C10 - Organic Reactions

Question 1

What is an alkene?

Answer 1

• Hydrocarbons with a C=C bond in their chain
• This bond means they have two fewer hydrogen atoms compared with alkanes containing the same number of carbon atoms - this makes the unsaturated.

Question 2

Give the general formula for an alkene.

Answer 2

C(n)H(2n)

Question 3

Why do alkenes burn in air with a smoky flame?

Answer 3

• In enough oxygen - combust completely - produce water and carbon dioxide
• Burnt normally in air - not enough oxygen in air - undergo incomplete combustion:
• alkene + oxygen —> carbon + carbon monoxide + carbon dioxide + water
• Carbon monoxide is poisonous
  (Smoky yellow flame and less energy produced compared to complete combustion of same compound).

Question 4

Name the molecule produces when ethene is hydrogenated.

Answer 4

(Reacted with hydrogen in the presence of a catalyst)

- Produces ethane

Question 5

What is used to test for alkenes?

Answer 5

• Decolourises orange bromine water

- Bromine adds across the double bond, making a colourless dibromo-compound.

Question 6

Give the names and formulas of the first four alcohols.

Answer 6

• Methanol: CH(3)OH
• Ethanol: C(2)H(5)OH
• Propanol: C(3)H(7)OH
• Butanol: C(4)H(9)OH

Question 7

Give the balanced equation for the combustion of methanol.

Answer 7

2CH(3)OH(l) + 3O(2)(g) —> 2CO(2)(g) + 4H(2)O(g)

Question 8

Name the gas that is produced when ethanol reacts with sodium.

Answer 8

Hydrogen

Question 9

Name the process that converts sugar to ethanol using yeast.

Answer 9

• Fermentation
• Sugar –(yeast)-> Ethanol + Carbon dioxide
  (yeast is a catalyst)

Question 10

What is the chemical name of C(2)H(5)COOH?

Answer 10

Propanoic acid

Question 11

Why are carboxylic acids considered weak acids?

Answer 11

=> Dissolve in water - ionise (release H+ ions) - result in acidic solution
=> Don’t ionise completely (not all acid molecules release their H+ ions)
=> Only form weak acidic solutions
=> Have a higher pH (less acidic) than aqueous solutions of strong acids with the same concentration

Question 12

Why are carboxylic acids considered weak acids?

Answer 12

=> Dissolve in water - ionise (release H+ ions) - reulst in acidic solution
=> Don’t ionise completely (not all acid molecules release their H+ ions)
=> Only form weak acidic solutions
=> Have a higher pH (are less acidic) than aqueous solutions of strong acids with the same concentration.

Question 13

Give the general word equation for the reaction of an alcohol and carboxylic acid.

Answer 13

• Alcohol + Carboxylic acid —> Ester + Water
• (An acid catalyst is used; e.g. concentrated sulfuric acid)
• (Only ester need to know is ethyl ethanoate)