For Questions 1-3 assume that you were given 5.00 g of an unknown A for this lab, one of the six compounds whose melting points you looked up for prelab.  1.  You recrystallized A and obtained 2.23 g pure product.  What was your percent recovery?  That is, what percent of the original mass did you get back?  Show your work.   2.  Assume you took the melting point of the pure product and it was 123oC.  Considering the melting points you looked up for prelab, which compounds could you narrow down the identity of A to?  Explain.   3.  Assuming there are pure samples of all six possible unknowns available, how could you determine exactly which unknown you have?  Explain what you would do, and what the results would show.

Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
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For Questions 1-3 assume that you were given 5.00 g of an unknown A for this lab, one of the six compounds whose melting points you looked up for prelab. 

1.  You recrystallized A and obtained 2.23 g pure product.  What was your percent recovery?  That is, what percent of the original mass did you get back?  Show your work.

 

2.  Assume you took the melting point of the pure product and it was 123oC.  Considering the melting points you looked up for prelab, which compounds could you narrow down the identity of A to?  Explain.

 

3.  Assuming there are pure samples of all six possible unknowns available, how could you determine exactly which unknown you have?  Explain what you would do, and what the results would show.

 

Substance                                                            Melting Points in ℃

                                 

Benzoic acid                                                           122.3 ℃                         

Succinimide                                                             125-127 ℃

Urea                                                                         133 ℃

Cinnamic acid (trans).                                               133 ℃

 Thiourea                                                                    182 ℃

Hippuric acid.                                                             187 ℃

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