Chemistry Exam Revision Questions

[kenhung123]

Ok. As suggested by vexx, since I ask too many questions it is a good idea to start a thread.
Feel free to ask your questions here too..
Umm I'm wondering what does it mean when asked to discuss the physical and chemical properties of a molecule? What should I be thinking when asked that?

[kenhung123]

Is there any 'easy' way to determine whether a reaction is acid base? (Or do you just need to know your acids and bases and identify acid and base reactants)

[superflya]

when a salt + water form.

[Martoman]

If one H proton is obviously driven away and mopped up by the other reactant.

[kenhung123]

Thanks guys

Problem: Why is it a problem to directly titrate weak acid with weak base when you can simply use a strong acid or strong base to titrate? I mean why do we need to use back titration in that case? I know it doesn't produce sharp end pt but just use a strong acid/base and problem solved?

[Martoman]

This isn't a problem because you can use just that. This is just in the textbook to warn us of the folly of doing so and give us some intuition on the equivalence point...... i think. :laugh:

[kenhung123]

Hmm, I think there may be a reason otherwise back titration is almost useless

[Martoman]

Oh right, in that case its because of its low concentration that its more accurate to do so via back titration. There is also volatility to consider (although, this isn't really related to the question).

[Potter]

http://yfrog.com/16image0043kj

As requested.. I don't know if that's helpful or not.

Btw, N(alpha) = adjacent environment 1. N(beta) = adjacent environment 2.

Disclaimer - I'm not 100% sure on what I've written.. I just kinda put two and two together, so don't take this religiously. It was taken with a crappy phone camera, forgive me. Cbf to bring out the scanner.

[darkphoenix]

Is there meant to be a specific way to determine the number of isomers of a molecule?

Or do we have to sketch out each structural formula?

[superflya]

Is there meant to be a specific way to determine the number of isomers of a molecule?

Or do we have to sketch out each structural formula?

just have to draw em out, theres no formula.

[Potter]

Is there meant to be a specific way to determine the number of isomers of a molecule?

Or do we have to sketch out each structural formula?

I would say you would just have to sketch out each one..

-Edit
Beaten

[stonecold]

Is there meant to be a specific way to determine the number of isomers of a molecule?

Or do we have to sketch out each structural formula?

There was a thread on this a few weeks back.  Apparently if you can devise a formula that will give you the number of isomers for a molecule, then you would win the Nobel prize or something.

That's what TT said...

[Martoman]

http://yfrog.com/16image0043kj

As requested.. I don't know if that's helpful or not.

Btw, N(alpha) = adjacent environment 1. N(beta) = adjacent environment 2.

Disclaimer - I'm not 100% sure on what I've written.. I just kinda put two and two together, so don't take this religiously. It was taken with a crappy phone camera, forgive me. Cbf to bring out the scanner.

If this is a general rule which works for spin spin shit, me loves you long time.

Is there meant to be a specific way to determine the number of isomers of a molecule?

Or do we have to sketch out each structural formula?

http://vcenotes.com/forum/index.php/topic,25608.0.html


Usually if its i know that there are no isomers except if functional groups are involved (except carboxyl as that can't be swapped around in the middle!). For greater than this, know the carbon backbone isomers and work your way up.

ie for butane you can wrench the carbon off the end to branch off the middle one. So if Cl is a functional group, then you write out the backbone and put a "dot" where the Cl should be.

it can be on the end, and on the next carbon for the straight chain.

Then for the branched it can be on the first carbon on the branched or the other carbon in the straight 3 chain giving a total of 4.

[darkphoenix]

Ah ok fair enough. Thanks