INTEC Chemistry Blog

CHM 412 lab questions for Exp 1 and 2.

Posted on: March 30, 2013

Salam. Be brief and to the point when answering these questions.

I advise copy and pasting them into a document and either typing the answers out in a few lines below the question followed by printing, or, printing out the questions and then writing the answers by hand in a few sentences. Don’t waste time handwriting out the Q’s

The questions are asked to try to ensure you understand why certain steps were done. If you worked/discussed as a group to try and get the right answer, you MUST then go away and write YOUR own understanding of the answer. If you don’t know the answer, have a guess – an intelligent guess..

Week 1. Experiment 2: recrystallization of acetanilide.
1) Soluble and insoluble impurities were removed in this process.
a) What steps of the procedure were used to remove
i) the soluble impurities
ii) the insoluble impurities.

2) What main property/properties should the solvent have to make it a suitable choice for use in a recrystallization?>

3) After hot filtration the solution is allowed to cool to room temperature. What is the purpose of cooling the solution in ice after the hot filtration is allowed to reach room temperature.

4) The crystals must be dry for the melting point. Why is this?

5) The melting point should be done at least twice.
a) Why is it common for two melting points to be done?
b) Why does the melting point equipment have to cool before the second melting point is done?

6) Why is sometimes the observed melting point lower than the literature value.

7) What information can you get from a melting point?

CHM412 labs. Questions.
Week 2. Experiment 1: Extraction of toluene.

1) Three colourless liquids were used in this extraction. water, toluene and ether.
a) Categorise the following as polar or non-polar.
Water, Toluene.
b) Ether is weakly polar and so generally classified as non-polar. Which substance
will best dissolve in it? Water or toluene?
c) Why was a solvent like ethanol not used instead of ether

2) How can you tell which solvent forms which layer In the separating funnel?

3) Many students only recover a few cm3 of ether after distillation.
Give some reasons why (apart from human error, like spilling it).

4) Why was the (previously) anhydrous MgSO4 (or CaCl2 or Na2SO4) filtered off before final distillation.

5) Explain how one can know when a particular compound of a mixture is distilling off.

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