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Maximum Percent Recovery

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JameB
#1
Nov23-11, 06:11 PM
P: 25
1. The problem statement, all variables and given/known data

Solubility of acetanilide in water is
5.5g/100mL at 100C
0.53g/100mL at 0C

A 0.150g sample of acetanilide containing only traces of impurities was recrystalized using a total of 3mL of hot water.

a) What is the maximum possible percent recovery of pure acetanilide? Show all steps...

b) By how much would the % recovery be reduced if, during vacuum filtration, the crystals were washed with a total of 20mL of ice cold water?

2. Relevant equations

Percent recovery equation and basic mathematical operations...

3. The attempt at a solution

for a) :=
mass that was recrystallized is 0.150g (is this correct assumption?)
maximum acetanilide that could dissolve in water at 100C is 0.165g (100mL = 5.5g then how much is 3mL...)

which implies that max recovery is (0.15/0.165)*100% = 90.9%

Is this right??!

for b) :=
amount that could dissolve in 20mL cold water= 20*0.53/100 = 0.106g

which implies that amount recovered = 0.150-0.106g = 0.044g

which implies that percent recovery is 0.044/0.165*100 = 26.7%

which means that % recovery will be reduced by 64.2%

Am I correct? Thanks :)
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chemisttree
#2
Nov23-11, 07:46 PM
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Quote Quote by JameB View Post
1. The problem statement, all variables and given/known data

Solubility of acetanilide in water is
5.5g/100mL at 100C
0.53g/100mL at 0C

A 0.150g sample of acetanilide containing only traces of impurities was recrystalized using a total of 3mL of hot water.

a) What is the maximum possible percent recovery of pure acetanilide? Show all steps...

b) By how much would the % recovery be reduced if, during vacuum filtration, the crystals were washed with a total of 20mL of ice cold water?

2. Relevant equations

Percent recovery equation and basic mathematical operations...

3. The attempt at a solution

for a) :=
mass that was recrystallized is 0.150g (is this correct assumption?)
maximum acetanilide that could dissolve in water at 100C is 0.165g (100mL = 5.5g then how much is 3mL...)

which implies that max recovery is (0.15/0.165)*100% = 90.9%

Is this right??!
You are using the solubility of this material at 100C which is good to know but when you recrystallize it the temperature is lowered to near freezing (if you are doing it right). So how much would you lose in 3mL of water at 0C?
JameB
#3
Nov23-11, 08:36 PM
P: 25
Quote Quote by chemisttree View Post
You are using the solubility of this material at 100C which is good to know but when you recrystallize it the temperature is lowered to near freezing (if you are doing it right). So how much would you lose in 3mL of water at 0C?
I would lose 0.0159 at 0C from 0.150g right? (or from 0.165g?)

if I lose 0.0159 then my max percent recovery is [(0.150-0.0159)/0.150]*100=89.4%

Yes?

chemisttree
#4
Nov24-11, 09:03 AM
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Maximum Percent Recovery

I'm not going to check your math but using the cold water solubility is certainly the way to go.


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