Topic 6E - Alcohols (Organic Chemistry)

Question 1

What is a primary alcohol?

Answer 1

When there is an -OH functional group on a carbon attached only one other carbon

Question 2

What is a secondary alcohol?

Answer 2

When there is an -OH functional group on a carbon which is attached to two other carbons

Question 3

What is a tertiary alcohol?

Answer 3

When there is an -OH functional group on a carbon which is attached to three other carbons

Question 4

What is the name of the primary, secondary and tertiary alcohol C4H9OH?

Answer 4

Primary - Butan-1-ol
Secondary - Butan-2-ol
Tertiary - Methylpropan-1-ol

Question 5

Why are the boiling temperatures of alcohols higher than their corresponding alkanes?

Answer 5

Due to the addition of Hydrogen Bonding

Question 6

Why is ethanol very water soluble?

Answer 6

Due to the ability of ethanol to form hydrogen bonds between the -OH and the water molecule

Question 7

The solubility of alcohols decreases with…

Answer 7

Increasing carbon chain length

Question 8

Why does solubility decrease with increasing carbon chain length?

Answer 8

This is because the large, insoluble hydrocarbon portion of the molecule outweighs the influence of the -OH group

Question 9

Write the word equation and balanced symbol equation for the combustion of methanol

Answer 9

methanol (l) + oxygen (g) -> Carbon dioxide (g) + water (l)

2CH3OH + 3O2 -> 2CO2 + 4H2O

Question 10

Write the word and symbol equation of the reaction of sodium with ethanol

Answer 10

Sodium + Ethanol -> Sodium ethoxide + Hydrogen

Na + CH3CH2OH -> CH3CH2O-Na+ + 1/2H

Question 11

What is a way to safely dispose a small amount of unwanted sodium?

Answer 11

To react the sodium with ethanol

Question 12

What is the name of reaction where the -OH functional group is swapped for a halogen?

Answer 12

A substitution reaction

Question 13

In the Chlorination of primary and secondary alcohols what is the reagent?

Answer 13

PCl5 (Phosphorus Pentachloride)

Question 14

In the Chlorination of primary and secondary alcohols what are the conditions?

Answer 14

No heating is required but the reaction should be done in a fume cupboard as HCl gas is produced which is toxic

Question 15

Write a word and symbol equation for reaction of the primary alcohol ethanol and PCl5 in Chlorination

Answer 15

Ethanol + Phosphorus Pentachloride -> Chloroethane + Phosphorus oxychloride + Hydrogen Chloride

CH3CH2OH + PCl5 -> CH3CH2Cl + POCl3 + HCl

Question 16

What is the reaction used to test for the presence of the -OH functional group in primary and secondary alcohols?

Answer 16

Chlorination

Question 17

What is the positive result of the present of the -OH functional group, when testing for it with PCl5?

Answer 17

Clouds of misty fumes due to the HCl gas, these will turn damp blue litmus paper red

Question 18

In the Chlorination of tertiary alcohols what is the reagent?

Answer 18

Shaken with Concentrated HCl

Question 19

In the Chlorination of tertiary alcohols what are the conditions?

Answer 19

Room Temperature

Question 20

Write a symbol equation for the reaction of the tertiary alcohol tert-butyl alcohol with HCl in Chlorination

Answer 20

(CH3)3COH + HCl -> (CH3)3CCl + H2O

Question 21

In the Bromination of alcohols, what are the reagents?

Answer 21

• Solid KBr
• H2SO4 with a 50% concentration

Question 22

In the Bromination of alcohols what are the conditions?

Answer 22

Heat under reflux (2nd step)

Question 23

What are the 2 different equations for the first step of the Bromination of Alcohols?

Answer 23

KBr (s)+ H2SO4 (aq) -> KHSO4 (aq) + HBr (g)

2KBr (s) + H2SO4 (aq) -> K2SO4 (aq) + 2HBr (g)

Question 24

Write the general equation (using ethanol) for the second step of the Bromination of alcohols

Answer 24

CH3CH2OH + HBr -> CH3CH2Br + H2O

Question 25

Why is it important to use 50% concentrated sulphuric acid rather than fully concentrated acid?

Answer 25

As using a fully concentrated acid would cause all of the Br- ions to be oxidised to Br2 rather than Her which is what is needed

Question 26

Write an equation for the first step in the Iodination of alcohols

Answer 26

2P + 3I2 -> 2PI3

Question 27

What are the reactants and conditions in the first step of the Iodination of alcohols?

Answer 27

Reactants: - Damp red phosphorus - Iodine Conditions - Warmed

Question 28

Write an equation for the second step of the Iodination of alcohols using ethanol

Answer 28

3CH3CH2OH + PI3 -> 3CH3CH2I +H3PO3 (phosphonic acid)

Question 29

What are the conditions required for the second step of the Iodination reaction with alcohols?

Answer 29

Heat under reflux

Question 30

What is the definition of a dehydration reaction?

