7. You Want to purify 10 grams of benzoic acid that has been contaminated with 0
ID: 873725 • Letter: 7
Question
7. You Want to purify 10 grams of benzoic acid that has been contaminated with 0.2 g of salicylic acid. You have found the following data by looking the Merck Index: a) What volume of Boiling water is needed to dissolve the 10 g of benzoic acid? (show calculations) b) How much benzoic acid will crystallize after cooling to 20 degree C (show calculations) c) Will any salicylic acid crystals form? Why or why not? (show calculations/ reason for answer) d) What is the maximum amount of benzoic acid that could be recovered in the first crop of this recrystallization? (Show calculations) e) Will the benzoic acid be pure? Why or why not?Explanation / Answer
a) See it is given in the table
0.68 g of benzoic acid is dissolved by 10 mL of boiling water
So 1 g of benzoic acid is dissolved by 10/0.68 mL of boiling water
Hence 10g of benzoic acid is dissolved by (10/0.68) x 10 mL of boiling water = 147.05 mL of boiling water
b) Here we will find that how much benzoic acid will be soluble at 20C in 147 mL of water. Using above table
0.029 g/10 mL = x g/ 147mL
solve, and x = 0.43 g is soluble at 20C, Now as we started with 10.0 g, 9.6 g of benzoic acid will crystallize.
c) Here we will find that how much salicylic acid will be soluble at 20C in 147 mL of water. Using above table
0.22 g/10mL = x g/147 mL
solve, and x = 3.2 g. Since you only had 0.2 g salicylic acid, therefore all of it will be soluble when the solution is chilled.
d) 9.6 g From (b),
e) Yes, We can see from (c) since all of the salicylic acid will be soluble at 20C in 147 mL of water.
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