A. During a recrystallization and after a considerable amount of time cooling on

Question

A. During a recrystallization and after a considerable amount of time cooling on ice, no crystals have developed. Suggest two methods to induce crystallization.

B. An unknown compound Z is one of the four compounds listed in the table below. The unknown is purified by dissolving it in dichloromethane and washing it with aqueous sodium carbonate. Drying and evaporation of the dichloromethane yields a solid with a melting point of 102-114 oC.   After recrystallization from ethanol, the melting point is 120-122 oC. What is the identity of Z? Explain your reasoning.

Possible Compounds:

o-toluic acid mp=102

1,2-diaminobenzene mp=102

benzoic acid mp=122

ethyl butanoate mp=122

Explanation / Answer

A.

Consider decreasing amount of solvent, therefore, more solids will form.

Also , consider increasing temperature, i.e. if ice is at -5°C then try -10°C if possible, to decrease Temperature and decrease solubility, ie. incrase crystallisation

B.

If final melting point is 120-122 then ignore toluic acid an diaminobenzene

then

only bezoic acid and ethyl butanoate are possible

For the dchlorometane, try benzoic acid , since it is much more soluble than bezoic acid, so expect benzoic acid to form the solid

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

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