INTEC Chemistry Blog

Answers to polar molecules exercises Here you are, the answers to these questions (in microsoft word “.doc” format)

 

 

Test is NOW scheduled to take place during your theory time.

The topics will be the same.

See you there.

Will be held on Monday night, 7th April 2014. About 8:00pm.
Venue = Somewhere…
I’ll update this page when I’ve got a suitable place.

Test will cover anything from the following…

 

Structure of carbon compounds
The nature of chemical bonding: Covalent bonding
Polar and nonpolar molecules
Intermolecular forces
Hybridization: sp3, sp2, sp 
Functional groups
Empirical, molecular and structural formula
Structural isomerism: chain, position & functional group
Cis-trans isomerism
Homolytic and heterogenic breaking of covalent bond
Homogenic and heterogenic formation of covalent bond

In the lab this week, CHM456 (AS202) students were reporting “strange” ranges for their melting point determinations. e.g. 60-150oC.

Most of the pure compounds we use should have melting point ranges within one, two or three degrees only. Hence I think it’s fair to say students don’t really understand what it is they need to see in order to get the melting point range.

I must say, that I’m struggling to understand how this could be. I’d would have thought it quite easy to understand what the process of melting looks like.

Nevertheless, I do understand that what is obvious to an experienced person can be very non-obvious to someone with no experience.

Unfortunately, it’s not feasible or possible to show 20+ students what it looks like during a lab session.

But this site does a good job. It shows a sequence of frames (animated gif) showing what you should see in the melting process.

http://www.csi.edu/ip/physci/faculty/rex/MPMain.htm

Another source showing it is here: https://www.youtube.com/watch?v=9aQio1KQKrs (1min 37seconds in)

Yet another one here:

(melting begins about 3mins 18 seconds in)

And here too:

(about 6min 40s into the video)

Please do watch ALL of the videos. They are short.

This one is longer, but still worth watching I feel.
https://www.youtube.com/watch?v=zMjl9MzpySU (starts about 20min 20s in)

Actually this highlights an important point. Studying has NEVER EVER been EASIER. The amount of resources and information available is simply stunning. You just have to put the time in and do the reading or even easier, watch the videos.

Sketch the following molecules and deduce whether the following molecules are polar or non-polar.

1) chloromethane, CH3Cl

2) Propanone, CH3COCH3

3) tetrachloromethane, CCl4

4) phosphine, PH3

5) Cyclohexane, (CH2)6

6) Ethylamine, CH3CH2NH2

7) Carbon monoxide, CO

8) Iodine, I2

9) propene, H2CCHCH3

10) phosphorous pentachloride, PCl5

11) Sulfur trioxide, SO3

12) Methane, CH4

- Answers will be posted later in the comments.

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