Ethanol and ethanoic acid

Ethanol

Ethanol, $\text{C}_2\text{H}_5\text{OH}$, is a colourless liquid. It boils at $351\ \text{K}$ and mixes with water in any ratio. It is neutral to litmus. It is in alcoholic drinks. It is a good solvent, and it is used in medicines, tinctures, cough syrups and perfumes.

With sodium. Ethanol reacts with sodium metal. Bubbles of hydrogen come out.

The product is sodium ethoxide. The test shows the –OH group.

Dehydration. Heated at $443\ \text{K}$ with concentrated sulphuric acid, ethanol loses a water molecule and becomes ethene. The acid takes the water out.

Effects of alcohol on the body

Ethanol in drinks affects the nervous system. It slows the reaction time and can cause loss of control. Large amounts can harm the liver and cause death. Methanol is far worse. In the body, the liver changes it to methanal. This damages the nerve of the eye and can cause blindness or death. To stop the misuse of the cheap industrial ethanol, a poison such as methanol and a dye are added to make it denatured alcohol.

Ethanoic acid

Ethanoic acid (acetic acid), $\text{CH}_3\text{COOH}$, is a carboxylic acid. A solution of $5\ \%$ to $8\ \%$ in water is vinegar, which is used to preserve pickles. Pure ethanoic acid freezes at $290\ \text{K}$ ($17\ ^{\circ}\text{C}$) and is called glacial ethanoic acid, because it turns into ice-like crystals on a cold day.

It is a weak acid: it gives only a few hydrogen ions, so its pH is higher than that of hydrochloric acid of the same concentration. But it behaves as an acid.

• With a base: $\text{CH}_3\text{COOH} + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O}$. The salt is sodium ethanoate.
• With a carbonate: $2\,\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \rightarrow 2\,\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2$. The gas turns limewater milky.

Esterification

Ethanoic acid reacts with ethanol, with a few drops of concentrated sulphuric acid as a catalyst, to make an ester and water.

The ester here is ethyl ethanoate. It has a sweet, fruity smell. Esters are used in perfumes and as flavours in food.

When an ester reacts with a base, such as sodium hydroxide, it gives back the alcohol and the sodium salt of the acid. This is the reaction that makes soap, which is why it is called saponification.

You should find that the smaller bar, not the smaller mass, decides how much ester forms.

Practise with new numbers

Try it in Python

This program finds the mass of the ester that is made from ethanoic acid and ethanol, and the percentage yield.

Remember these

• Ethanol: mixes with water, neutral. With sodium it gives hydrogen. With conc. $\text{H}_2\text{SO}_4$ at $443\ \text{K}$ it gives ethene.
• Ethanoic acid: a weak acid, $5\ \%$ to $8\ \%$ in vinegar. It reacts with bases and carbonates.
• Acid + alcohol, with a catalyst, gives an ester with a sweet smell, and water.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Why is ethanol used in cough syrups and tinctures?

2. Ethanoic acid is called a weak acid. What does weak mean here?

3. Ethanoic acid reacts with sodium hydroxide. Name the salt that forms.

4. What job does the concentrated sulphuric acid do in esterification?