November 2019

Codeine, morphine and diamorphine (heroin) are derived from opium. (a) Explain why diamorphine has greater potency than morphine. [3]

Conversion of 2 hydroxyl groups of morphine to ester in diamorphine. This makes diamorphine less polar than morphine. Hence, diamorphine is more hydrophobic making it cross blood-brain barrier more easily.

(d) Discuss two difficulties, apart from socio-economic factors, associated with finding a cure for AIDS. [2]

HIV mutates rapidly/quickly ✔ HIV attacks immune system ✔

Body fluids have different pH values. (a) Identify the compound responsible for the acidity of gastric juice, and state whether it is a strong or weak acid. [1]

Hydrochloric acid and strong acid

(b) Outline how ranitidine reduces stomach acidity. [1]

Prevents parietal cells from releasing acid by blocking H2-histamine receptors.

(b) Experimental research on both animals and humans contributes to the development of pharmaceuticals. State the meaning of the term therapeutic index in human studies. [1]

TD50/ED50

The discovery of penicillins contributed to the development of antibiotics. (a) Explain how the beta-lactam ring is responsible for the antibiotic properties of penicillin. Refer to section 37 of the data booklet. [3]

angles of 90° instead of 109.5/109/120° angles ✔ ring reacts «easily» ✔ inhibits enzyme/transpeptidase «in bacteria» that produces cell walls ✔

Steroids are lipids with a steroidal backbone. The structure of cholesterol is shown in section 34 of the data booklet. (a) Infrared (IR) spectroscopy is used to identify functional groups in organic compounds. Deduce the wavenumber, in cm −1, of an absorption peak found in the IR spectrum of testosterone but not in that of cholesterol. [1]

1700−1750 «cm−1» ✔

(c) Suggest a concern about the disposal of solvents from drug manufacturing. [1]

carcinogenic/can cause cancer ✔

(b) Describe how the challenge in (a) was resolved by pharmaceutical companies. [1]

chiral auxiliaries binds to reactant blocking one reaction site

(b) Aspirin, C6H4(OCOCH3)COOH, is only slightly soluble in water. Outline, including an equation, how aspirin can be made more water-soluble. Use section 37 in the data booklet. [2]

convert to «ionic» salt ✔ C6H4(OCOCH3)COOH (s) + NaOH (aq) --> C6H4(OCOCH3)COONa (aq) + H2O (l) ✔

The structure of aspirin is shown in section 37 of the data booklet. (a)Suggest one reactant used to prepare aspirin from salicylic acid. [1]

ethanoic acid

Nuclear medicine uses small amounts of radioisotopes to diagnose and treat some diseases. (a) State two common side effects of radiotherapy. [1]

hair loss loss of weight

(b) Explain why technetium-99m is the most common radioisotope used in nuclear medicine. [2]

half-life is 6 hours/long enough for a scan to occur and half-life short enough not to remain in body ✔ decay releases «low energy» gamma rays and gamma rays less likely to be absorbed by cells ✔

(b) Outline the impact of antibiotic waste on the environment. [1]

leads to antibiotic resistance

(c) 25.0 μg of iodine-131, with a half-life of 8.00 days, was left to decay. Calculate the mass of iodine-131, in μg, remaining after 32.0 days. Use section 1 of the data booklet.[2]

m=25.0(1/2)^32.0/8 = 1.56 ug ✔

Taxol is an anticancer drug. (a) State the feature of Taxol that is a major challenge in its synthesis. Use section 37 of the data booklet. [1]

numerous chiral carbons/ optical isomers

(c) Explain how redox chemistry is used to measure the ethanol concentration in a breathalyser. [2]

oxidizing agent/«acidified» potassium dichromate(VI) converts ethanol to ethanoic acid ✔ colour change «from orange to green» is measured/analysed «using photocell» ✔

(c) Calculate the pH of a buffer solution which contains 0.20 mol dm−3 ethanoic acid and 0.50moldm−3 sodium ethanoate. Use section 1 of the data booklet. [1] pKa (ethanoic acid) = 4.76

pKa = 4.76 pH = pKa + log(CH3COO-/CH3COOH) pH = 4.76 + 0.40 = 5.16 ✔

(b) Describe a technique for the detection of steroids in blood and urine. [3]

sample carried by inert gas «through column» ✔ packing/solid support acts as stationary phase ✔ gases/liquids/components move through tube/column at different speeds/rates ✔ databases/library of known fragmentation patterns can be used ✔