Question

In regards to this question about Digestion which statement would be true?

Which of the following statements is true regarding the digestion of a precipitate in its mother liquor?

1. A lengthy digestion is inadvisable because more impurities can become entrapped in the growing crystals.

2. An elevated temperature, during digestion, is used to impede the coagulation of a colloidal precipitate through increased kinetic energy of the solution.

3. Digestion promotes recrystallization of a precipitate, thereby increasing particle size and redissolving adsorbed impurities.

4. The purity of the precipitate improves during digestion because smaller particles are produced thus reducing the amount of absorbed impurities.

Answer 1

The filterability of precipitates is improved by promoting the growth of large particles. This process is known as digestion.

When a precipitation reaction leads to the formation of very small particles, the solution is said be a colloidal suspension These colloidal particles can be converted into large particles by precipitating from a hot solution (mother liquor) and allowing the precipitate to stand for an hour or so before filtration. The process of convert small colloidal particles to large filterable particles is called coagulation. Hence, the second statement is wrong; digestion actually promotes coagulation.

The fourth statement is incorrect because digestion converts small particles into large particles.

The first statement is incorrect because during digestion, the precipitate is allowed to stand for atleast one hour or more to remove trapped impurities.

The correct statement is actually the third statement; digestion improves particle size and re-dissolves impurities in the mother liquor (ans).