Question

1. Why is it important to chill the water that will be used for rinsing/washing the precipitate

2. In the synthesis of salicylic acid reaction, percent yield 75% - 85% are not uncommon. ( if the percent yiels are much higher it is likely that your product was still wet when you weighed it.) Explain why very high percent yiled (>95%) are not expected in this lab.

3.Compare the melting point ranges of the pure salicylic acid sample and your recrystallized product. How much do they differ (%). Explain this % error ( of the lower and upper temperatures of the range) in terms of the purity of your recrystallized product.

Melting range

pure salicylic acid= 157.4C- 160C

recrystallized product= 158.3C- 159C

Answer 1

1. The water must be chilled before using it to wash the precipitate or else, the precipitate which has greater solubility in warm water would dissolve and we would product loss and get lower yields.

2. some amount of salicylic acid is alaways lost during workup and acidification from aqueous solution. Therefore the yields are always in this range.

3. % error in melting point

= (158.7 - 158.65) x 100/158.7

= 0.03%

So the compound formed after recrystallization is sufficiently pure when compared to pure sample.