Reactions of Carbon Compounds and Everyday Compounds: Quick Revision

A brief note on Reactions of Carbon Compounds and Everyday Compounds. Read it before a test. Try each question at the end before you open its answer.

Four kinds of reaction

Saturated fuels burn with a clean blue flame. Unsaturated fuels, or too little air, give a yellow, sooty flame and carbon monoxide.

Ethanol and ethanoic acid

• Ethanol: mixes with water, neutral to litmus. Sodium gives hydrogen; hot concentrated sulphuric acid gives ethene.
• Ethanoic acid: a weak acid, $5\ \%$ to $8\ \%$ in vinegar. It turns blue litmus red and fizzes with carbonates.
• Esterification: acid $+$ alcohol, with a few drops of concentrated sulphuric acid, gives a sweet-smelling ester and water.

Soaps and detergents

• Soap is the sodium salt of a long-chain carboxylic acid, made by boiling a fat with sodium hydroxide.
• The tails dissolve in grease; the heads stay in the water. Micelles carry the grease away.
• Hard water turns soap into scum. Detergents give no scum.

A worked example

What mass of oxygen burns $75\ \text{g}$ of ethane completely? $2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$.

1. Moles of ethane. $75\ \text{g} \div 30\ \text{g/mol} = 2.5\ \text{mol}$.
2. Moles of oxygen. $\dfrac{7}{2} \times 2.5 = 8.75\ \text{mol}$.
3. Mass of oxygen. $8.75 \times 32 = 280\ \text{g}$.

Practice with new numbers

A program to try

The program works out the worked example, with the products too.

Mistakes to avoid

• Adding hydrogen to an alkane. Alkanes are saturated; they react by substitution.
• Calling ethanoic acid not an acid because it is weak. Weak means few hydrogen ions, not none.
• Mixing up an ester and a salt. An acid and an alcohol give an ester; an acid and a base give a salt.
• Blaming the water for scum. It is the calcium and magnesium ions that turn soap into scum.

Check yourself

1. What flame does a saturated hydrocarbon give in plenty of air?

2. Why is hydrogenation useful to food makers?

3. Why does a soap micelle hold grease?

4. How does ethanoic acid smell?