C10 - Organic Reactions

Question 1

what are alkenes

Answer 1

Hydrocarbons which have a double bond between two of the carbon atoms in their chain

Question 2

Why are alkenes called unsaturated

Answer 2

the C=C double bond means that alkenes have fewer hydrogens compared with alkanes with the same number of carbon atoms

Question 3

Why are alkenes more reactive than alkanes

Answer 3

the double bond can open up to make a single bond, allowing the two carbon atoms to bond with other atoms

Question 4

What is the general formula for alkenes

Answer 4

CnH2n

Question 5

What are the first 4 alkenes and their number of carbon atoms

Answer 5

Ethene (2Cs) Propene (3Cs) Butene (4Cs) Pentene (5Cs)

Question 6

What do alkenes combust completely to produce

Answer 6

Water and carbon dioxide

Question 7

what is the equation for incomplete combustion of alkenes and the weaknesses

Answer 7

alkene + oxygen —> carbon + carbon monoxide + water (+energy)

Incomplete combustion results in a smoky yellow flame, less energy released and carbon monoxide is a poisonous gas

Question 8

What is a functional group

Answer 8

an atom or group of atoms that give organic compounds their characteristic reactions (e.g. -OH functional group)

Question 9

How do alkenes usually react

Answer 9

most of the time alkenes react via addition reactions where the carbon-carbon double bond opens up and leaves a single bond and a new atom is added to each carbon

Question 10

What is the alkene reaction with hydrogen (Hydrogenation)

Answer 10

Hydrogen reacts with alkenes to open up the double bond and form the equivalent, saturated alkane. The alkene is reacted with hydrogen in the presence of a nickel catalyst at 60-150C

Question 11

What is alkenes reaction with halogens

Answer 11

The double carbon non hind opens up and each carbon atom is bonded to a halogen atom and the result are saturated molecules.
(E.G. bromine and ethene react to form dibromoethane)

Question 12

How to test for alkenes

Answer 12

When orange bromine water is added to an alkene, the bromine will add across the double bond, making a colourless dibromo-compound so the bromine water gets decolourised

Question 13

What is alkenes reaction with steam

Answer 13

Water is added across the double bond and an alcohol is formed. This must happen using a catalyst, high pressure and a temperature over 100C

Question 14

What is the general formula for an functional group of alcohols

Answer 14

CnH2n+1OH

All alcohols have an -OH functional group and end in ‘ol’

Question 15

What are the first 4 alcohols and their formulas

Answer 15

Methanol (CH3OH)
Ethanol (C2H5OH)
Propanol (C3H7OH)
Butanol (C4H9OH)

Question 16

What is the functional group of carboxylic acids

Answer 16

-COOH and their names end in ‘anoic acid’

Question 17

What are the first 4 carboxylic acids and their formulas

Answer 17

Methanoic Acid (HCOOH)
Ethanoic Acid (CH3COOH)
Propanoic Acid (C2H5COOH)
Butanoic Acid (C3H7COOH)

Question 18

How are esters formed

Answer 18

Esters are formed from an alcohol and carboxylic acid. An acid catalyst is usually used (eg concentrated sulfuric acid).

Alcohol + Carboxylic acid —> ester + water

Question 19

Uses of alcohols

Answer 19

• Used as solvents in industry as they can dissolve things water can dissolve and things water can’t dissolve
• Used as fuels as they burn cleanly, are non-smelly and are flammable
• Used in perfume
• Antiseptics
• Drinks

Question 20

Properties of alcohols

Answer 20

flammable, low boiling and condensing points, low viscosity

Question 21

How to produce ethanol from fermentation

Answer 21

1. Extract glucose from crops
2. Add yeast to glucose
3. Fermentation converts sugar to ethanol
   - 30-40C (optimum temp is 37C)
   - anaerobic conditions
   - slightly acidic solution
   - batch process (stop and start)

glucose —> ethanol + carbon dioxide

It uses cheap equipment, sugar is renewable and is more carbon neutral. However it’s very slow, product is impure, high labour costs as it’s a batch process

Question 22

How to produce ethanol from the hydration of ethene

Answer 22

1. Extract crude oil from the ground
2. Use fractional distillation then cracking to get ethene
3. Hydration (addition of steam):
   - phosphoric acid catalyst
   - high temperature and pressure (300C & 60-70 atmospheres pressure)
   - continuous process

It’s a fast reaction with 95-100% yield and the product is pure.
ethene + water —> ethanol

Question 23

Combustion of alcohols

Answer 23

ethanol + oxygen —> carbon dioxide + water

Question 24

Alcohol reaction with sodium

Answer 24

With ethanol, the sodium effervesces, produces hydrogen gas and gets smaller as it forms a solution of sodium ethoxide.
Their reactions are similar to but not as vigorous as the reaction between sodium and water

Question 25

Oxidation of Alcohols

Answer 25

An alcohol is oxidised to a carboxylic acid when boiled with acidified potassium dichromate. The same reaction takes place is ethanol is left exposed to air as microbes from air produce ethanoic acid

Question 26

Alcohols and water

Answer 26

Methanol, Ethanol, Propanol and Butanol are all soluble in water and their solutions have a neutral pH

Question 27

Carboxylic acids and (metal) carbonates

Answer 27

Carboxylic acids react with carbonates to produce a salt, water and carbon dioxide. The salts formed end in -anoate)

Question 28

Carboxylic acids and water

Answer 28

Carboxylic acids dissolve in water and when they dissolve in water they ionise and release H+ ions resulting in a acidic solution. However, they don’t completely ionise so they just form weak acidic solutions

Question 29

How to make esters

Answer 29

Esters are formed when alcohols react with a carboxylic acid. An acid, usually concentrated sulphuric acid, is used as a catalyst.
alcohol + carboxylic acid —> ester + water

Question 30

Testing for alcohols

Answer 30

Add a few drops of the alcohol to a test tube containing potassium dichromate solution acidified with sulphuric acid. The tube is warmed in a hot water bath and if alcohol is present the orange solution turns green

Question 31

Testing for carboxylic acids

Answer 31

Carboxylic acids react with sodium hydrogen carbonate to produce carbon dioxide gas which will turn limewater cloudy when bubbled through it.

Carboxylic acid will also turn blue litmus paper red

Question 32

Identifying esters

Answer 32

Esters can be identified by their sweet, fragrant odours

Question 33

A what is a homologous series

Answer 33

a group of related organic compounds which have the same functional group (e.g. carboxylic acids)