

Yeast will respire aerobically in the presence of oxygen to create water and carbon dioxide

Ethanol will be oxidized to ethanoic acid and hence end product will be ethanoic acid and water

Question 10

How else can ethanol be manufactured?

Answer 10

Through hydration reaction between ethene and steam

Question 11

How can ethene be obtained from ethanol?m

Answer 11

Ethanol is dehydrated with concentrated sulfuric acid acting as a catalyst and dehydrating agent at 170 degrees to form ethene

Reaction type: elimination
Name: dehydration

Question 12

What are the chemical properties of alcohols?

Answer 12

1) Elimination (dehydration)
2) oxidation
3) combustion (both complete and incomplete)

Question 13

What kind of flame is evolved from complete combustion?

Answer 13

Complete combustion produces a clean flame which is blue and non-luminous

Question 14

What happens during oxidation of alcohol?

Answer 14

Alcohols are oxidized to form Carboxylic acids and water

Question 15

What are the two ways in which ethanol is oxidized?

Answer 15

1) oxidizing agent (eg acidified potassium manganate (VII) KMNO4 purple to Colourless or acidified potassium dichromate (VI) K2Cr2O7 orange to green
- contributes 2(O) NOT O2
2) Oxidation of alcohol with oxygen and bacteria in air. Wine or beer turns sour when exposed to air for a few days due to action of bacteria. Ethanoic acid is formed, which is sour

Question 16

What is the effect of increase molecular size on boiling point of alcohols? Why?

Answer 16

Boiling points increase with increase in molecular size.

Reason: increased length of the chain increases the surface area. Attractive forces (Van der Waal’s) between alcohol molecules become stronger as molecules become larger