CCEA A Level Chemistry 5.11 Chemistry in Medicine Exam Questions

About CCEA A Level Chemistry 5.11 Chemistry in Medicine

Section 5.11 is the applied chemistry section at the end of Unit A2 2. It brings together ideas from across the course in a medical context. You need antacids such as hydroxides and carbonates and the back titration of an indigestion remedy, cisplatin and how its structure lets it stop DNA replication in cancer cells, and the preparation of aspirin from salicylic acid and ethanoic anhydride with its volumetric analysis. CCEA also asks how TLC and GLC-MS identify drugs and check purity, how carbon monoxide affects iron(II) in haemoglobin, and how edta sequesters calcium ions to prevent blood clotting. Expect questions that combine calculations with transition metal and organic chemistry.

What you need to know

• Antacids Excess stomach acid is neutralised by bases such as magnesium hydroxide, aluminium hydroxide and calcium carbonate, for example Mg(OH)2 + 2HCl gives MgCl2 + 2H2O. The amount of base is found by back titration: dissolve in excess acid, then titrate the leftover acid with standard alkali.
• Cisplatin Cisplatin, [Pt(NH3)2Cl2], is square planar with the two chloride ligands next to each other (cis). The chlorides are replaced by nitrogen atoms on DNA bases, which stops DNA replication in cancer cells. The trans isomer cannot bind in the same way and is ineffective.
• Aspirin Salicylic acid (2-hydroxybenzoic acid) reacts with ethanoic anhydride to give aspirin (2-ethanoyloxybenzoic acid) and ethanoic acid. The crude product is recrystallised and its purity checked by melting point or TLC. The sodium salt is more soluble.
• Drug analysis Aspirin content is found by titration. TLC compares spots with pure standards; GLC-MS separates components and identifies each one from its mass spectrum.
• Haemoglobin and CO Haemoglobin contains an iron(II) complex that binds oxygen as a ligand. Carbon monoxide binds more strongly than oxygen and is not easily released, reducing oxygen transport.
• Edta Edta forms a stable hexadentate complex with Ca2+ ions, removing them from solution. Calcium ions are needed for clotting, so edta is used to stop stored blood clotting.

Common mistakes in 5.11 Chemistry in Medicine

• Saying the trans isomer of cisplatin is the active drug. Only the cis isomer binds to DNA effectively.
• Saying CO poisons by reacting with oxygen in the blood. It binds to the iron(II) in haemoglobin in place of oxygen.
• In antacid back titrations, using the alkali moles as the moles of antacid. Find the acid that reacted first, then use the ratio.
• Giving cisplatin as tetrahedral. Platinum(II) complexes like cisplatin are square planar.
• Forgetting the second product in aspirin synthesis. Ethanoic anhydride gives aspirin and ethanoic acid.

Try three 5.11 Chemistry in Medicine exam-style questions