Organic Chemistry - Compounds

Question 1

What are the four important families of organic compounds?

Answer 1

• the alkanes
• the alkenes
• the alcohols
• the carboxylic acids

Question 2

If the name of an organic compound ends in -ane, which family does it belong to?

Answer 2

the alkanes

Question 3

If the name of an organic compound ends in -ene, which family does it belong to?

Answer 3

the alkenes

Question 4

If the name of an organic compound ends in -ol, which family does it belong to?

Answer 4

the alcohols

Question 5

If the name of an organic compound ends in -oic acid, which family does it belong to?

Answer 5

the carboxylic acids

Question 6

If the name of an organic compound starts with meth-, how many carbon atoms does it have?

Answer 6

one

Question 7

If the name of an organic compound starts with eth-, how many carbon atoms does it have?

Answer 7

two

Question 8

If the name of an organic compound starts with prop-, how many carbon atoms does it have?

Answer 8

three

Question 9

If the name of an organic compound starts with but-, how many carbon atoms does it have?

Answer 9

four

Question 10

If the name of an organic compound starts with pent-, how many carbon atoms does it have?

Answer 10

five

Question 11

If the name of an organic compound starts with hex-, how many carbon atoms does it have?

Answer 11

six

Question 12

What is a functional group?

Answer 12

A functional group is the part of a molecule that largely dictates how the molecule will react.

Question 13

What is a homologous series?

Answer 13

A homologous series is a group of similar compounds that share similar properties due to the presence of the same functional group, and share the same general formula.

As the chain length increases (by 1 each time), m.p. and b.p. increase, viscosity increases and flammability decreases.

Question 14

What are isomers?

Answer 14

Isomers are compounds with the same formula, but different structures.

Question 15

What differences in physical properties are there between linear isomers and branched isomers?

Answer 15

Branched isomers have lower melting/boling points, as the branches make it harder for the molecules to be close to each other, so the intermolecular forces are weaker.

Question 16

What are some key points about the alkanes?

Answer 16

• Simplest family of organic compounds
• Hydrocarbons
• Form a homologous series with the general formula C_<em>n</em>H_2n+2
• C–C bonds are all single bonds, so they are saturated
• Found in petroleum and natural gas
• 1st four are gases, next 12 are liquids, rest are solids (at r.t.p.)
• Generally unreactive, but burn well in good O₂ supply, so are used as fuels
• React with chlorine in sunlight

Question 17

Describe the reaction between alkanes and chlorine.

Answer 17

A substitution reaction can take place bewteen alkanes and chlorine, where a chlorine atom takes the place of a hydrogen atom. If there is enough chlorine, all the hydrogen atoms will be replaced. This reaction can be explosive, but only in sunlight as it is a photochemical reaction: light energy is needed to break the bonds in the chlorine molecules.

Question 18

What are some key points about the alkenes?

Answer 18

• Hydrocarbons
• Form a homologous series, with the general formula C_<em>n</em>H_<em>2n</em>
• Contain the C = C double bond that is their functional group, and so are called unsaturated.
• Made from alkanes by cracking (this also produces hydrogen)
• Much more reactive than alkanes
• Undergo addition reactions.

Question 19

What is cracking?

Answer 19

This is a reaction in which long-chain hydrocarbon molecules are broken down to shorter, more useful molecules containing the C=C double bond using the following steps:

1. The long-chain hydrocarbon is heated to vaporise it
2. The vapour is passed over a hot catalyst
3. Thermal decomposition takes place

Cracking produces more reactive compounds that can have more uses than the original long-chain hydrocarbon.

Question 20

What is an addition reaction?

Answer 20

An addition reaction is one that turns an an unsaturated alkene into a saturated compound.

Question 21

What is polymerisation?

Answer 21

This is an addition reaction where alkene molecules add on to each other to form long-chain compounds called polymers.

Question 22

How can you test whether a hydrocarbon is saturated or unsaturated?

Answer 22

Add the hydrocarbon to an aqueous solution of bromine (which is orange in colour). If a C=C bond is present, an addition reaction takes places and the colour disappears.

Question 23

What are some key points about the alcohols?

Answer 23

• not hydrocarbons
• form a homologous series with the general formula C_<em>n</em>H_2n+1OH
• have the OH functional group

Question 24

How can ethanol be made?

Answer 24

• Fermentation
• Hydration of ethene

Question 25

What are the uses of ethanol?

Answer 25

* Alcohol in alcoholic drinks * Solvent - dissolves many substances that do not dissolve in water; is volatile (suitable for perfume) * Fuel - burns well in oxygen; can be made cheaply from waste plant material; less impact on CO₂ levels

Question 26

What are some key points about the carboxylic acids?

Answer 26

* not hydrocarbons * forms a homologous series with the general formula **C**_n**H**_2n**O***₂ * * has the functional group **COOH**, also known as the carboxyl group

Question 27

How is ethanoic acid formed?

Answer 27

* oxidation of ethanol by fermentation * oxidation of ethanol with acidified potassium mangante(VII)

Question 28

What are some reactions of ethanoic acid that show it is a typical weak acid?

Answer 28

* solution turns litmus red * solution contains H⁺ ions * since only some molecules dissociate in water, ethanoic acid is a weak acid * reacts with metals, bases, and carbonates to form ionic salts

Question 29

How are esters formed?

Answer 29

Esters are compounds formed from the reaction of ethanoic acid with alcohols. * two molecules join to make a larger molecule with the loss of water, so this is a condensation reaction * the reaction is reversible * the alcohol part comes first in the name but second in the formula, e.g. propyl ethanoate is CH₃COOC₃H₇ * esters often have attractive smells