Pharmaceutical Chemistry Questions and Answers

Answer: A

Penicillin V is phenoxymethylpenicillin.

The phenoxymethyl side chain makes it stable in gastric acid, which is why penicillin V is the penicillin given by mouth.

The other three are forms of penicillin G (benzylpenicillin), which acid destroys and which is therefore injected. Benzylpenicillin sodium is the soluble salt for intravenous or intramuscular use. Benzathine penicillin and procaine penicillin are poorly soluble depot salts given intramuscularly so that penicillin G is released slowly over days (benzathine) or about a day (procaine).

Answer: A

ORS belongs to the group of electrolytes and carbohydrates.

The WHO low-osmolarity formula contains sodium chloride, potassium chloride and trisodium citrate (electrolytes) with anhydrous glucose (a carbohydrate). The glucose matters: sodium and glucose are absorbed together across the intestinal wall, and water follows, which is why ORS rehydrates even during diarrhoea.

ORS contains no proteins or enzymes, no vitamins, and no lipids or amino acids, so the other groupings do not describe it.

Answer: A

The answer is Salicylic Acid.

Strictly, aspirin is acetylsalicylic acid, the acetyl ester of salicylic acid, made by acetylating salicylic acid with acetic anhydride. Chemically it belongs to the salicylic acid derivatives (salicylates), and that is the classification the key accepts: salicylic acid is the only option that is aspirin's parent compound.

The other options are the parent acids of other NSAID groups. Indole acetic acid is the parent of indomethacin, propionic acid of ibuprofen and naproxen, and anthranilic acid of the fenamates such as mefenamic acid.

Answer: A

The isotope is I-131 (iodine-131).

The thyroid takes up iodine to make its hormones, so radioactive iodine concentrates there. Small doses are used to measure thyroid uptake in thyroid disorders, and larger doses destroy thyroid tissue in hyperthyroidism and thyroid cancer, which makes I-131 both diagnostic and therapeutic.

The others are used elsewhere: chromium-51 labels red cells to measure their survival and volume, iron-59 traces iron metabolism, and cobalt-57 labels vitamin B12 in the Schilling test for its absorption.

Answer: B

Clark's process is used to remove temporary hardness of water by adding slaked lime.

Temporary hardness is caused by calcium and magnesium bicarbonates. A calculated quantity of slaked lime converts the soluble bicarbonate into insoluble calcium carbonate, which settles out:

Ca(HCO₃)₂ + Ca(OH)₂ → 2CaCO₃ + 2H₂O

Permanent hardness, caused by sulphates and chlorides, is not removed by lime alone; it needs washing soda or ion exchange. Lime is not used here as a disinfectant, and the process makes water less acidic, not more.

Answer: B

The formula of calcium gluconate is \(\text{C}_{12}\text{H}_{22}\text{CaO}_{14}\).

Gluconic acid is \(\text{C}_6\text{H}_{12}\text{O}_7\). Losing one hydrogen gives the gluconate ion, \(\text{C}_6\text{H}_{11}\text{O}_7^{-}\). Calcium is divalent, so it combines with two of them:

\[ \begin{aligned} &\text{Ca}(\text{C}_6\text{H}_{11}\text{O}_7)_2 \\ &= \text{C}_{12}\text{H}_{22}\text{CaO}_{14} \end{aligned} \]

\(\text{CaCl}_2\) is calcium chloride and \(\text{CaCO}_3\) is calcium carbonate, other calcium salts. \(\text{C}_6\text{H}_5\text{O}_7\) is the citrate ion, and calcium citrate is \(\text{Ca}_3(\text{C}_6\text{H}_5\text{O}_7)_2\), so the first option is not gluconate either.

Answer: B

The radiopharmaceutical is indium chloride.

Indium chloride labelled with the short-lived isotope indium-113m is listed among radiopharmaceuticals for localising the placenta and for imaging the cardiac blood pool. Injected, it binds to transferrin in the plasma and stays within the blood, so it outlines large pools of blood such as the placenta and the heart chambers.

The other three are ordinary inorganic preparations, not radioactive diagnostics: ammonium bromide is a sedative salt, calcium chloride solution is a calcium supplement, and ferric chloride solution is an astringent and laboratory reagent.

Answer: B

Ammonium chloride is used as an expectorant.

Taken by mouth it irritates the gastric mucosa slightly, and this reflexly increases the flow of thin bronchial secretions, so phlegm is easier to cough up. It is a common ingredient of cough syrups. It is also used as a systemic and urinary acidifier.

It has no antiseptic, analgesic or antipyretic action worth using, so the other options do not describe it.

Answer: C

Macrolide antibiotics contain a lactone ring.

The name 'macrolide' means a large (macro) cyclic lactone. Erythromycin, clarithromycin and azithromycin have a 14- to 16-membered macrocyclic lactone ring with one or more sugars attached. They inhibit bacterial protein synthesis at the 50S ribosome.

A lactam ring is the feature of the beta-lactams (penicillins and cephalosporins). A phenanthrene nucleus is found in steroids and in morphine. A naphthalene nucleus is not part of the macrolide structure; the tetracyclines, for example, are built on a four-ring naphthacene system.

Answer: C

The ring system the key accepts is pyrimidine.

Methotrexate contains a pteridine nucleus (2,4-diaminopteridine) joined through p-aminobenzoic acid to glutamic acid. Pteridine is a fused bicyclic system of a pyrimidine ring and a pyrazine ring, so of the options given, pyrimidine is the ring present.

Purine, which is pyrimidine fused with imidazole, is the nucleus of 6-mercaptopurine and the other purine antagonists, not of methotrexate. Pyridine has a single nitrogen, and imidazole is a five-membered ring; neither is in methotrexate's nucleus.