Organic chemistry

Question 1

Homologous series properties

Answer 1

• same functional group
• common general formula
• prepared by same method
• undergo similar chemical reactions
• each member differs from next by a CH2 group
• show a trend in physical properties

Question 2

What is a Hydrocarbon

Answer 2

Organic compound consisting of hydrogen & oxygen only.

• When burnt completely in air, H2O & CO2 are formed

Question 3

What are isomers

Answer 3

Organic compounds having same molecular formula but different structural formulae ; having same chemical properties but different physical properties

Question 4

Obtaining alkanes

Answer 4

Fractional distillation of crude oil ( petroleum ) in an oil refinery

Question 5

Physical properties of alkanes

Answer 5

1) non-conductors of electricity
2) insoluble in water
3) as we move down the series, increase in Van Der Waals force causes :
- change in state
- increase in MP & BP
- increase in density
- increase in viscocity
- decrease in volatility
- decrease in flammability

Question 6

Chemical properties of alkanes

Answer 6

• combustion reaction
  ( burning in air )
• substitution reactions

Question 7

Obtaining alkenes

Answer 7

• cracking of big alkanes
• dehydration of alcohols

Question 8

Physical properties of alkenes

Answer 8

Same as alkanes

Question 9

Chemical properties of alkenes

Answer 9

• Combustion
• Hydrogenation
• Halogenation
• Hydrogen halides
• Hydration reaction

Question 10

Hydrogenation reaction

Answer 10

Conditions
- nickel catalyst
- 180^C

Question 11

Halogenation reaction

Answer 11

• chlorination reaction
• bromination reaction
• iodination reaction

Question 12

Hydration reaction

Answer 12

Conditions
- phosphoric acid catalyst
- 300^C
- 65atm

Question 13

Test for alkenes

Answer 13

• decolourise aqueous bromine ( red brown -> colourless )

Question 14

Uses of alkenes

Answer 14

-> To make alcohols
Conditions
- H3PO4 catalyst
- 300^C
- 65atm

-> to make plastics

Question 15

Formation of alcohol

Answer 15

• Fermentation of glucose
• Hydration of ethene

Question 16

Physical properties of alcohols

Answer 16

1) soluble in water
2) non-conductors of electricity
3) highly flammable liquids
4) volatile liquids
5) as we move down the series, an increase in Van Der Waals forces causes :
- increase in MP & BP
- increase in density
- increase in viscocity
- decrease in volatility
- decrease in flammability

Question 17

Chemical reactions of alcohols

Answer 17

• Combustion
• Dehydration reaction
• Oxidation reaction
• Esterification reaction
• react with reactive metals to to liberate H2 gas

Question 18

Test for alcohols

Answer 18

• turn acidified K2CR2O7 from orange -> green
• decolourise acidified KMnO4
• give sweet fruity smell when warmed with an organic acid in presence of concentrated H2SO4 catalyst

Question 19

Formation of organic acids

Answer 19

• oxidation of alcohols

Question 20

Chemical reactions of organic acids

Answer 20

• combustion
• react with reactive metals to liberate H2 gas with effervescence
• react with carbonates & bicarbonates to liberate CO2 gas with effervescence
• neutralise metallic oxides ( basic oxides )
• neutralise alkalis
• undergo esterification by warming with alcohols in the presence of few drops of concentrated H2SO4 catalyst ; esters formed ; sweet fruity smell

Question 21

Uses of esters

Answer 21

• perfumes
• solvents
• food flavourings

Question 22

Test for organic acids

Answer 22

• turn blue litmus paper red
• chemical reactions above