Quick answer: Amines are organic bases because the lone pair on nitrogen accepts a proton, and amino acids contain both an amine and an acid group so they form zwitterions. This Chemistry 11-12 test on amines and polymers has 8 questions worth 20 marks, to do in 45 minutes: basic strength, pH of dimethylamine and serine melting point. The mark scheme is on a separate page; free printable PDF.
This test covers amine basicity, amino acids, condensation polymers and DNA. Calculators are allowed, so show working for every calculation. Also, the marks appear beside each part.
Level: Chemistry grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.3.11-3.3.13
Question 1 Basic strength (3 marks)
Ethylamine has pKb 3.35 and phenylamine has pKb 9.13.- Firstly, state which is the stronger base. (1 mark)
- Then explain the difference in terms of the nitrogen lone pair. (2 marks)
Question 2 pH of dimethylamine (3 marks)
Calculate the pH at 25 °C of 0.0400 mol/dm³ dimethylamine, Kb = 5.4 × 10⁻⁴ mol/dm³, with Kw = 1.0 × 10⁻¹⁴. (3 marks)Question 3 Serine melting point (2 marks)
Serine, HOCH₂CH(NH₂)COOH, melts above 200 °C with decomposition, much higher than a carboxylic acid of similar Mr.- Firstly, draw the structure present in the solid. (1 mark)
- Then explain the high melting point. (1 mark)
Question 4 Poly(lactic acid) (3 marks)
Lactic acid is CH₃CH(OH)COOH, so it forms poly(lactic acid), PLA.- Firstly, name the link and the small molecule lost. (1 mark)
- Then calculate the Mr of the repeat unit and of a chain of 450 units (C = 12.0, H = 1.0, O = 16.0). (2 marks)
Question 5 Tripeptide (3 marks)
The diagram shows a tripeptide.- Firstly, name the links X and Y. (1 mark)
- Then calculate the Mr of the tripeptide. (2 marks)
Question 6 Nylon or polypropene (2 marks)
Explain why boiling aqueous hydrochloric acid breaks down nylon-6,6 but not poly(propene). (2 marks)Question 7 Hydrogen bonds in DNA (2 marks)
A DNA fragment has 40 base pairs and 15 of its 80 nucleotides are adenine. Then calculate the total number of hydrogen bonds between the strands. (2 marks)Question 8 Choosing the reagent (2 marks)
You make propylamine from 1-bromopropane. Name the reagent and a suitable condition, and explain why a mixture forms if the reagent is limited. (2 marks)
