Edexcel International A Level Chemistry Organic Nitrogen Compounds Exam Questions

About Edexcel International A Level Chemistry Organic Nitrogen Compounds

Organic nitrogen compounds in Unit 5 of Edexcel International A Level Chemistry covers amines, amides, amino acids and proteins. You explain the basicity of amines using the nitrogen lone pair, compare aliphatic amines, ammonia and phenylamine, and learn how amines are made from halogenoalkanes and how phenylamine is made by reducing nitrobenzene. Amines react with acids and with acyl chlorides to form amides, and condensation polymerisation gives polyamides such as nylon and Kevlar. Amino acids show both acidic and basic behaviour and form peptides. Examiners test basicity explanations, reaction conditions, drawing repeat units and the structures of amino acids at different pH values.

What you need to know

• Basicity Amines are bases because the nitrogen lone pair accepts a proton. Ethylamine is a stronger base than ammonia because the alkyl group pushes electron density onto N. Phenylamine is weaker because the lone pair is partly delocalised into the benzene ring.
• Preparing amines Aliphatic amines form from halogenoalkanes heated with excess ethanolic ammonia. Phenylamine forms by reducing nitrobenzene with tin and concentrated hydrochloric acid, then adding NaOH to release the free amine.
• Reactions of amines Amines react with acids to form salts, with acyl chlorides to form N-substituted amides, and with halogenoalkanes. With copper(II) ions, they form deep blue complexes, similar to ammonia.
• Polyamides Diamines and dicarboxylic acids (or diacyl chlorides) undergo condensation polymerisation to form polyamides with amide links, such as nylon 6,6 and Kevlar. Water or HCl is eliminated.
• Amino acids Amino acids contain NH2 and COOH groups. In solution they can form zwitterions, H3N+CHRCOO-. In acid the NH2 is protonated; in alkali the COOH loses H+. All except glycine are chiral.
• Peptides and proteins Amino acids join by peptide (amide) links through condensation. Proteins can be hydrolysed back to amino acids by heating with concentrated hydrochloric acid.

Common mistakes in Organic Nitrogen Compounds

• Saying phenylamine is a strong base. It is a weaker base than ammonia because its lone pair is delocalised into the ring.
• Forgetting the NaOH step in making phenylamine. The amine is formed as its salt in acid and must be freed with alkali.
• Drawing a polyamide repeat unit with the amide link reversed or with extra H and OH at the ends.
• Writing the zwitterion with NH2 and COOH unchanged. It is H3N+ and COO-.
• Using an excess of halogenoalkane when trying to make a primary amine. Excess ammonia is needed to reduce further substitution.

Try three Organic Nitrogen Compounds exam-style questions