Hi this organic chemistry questions is for the synthesis of benzoin lab. The fol

Question

Hi this organic chemistry questions is for the synthesis of benzoin lab. The following are its procedures that lead up to the question.

1. Place 0.7g of thiamine hydroclhloride and 2 mL of water in a 50 mL erlenmeyer flask.

2. After all the thiamine has dissolved, add 7 mL of ethyl alcohol and 2.5 mL of 3 M sodium hydroxide.

3. To the yellow solution, add 4 mL of benzadlehyde.

4. Vaccum filter the crystals, and wash them with 10 mL of cold 50% aqueous ethanol.

My question is Why is a mixture of water and ethanol used to wash the crystals?

Explanation / Answer

Ans. There are two types of contaminating traces in the crystals-

            Organic (benzaldehyde- insoluble in water but soluble in ethanol), and

            Inorganic (NaOH- lower in ethanol but highly soluble in water)

The water- ethanol mixture acts as a good solvent that removes the traces of both organic and inorganic impurities simultaneously leaving behind pure crystals.

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.