Astudent purified a 500-mg sample of phthalic acid by recrystallization from wat
ID: 1080238 • Letter: A
Question
Astudent purified a 500-mg sample of phthalic acid by recrystallization from water. The published solubility of phthalic acid in 100 mL of water is 0.54 at 14 "C and 18 g at 99 C (a) What is the smallest volume of boiling water the student could use to dissolve 500 mg of phthalic acid? Dissolution of phthalic acid in boiling water produced a dark-colored solution. The student allowed the solution to cool, added several spatulas full of activated carbon, and heated the mixture to boiling. After gravity filtration, the clear and colorless solution was alowed to cool to room temperature. Crystals formed, and the student isolated 380 mg of phthalic acid b) Calculate the percent recovery of phthalic acid in this experiment (c) Suggest one or more procedural errors the student made that couild be responsible for some loss of phthalic acidExplanation / Answer
a) At 99oC , i.e. , boiling water
18 g = 18000 mg phthalic acid dissoves in : 100 ml of water
1 mg phthalic acid dissolves in : 100/18000 ml of water
500 mg dissolves in : 500 * (100/18000) ml of water = 2.778 ml of water
b ) % recovery = (actual recovery/theoretical recovery) * 100
= (380/500) * 100 = 76 %
c) Possible procedural errors might have been :
i ) Activated Carbon adsorbs the impurity , i.e., molecules that causes colour. But using it more than the required amount may lead to adsorption of Phthalic acid to it. So excess of activated carbon used can be one souce of error
ii ) Other source of error can be the solution was not hot enough during gravity filtration leading to some of the Phthalic acid not soluble in the solution and getting filtrated out.
iii ) This might not seem very important but is a very relevant error that apparatuses used during this experiment wasn't clean enough.
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