Chapter 15, Problem 6Q

Interpretation Introduction

Interpretation:

The change in the recrystallization procedure to ensure good crystals should be determined.

Concept introduction:

Recrystallization is a process in which an impure crystalline solid dissolved in hot solvent precipitates back when the solvent is cooled and that leads to formation of pure solid crystals. For successful recrystallization, maximum solubility of solute in hot solvent is essential and in cold solvent the solubility should be minimum for the maximum yield of crystals.

If solute will have good solubility in cold solvent, there will be loss of compound on recrystallization. To minimize this loss, the choice of the solvent for recrystallization is important.

When a solute is dissolved in an appropriate solvent at an appropriate rate, temperature and concentration then it results in the formation of perfect crystal.

A perfect crystal is obtained when an impure solute is dissolved in an appropriate recrystallization solvent at an appropriate concentration. The impure solid when dissolved in an appropriate hot solvent, its impure crystal lattice gets destroyed. On recrystallization from the cool solvent, a new and pure and perfect crystal is obtained.

The rate of crystal growth has a huge impact on the purity of the recrystallized compound. Slow cooling or crystal formation from a saturated solution provides more time to the impurities and therefore they do not fit into the crystal lattice and settle down at the bottom of the solution. A large and pure crystal is obtained from slow cooling.

Rapid crystal formation leads to entrapment of the impurities in the crystalline solute when the crystal formation occurs.