SolutionsAcid-Base Properties
1. Order by acidity
Order from most to least acidic: ethanol, 2,2,2-trifluoroethanol, tert-butanol and water.
CF3CH2OH (pKa 12.4) > H2O (15.7) > CH3CH2OH (15.9) > (CH3)3COH (18.0).
Electron-withdrawing groups stabilize the alkoxide; bulky alkyl groups hinder its solvation and destabilize it.
2. Which way does it lie?
State whether these equilibria lie to the right or to the left:
- CH3OH + NaOH ⇌ CH3ONa + H2O
- CH3OH + NaNH2 ⇌ CH3ONa + NH3
- CH3CH2OH + NaH → CH3CH2ONa + H2
- Practically centred (K ≈ 1): methanol (pKa 15.5) and water (15.7) have a similar acidity.
- Far to the right (K ≈ 10^19.5): NH3 (pKa 35) is a much weaker acid than methanol.
- Completely to the right: hydride is a very strong base and H2 is released.
3. Amphoteric
Write the reaction of ethanol with a strong acid and with a strong base. Which species are formed?
With a strong acid: CH3CH2OH + H+ → CH3CH2OH2+ (ethyloxonium ion). With a strong base: CH3CH2OH + B− → CH3CH2O− (ethoxide ion) + BH. The alcohol acts as a base or as an acid depending on the medium.
4. Sodium metal
What happens when sodium metal is added to ethanol?
Sodium ethoxide is formed and hydrogen is released: 2 CH3CH2OH + 2 Na → 2 CH3CH2ONa + H2. This is the usual way of preparing alkoxides in the lab.