1. a)
i) To calculate the empirical formula of A, we assume 100 g of the compound. Therefore, the mass of each element in the compound is:
Carbon = 60.0 g
Hydrogen = 13.3 g
Oxygen = 26.7 g
We can then convert these masses to moles by dividing by their respective atomic masses:
Carbon: 60.0 g / 12.0 g/mol = 5.0 mol
Hydrogen: 13.3 g / 1.0 g/mol = 13.3 mol
Oxygen: 26.7 g / 16.0 g/mol = 1.67 mol
We divide each of these moles by the smallest number of moles, which is 1.67, to get the simplest whole-number ratio:
Carbon: 5.0 mol / 1.67 mol = 2.99 ≈ 3
Hydrogen: 13.3 mol / 1.67 mol = 7.96 ≈ 8
Oxygen: 1.67 mol / 1.67 mol = 1
Therefore, the empirical formula of A is C3H8O.
ii) The molecular mass of A is 60, which is equal to the empirical formula mass. Therefore, the molecular formula is the same as the empirical formula: C3H8O.
b) There are two isomers of A: propanol-1 (1-propanol) and propanol-2 (2-propanol).
c) A is propanol-2 (2-propanol). When heated with a mixture of sulfuric acid and potassium dichromate(VI), propan-2-one is formed via oxidation of the alcohol functional group.
d)
i) When heated with pumice or concentrated sulfuric acid, A undergoes dehydration to form propene (propylene):
CH3CH(OH)CH2OH → CH3CH=CH2 + H2O
ii) When reacted with ethanoic acid in the presence of an acid catalyst, A undergoes esterification to form propyl ethanoate:
CH3CH(OH)CH2OH + CH3COOH → CH3COOCH2CH2CH3 + H2O
2. a)
There are four isomers of C4H10O:
- Butan-1-ol (1-butanol)
- Butan-2-ol (2-butanol)
- 2-methylpropan-1-ol (isobutanol)
- 2-methylpropan-2-ol (tert-butanol)
b)
i) B is butan-2-ol (2-butanol). When heated with a mixture of sulfuric acid and potassium dichromate(VI), there is no change in colour because butan-2-ol cannot be oxidized by the dichromate ion.
ii) The alkene formed when butan-2-ol is dehydrated is but-1-ene (1-butene):
CH3CH(OH)CH2CH3 → CH2=CHCH2CH3 + H2O
c)
i) C is butan-1-ol (1-butanol).
ii) When refluxed with an excess of acidified potassium dichromate(VI) mixture, C is oxidized to butanone (methyl ethyl ketone):
CH3CH2CH2CH2OH + [O] → CH3C(O)CH2CH3 + H2O
iii) Reflux is a process in which a reaction mixture is heated to boiling and the vapours are condensed and returned to the reaction vessel. This ensures that the reaction proceeds to completion and that no volatile components are lost.
3. a)
i) To calculate the empirical formula of D, we assume 100 g of the compound. Therefore, the mass of each element in the compound is:
Carbon = 53.3 g
Hydrogen = 11.1 g
Oxygen = 35.6 g
We can then convert these masses to moles by dividing by their respective atomic masses:
Carbon: 53.3 g / 12.0 g/mol = 4.44 mol
Hydrogen: 11.1 g / 1.0 g/mol = 11.1 mol
Oxygen: 35.6 g / 16.0 g/mol = 2.23 mol
We divide each of these moles by the smallest number of moles, which is 2.23, to get the simplest whole-number ratio:
Carbon: 4.44 mol / 2.23 mol = 1.99 ≈ 2
Hydrogen: 11.1 mol / 2.23 mol = 4.98 ≈ 5
Oxygen: 2.23 mol / 2.23 mol = 1
Therefore, the empirical formula of D is C2H5O.
ii) The relative molecular mass of D is 90. The empirical formula mass of C2H5O is 45 (2 x 12.0 + 5 x 1.0 + 16.0 = 45). Therefore, the molecular formula of D is twice the empirical formula: C4H10O2.
b) A diol is a molecule that contains two hydroxyl (-OH) functional groups. Therefore, D is a diol.