Substance                                                            Melting Points in ℃ Benzoic acid                                                           122.3 ℃                          Succinimide                                                             125-127  Urea                                                                         133 ℃ Cinnamic acid (trans).                                          133 ℃ Thiourea                                                                 182 ℃ Hippuric acid.                                                        187 ℃   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.

Fundamentals Of Analytical Chemistry
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Chapter8: Sampling, Standardization, And Calibration
Section: Chapter Questions
Problem 8.16QAP
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Substance                                                            Melting Points in ℃

Benzoic acid                                                           122.3 ℃                         

Succinimide                                                             125-127 

Urea                                                                         133 ℃

Cinnamic acid (trans).                                          133 ℃

Thiourea                                                                 182 ℃

Hippuric acid.                                                        187 ℃

 

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.

 

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