Answer 30

A dehydration reaction is a specific type of elimination reaction where water is removed form a saturated molecule to form an unsaturated molecule

Question 31

What is the definition of an elimination reaction?

Answer 31

An elimination reaction is when two atoms or a group of atom are removed from a compound to form two products

Question 32

What is the general equation for the dehydration of an alcohol?

Answer 32

Alcohol -> Alkene + water

Question 33

What are the conditions required for the dehydration of an alcohol?

Answer 33

- Heat under reflux - Phosphoric acid catalyst (H3PO4) - Collect the product via distillation

Question 34

What is the oxidised dichromate (VI) ion?

Answer 34

Cr2O7 (2-)

Question 35

What is the reduced dichromate ion?

Answer 35

Cr (3+)

Question 36

What is the colour change you observe as the dichromate ion is reduced?

Answer 36

Orange to Green

Question 37

What are the conditions for the oxidation of primary alcohols?

Answer 37

- Heat under reflux

Question 38

What is the oxidising agent/reagants required from the oxidation of primary alcohols?

Answer 38

- Potassium Dichromate - Sulphuric acid

Question 39

Write an equation for the partial oxidation of the primary alcohol propan-1-ol to an aldehyde

Answer 39

propan-1-ol -> propanal + water CH3CH2CH2OH + [O] -> CH£CH2CHO + H2O

Question 40

How would you collect the partially oxidised aldehyde product?

Answer 40

Distill off immediately

Question 41

Write the equation of the oxidation of the aldehyde propanal to a carboxylic acid

Answer 41

propanal -> propanoic acid CH3CH2CHO + [O] -> CH3CH2COOH

Question 42

Write the full equation for when button-1-ol is completely oxidised to butanoic acid

Answer 42

CH3CH2CH2CH2OH +2[O] -> CH3CH2CH2COOH + H2O

Question 43

What is the oxidising agent/reagants required from the oxidation of secondary alcohols?

Answer 43

- Potassium Dichromate - Sulphuric acid

Question 44

What are the conditions for the oxidation of secondary alcohols?

Answer 44

- Heat under reflux

Question 45

Write the equation for the complete oxidation of propan-2-ol?

Answer 45

CH3CHOHCH3 + [O] -> CH3COCH3 + H2O

Question 46

How can you show that the oxidation product from secondary alcohols has been oxidised but not to a carboxylic acid?

Answer 46

The colour change from orange to green due to the reduction of the dichromate ion shows that the alcohol is being oxidised. Test for the presence of a Carboxylic Acid functional group - Add Na2CO3 to your product. Bubble the effervescence through limewater and if CO2 is present the limewater should turn cloudy. Therefore a carboxylic acid would be present, or not. NB - Carboxylic Acid + Metal Carbonate -> Salt + Carbon Dioxide + Water

Question 47

How could you test to se if an organic product is an aldehyde rather than a ketone or carboxylic acid?

Answer 47

Aldehydes are only partially oxidised, therefore if you were to heat it under reflux in the presence of H2SO4 and Potassium dichromate there would be a colour change of orange to green.

Question 48

What is a test that you can use to distinguish between an aldehyde and a ketone?

Answer 48

Fehlings/Benedicts test

Question 49

Describe how to test for the presence of an aldehyde using the Fehlings/Benedicts test?

Answer 49

Add a few drops of the aldehyde to the reagent and then warm gently in a hot water bath for a few minutes

Question 50

What is the positive colour change for a Fehlings/Benedicts test?

Answer 50

The blue solution produces a dark red precipitate of copper (I) oxide (aldehydes)

Question 51

What are the three reasons why it is unlikely that your product of any reaction in organic chemistry to be pure?

Answer 51

- You often add excess of one reagent and so there will be unreacted starting material - There are often extra reactions during the one that you are doing, particularly inorganic ones - Water has been formed during the reaction or your solvent from the reaction

Question 52

Why do you need anti - bumping granules when heating an alcohol?

Answer 52

To prevent the formation of large gas bubbles that cause violent boiling by providing a large surface area for bubbles to form on

Question 53

What must you not do when distilling a solution?

Answer 53

Let the flask boil dry as otherwise there could be an explosion

Question 54

What are the observations when sodium reacts with alcohols?

Answer 54

The reaction is similar to when sodium is reacted with water. However, this reaction is: - Much less violent - Not as exothermic The hydrogen gas is still produced but the sodium does not melt.

Question 55

What is produced when sodium reacts with alcohols?

Answer 55

Sodium alkoxide salts and hydrogen are produced. The salts are ionic and this is shown by including the charges of - on the oxygen o the alkoxide ion and the + of the sodium ion.

Question 56

What two organic products can be formed when butan-2-ol is dehydrated?

Answer 56

but-1-ene or but-2-ene

Question 57

What is the condition required for the dichromate ion to function as an oxidising agent?

Answer 57

The presence of H+ ions, therefore sulphuric acid is used to provide these