SIN Startter Quiz - M5L12

The water solubility of carboxylic acids is mainly due to:

• their large hydrocarbon chains

• their nonpolar nature

• their weak acid nature

• their ability to form hydrogen bonds with water

Answer explanation

Carboxylic acids have conditions for formation of hydrogen bonds with water.

Describe a test for a carboxylic acid.

• Add bromine water: the bromine water is decolorised

• Add sodium carbonate:

  effervescence of a gas which turns lime water milky.

• Add 2,4-DNPH: a yellow precipitate is seen

• Add Tollen's reagent: a silver mirror is formed.

Answer explanation

The reaction between sodium carbonate and an acid is used to test for a carboxylic acid.

Select the correct reagents and conditions for the formation of ethyl ethanoate from ethanoic acid and ethanol.

• NaOH and H₂O/ Reflux

• Conc H₂SO₄ as catayst / Reflux

• Bromine water / UV light

• K₂Cr₂O₇ / H⁺ / Reflux

Answer explanation

This is a reversible reaction catalysed by conc H₂SO₄ under reflux

What are the reagents required to form ethanoyl chloride?

• CH₃COOH + SOCl₂

• CH₃COOH + NaCl

• CH₃COOH + HCl

• CH₃COOH + NH₄Cl

Answer explanation

SOCl₂ is required to make ethanoyl chloride from ethanoic acid

Small carboxylic acids are more soluble in water than larger carboxylic acids because:

• they form stronger ionic bonds with water.

• they have a higher molecular weight, which increases solubility.

• they have a smaller hydrophobic hydrocarbon chain, allowing better interaction with water molecules.

• they are less likely to form hydrogen bonds with water.

Answer explanation

The non polar chains predominates over the hydrogen bon formation