CbD - Organic reactions

Question 1

What 7 types can organic chemistry reactions be classified into?

Answer 1

addition
elimination
substitution
condensation
hydrolysis
oxidation
reduction

Question 2

Addition

Answer 2

2 molecules join together to form a single product. Involves breaking a double bond.

Question 3

Elimination

Answer 3

Involves removing a functional group which is released as a part of a small molecule. Often a double bond is formed.

Question 4

Substitution

Answer 4

A functional group on a molecule is swapped for a new one.

Question 5

Condensation

Answer 5

2 molecules get joined together with the loss of a small molecule, e.g. water. The opposite of hydrolysis.

Question 6

Hydrolysis

Answer 6

Water is used to split apart a molecule creating two smaller ones. Opposite of condensation.

Question 7

Oxidation

Answer 7

Oxidation is loss of electrons. In organic chemistry it usually means gaining an oxygen atom or losing a hydrogen atom.

Question 8

Reduction

Answer 8

Reduction is gain of electrons. In organic chemistry it usually means gaining a hydrogen atom or losing an oxygen atom.

Question 9

What does bromine water test for?

Answer 9

Alkenes

Question 10

What is used to test for alkenes?

Answer 10

Bromine water

Question 11

What are you actually testing for when testing whether something is an alkene using bromine water?

Answer 11

The presence of double bonds.

Question 12

Explain how bromine water is used to test for alkenes

Answer 12

1) Add 2cm3 of the solution that you want to test to a test tube.
2) Add 2cm3 of bromine water to the test tube.
3) Shake the test tube.

Alkene = the solution will decolourise (go from orange to colourless).
Not alkene = nothing happens.

Question 13

What colour is bromine water?

Answer 13

Orange

Question 14

Positive test with bromine water

Answer 14

Alkene = the solution will decolourise (go from orange to colourless).

Question 15

Explain how you test whether an alcohol is a primary, secondary or tertiary alcohol?

Answer 15

1) Add 10 drops of the alcohol to 2cm3 of acidified potassium dichromate solution in a test tube.
2) Warm the mixture gently in a hot water bath.
3) Then watch for a colour change.

Primary = the orange solution slowly turns green as an aldehyde forms. (If you carry on heating, the aldehyde will be oxidised further to give a carboxylic acid.)

Secondary = the orange solution slowly turns green as a ketone forms.

Tertiary = nothing happens.

Question 16

What happens when you mix acidified potassium dichromate(VI) solution with a primary alcohol?

Answer 16

Primary = the orange solution slowly turns green as an aldehyde forms. (If you carry on heating, the aldehyde will be oxidised further to give a carboxylic acid.)

Question 17

What happens when you mix acidified potassium dichromate(VI) solution with a secondary alcohol?

Answer 17

Secondary = the orange solution slowly turns green as a ketone forms.

Question 18

What happens when you mix acidified potassium dichromate(VI) solution with a tertiary alcohol?

Answer 18

Tertiary = nothing happens.

Question 19

What causes the colour change when alcohols (primary and secondary) are mixed with acidified potassium dichromate(VI) solution?

Answer 19

The colour change is the orange dichromate(VI) ions (Cr2O7^2-) being reduced to the green chromium(III) ion (Cr^3+).

Question 20

What is the downside to testing for which sort of alcohol you have using acidified potassium dichromate(VI) solution?

Answer 20

The result for primary and secondary alcohol is the same.

Question 21

How do you test whether something is a primary or secondary alcohol?

Answer 21

1) Add excess alcohol to 2cm3 of acidified potassium dichromate(VI) solution in a round bottomed flask.
2) Set up the flask as part of distillation apparatus.
3) Gently heat the flask. The alcohol will be oxidised and the product will be distilled off immediately so you can collect it.
4) Once you have collected the product, you need to test it to find out if it is an aldehyde or a ketone using Tollens reagent or Fehling’s solution. If it is an aldehyde, you started with a primary alcohol. If it is a ketone, you started with a secondary alcohol.

Question 22

What do you use to oxidise alcohols?

Answer 22

Acidified potassium dichromate(VI).