NDA (II) 2022 General Ability Test · Question 105 of 150

Correct — D, methanoic acid. Methanoic acid is the IUPAC name for formic acid, HCOOH, the simplest carboxylic acid and the one school chemistry attributes to the sting of bees and ants. The older name comes from formica, the Latin word for ant. Because the irritant is an acid, the standard first-aid line in the textbook is to rub on a mild base such as baking soda, which neutralises it and relieves the pain.

• (a)tartaric acid — Tartaric acid is the acid of tamarind and grapes, and is one component of baking powder. No insect injects it.
• (b)citric acid — Citric acid is the acid of citrus fruits such as lemon, orange and lime, and gives them their sour taste. It has nothing to do with a sting.
• (c)ethanoic acid — Ethanoic acid is the modern name for acetic acid, the acid of vinegar, which is a dilute aqueous solution of it. It is the next member up the same series from methanoic acid, which makes it the most tempting wrong answer in the set.

Carboxylic acids form a homologous series built on the -COOH group. The first member is methanoic acid, HCOOH, historically called formic acid; the second is ethanoic acid, CH₃COOH, historically called acetic acid. Both are weak acids that only partially ionise in water, which is why a sting stings and burns but does not destroy tissue the way a mineral acid would.

The question is really checking whether the old and new names have been learned as pairs — formic with methanoic, acetic with ethanoic. Once that mapping is fixed, the ant-and-bee association picks out option (d) immediately. It is worth being honest about the underlying biology, because the syllabus keeps a simplification here. Honey-bee venom is not a vial of formic acid but a protein mixture in which the peptide melittin makes up about 52 per cent of the venom peptides, alongside phospholipase A2, apamin, hyaluronidase and histamine. Formic acid is the classic irritant of the venom of formicine ants, and textbooks extend the same explanation to the bee. Answer to the textbook chemistry in the exam; carry the fuller picture for the laboratory.

• Methanoic acid is the IUPAC name for formic acid, HCOOH, the first member of the carboxylic acid series.
• Ethanoic acid, CH₃COOH, is acetic acid, the acid present in vinegar.
• Citric acid occurs in citrus fruits and tartaric acid in tamarind and grapes.
• A sting is acidic, so rubbing on a mild base such as baking soda relieves the irritation.
• Honey-bee venom is chiefly a protein mixture, with melittin at about 52 per cent of its peptides (Wikipedia, Apitoxin).

• Choosing ethanoic acid because acetic acid is the more familiar name.
• Not knowing that formic acid and methanoic acid are two names for the same compound.
• Assuming a fruit acid could also serve as an insect irritant.

As this source-of-acid recall, or reversed — naming the acid found in a given fruit, plant or insect.

• practice — not a real PYQ

  The acid present in the sting of an ant is

  • (a)citric acid
  • (b)methanoic acid
  • (c)oxalic acid
  • (d)lactic acid

  Answer(b) methanoic acid — also called formic acid, from formica, the Latin for ant.

• practice — not a real PYQ

  The acid present in vinegar is

  • (a)methanoic acid
  • (b)ethanoic acid
  • (c)tartaric acid
  • (d)citric acid

  Answer(b) ethanoic acid — vinegar is a dilute aqueous solution of ethanoic (acetic) acid.