Why does adding a dilute weak acid, such as ethanoic acid (), to fresh liquid latex cause it to coagulate rapidly into a solid mass?

Answer and explanation

Correct answer: C. Hydrogen ions neutralize the negative charges on protein membranes of rubber particles

  1. Step 1: Analyze latex colloidal stability: natural rubber particles are suspended in serum, enveloped by an outer protective membrane of proteins carrying net negative charges that repel one another.
  2. Step 2: Adding acid supplies positive hydrogen ions () that neutralize these negative surface charges. The uncharged rubber particles collide, rupture, and entangle into an irreversible coagulated coagulum.
Answer
Hydrogen ions neutralize the negative charges on protein membranes of rubber particles.
Why not the others: 'Acid molecules dissolve the polyisoprene chains, converting rubber into a gas' is false as rubber does not vaporize; 'Acid reduces the temperature of the latex below the freezing point of water' is physically false; 'Acid catalyzes rapid dehydration synthesis of sulfur cross-links in the latex' describes vulcanization, not acid coagulation.

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