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quarkboy
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Recrystallization Questions - help needed urgent!
I can't figure this out, please help... I will update with answers as I get them.
1. Compound A has a solubility in ethyl acetate of 18 mg per 50 mL at 20 Celsius, and a solubility of 0.28g per 50 mL at 75 Celsius.
You are given a sample of 0.800g compound A which is contaminated with 2 mg of compound B.
(a). If compound B is always completely soluble in ethanol, how could you purify compound A? Would the result of this purification be 100% pure A? Explain.
Ans: Recrystallization method must be followed as per lab practice. However, since compound B dissolves completely in the solvent we are able to obtain a pure end product.
(b). If compound B has approx. the same values of solubility in ethyl acetate as compound A, how could you purify compound A? Would the result of this purification be 100% pure A? Explain.
Ans: As above, however mixed melting points must be used to identify the compound A. It will not be completely pure as an end-product.
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3. The solubility of an unknown compound, C, in ethanol is 24mg per 100 ml at 20 Celsius and 0.78g per 50ml at 90 Celsius.
(a). Calculate the min. amount of ethanol needed to recrystallize 2.4g of compound C.
Ans: 0.78g/50ml * 0.024g/x ; x = 158.3ml of ethanol required [90 Celsius]
(b). Calculate the amount of compount C recovered by filtration at 20 Celsius from this min. amount of ethanol.
Ans: 158.3ml (as above) * 24mg/100ml = y
Therefore, 2.4g - y = amount of ethanol [20 Celsius]
I can't figure this out, please help... I will update with answers as I get them.
1. Compound A has a solubility in ethyl acetate of 18 mg per 50 mL at 20 Celsius, and a solubility of 0.28g per 50 mL at 75 Celsius.
You are given a sample of 0.800g compound A which is contaminated with 2 mg of compound B.
(a). If compound B is always completely soluble in ethanol, how could you purify compound A? Would the result of this purification be 100% pure A? Explain.
Ans: Recrystallization method must be followed as per lab practice. However, since compound B dissolves completely in the solvent we are able to obtain a pure end product.
(b). If compound B has approx. the same values of solubility in ethyl acetate as compound A, how could you purify compound A? Would the result of this purification be 100% pure A? Explain.
Ans: As above, however mixed melting points must be used to identify the compound A. It will not be completely pure as an end-product.
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3. The solubility of an unknown compound, C, in ethanol is 24mg per 100 ml at 20 Celsius and 0.78g per 50ml at 90 Celsius.
(a). Calculate the min. amount of ethanol needed to recrystallize 2.4g of compound C.
Ans: 0.78g/50ml * 0.024g/x ; x = 158.3ml of ethanol required [90 Celsius]
(b). Calculate the amount of compount C recovered by filtration at 20 Celsius from this min. amount of ethanol.
Ans: 158.3ml (as above) * 24mg/100ml = y
Therefore, 2.4g - y = amount of ethanol [20 Celsius]
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