INTEC Chemistry Blog

Archive for March 2013

Remember, your reports/essays/assignments etc, submitted for grading, must be your own work !!!.

Do not just copy your fellow students work and try to reword it. If you discussed something other your peers regarding some assignment etc, then you must go and write what you UNDERSTOOD from the conversations with your peers (and not a verbatim copy of your discussions). You must ‘process’ any information you get, either by reading a book, discussing it with your peers, from a video etc.

I have a low tolerance of people just copying.

CHM555 labs. Questions. Give brief but meaningful answer the questions.

Week 1. Experiment 1: Extraction of caffeine from a tea bag.

a) Caffieine acts as a base. What problem might occur if we did NOT add Na2CO3 to the boiled tea solution.
b) What part of the molecule is responsible for its basic behaviour
c) The % yield can vary. Give reasons why this may be.
d) Is DCM polar?
e) Propose an alternative solvent to DCM
f) What % of the tea bag was caffeine.
g) What errors/procedural steps may have decreased the yield of caffeine?
h) What may have caused an apparent increased the yield?
NEW:
Q1) What was the purpose of boiling the tea bag in water ?
Q2) Why not extract with just one large portion/volume of DCM instead of multiple small volumes of DCM>
Q3) Why use DCM instead of a different solvent like acetone?

Week 2. Experiment 2: Sodium Borohydride reduction of cyclohexanone.
Q1) What is the purpose of adding methanol to cyclohexanone?
Q2) Why was the mixture cooled after NaBH4 was added?
Q3) What was the gas observable as small bubbles after NaBH4 was added? and why was it produced?
Q4) Why was a test tube used instead of a separating funnel?
Q5) Comment on the yield of alcohol produced.

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.

Salam/Peace

Here’s the slides that I’ve used in class. Please visit the sites I mention. Some of the links/videos are local links so unless you have the actual video and in the same place as the powerpoint file, you wont be able to watch the video. You can get those particular video’s  from me in the class.

Presentation1 11-3-2013

Hello CHM456 students. You can get to the CHM456 ‘homepage’ by clicking the link on the right or by using this link: https://intechemistry.wordpress.com/2012/09/10/chm456-organic-page/

On that homepage, you will find links to individual topics that we will study in this course. Some of the links have no content yet, but please feel free to leave comments regarding anything we have done in the class (or what you have read from your a books/course materials).

I can give give you the password for the file vault in class. Please do not put the password on the internet. Thank you.

I will update the assignment later. Last sem students had to produce a ‘video’ on one of the topics. I’m thinking of changing that now to having to review three to five websites on a particular topic. If I do this, you will be working in groups (as was the case for the video assignment). There will be guidelines and a set of questions issued.


March 2013
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