Author Question: During a crystallization, while heating a solution of a compound to dissolve it in hot solvent, you ... (Read 74 times)

wenmo · **on:** Aug 23, 2018

During a crystallization, while heating a solution of a compound to dissolve it in hot solvent,
you boil it so long that a substantial amount of the solvent evaporates. What is likely to happen to some of the solute? What should you do if this occurs?

Question 2

Consider a sample of 1.0 g of benzoic acid contaminated with 1.0 g of salicylic acid.
(a) What volume of boiling water irs needed to dissolve the 1.0 g of benzoic acid?
(b) How much benzoic acid will crystallize after cooling to 20C?
(c) Will any salicylic acid crystals also form?
(d) Will the benzoic acid be pure?

onowka · **Reply #1 on:** Aug 23, 2018

Answer to Question 1

Some of the solute is likely to come out of solution because of the reduced amount of solvent
present. Add fresh solvent to the flask if you notice crystal formation in the hot solvent.

Answer to Question 2

(a) 0.68 g/10 mL = 1 g/X mL, X = 14.7 mL.
(b) In 14.7 mL at 20, 0.029 g/10 mL = X g/14.7 mL, X = 0.043 g benzoic acid would be in solution, thus 1.0 g 0.043 g = 0.96 g benzoic would crystallize.
(c) In 14.7 mL of solvent, the amount of salicylic acid in solution at 20 is X/14.7 mL = 0.22 g/
10 mL, and X = 0.32 g. Since there was 1.0 g of salicylic acid present, 1.0 g 0.32 g or 0.68 g
of salicylic acid crystals will form.
(d) No, it will be contaminated with 0.68 g of salicylic acid.