Unit 3 Questions MEGATHREAD :)

[taqi]

How does decreasing the particle size of the stationary phase of a HPLC column SLOW all the component? from neap2010. i thought it would make them faster...less resistance and dispersion forces

[Water]

decreasing the particle size of the stationary phase, will increase the surface area for the interaction between the sample to the station phase. Greater interaction for dispersion force/whatever intermolecular bonding to occur.

[dmanz]

what is the iupac naming system? do we need to know it?

[tony3272]

You technically need to know it, but they say as long as there is only one structure which can be drawn from the systematic name you provide, then it is correct.

[dmanz]

You technically need to know it, but they say as long as there is only one structure which can be drawn from the systematic name you provide, then it is correct.

so what is it then? just another way of naming something?
what do you mean when you say only one structure can be drawn? what about isomers?

[tony3272]

You technically need to know it, but they say as long as there is only one structure which can be drawn from the systematic name you provide, then it is correct.

so what is it then? just another way of naming something?
what do you mean when you say only one structure can be drawn? what about isomers?

It's basically the recognized system for naming organic compounds. What i meant by only one structure, is that if you have something such as C4H8Cl2 and you are shown the structure, you must name it so that only the given structure can be drawn, not any isomers.

[Dr.Lecter]

do examiners care if you don't do 3D representations of structural formulae? are you in contravention of losing marks if you don't? (I'm clueless with 3D representations - I just make patterns because they are cool)

[thatricksta]

do examiners care if you don't do 3D representations of structural formulae? are you in contravention of losing marks if you don't? (I'm clueless with 3D representations - I just make patterns because they are cool)

You will get full marks if you draw your molecules at right angles and the bonds are to the right atoms.

[mickeymouse]

1) do alkanes have a higher boiling temperature than chloroalkanes? would increased branching result in a higher boiling temperature?

2) reacting a diprotic acid with a base would the ratio be 1 acid: 3 base?

[vea]

1) do alkanes have a higher boiling temperature than chloroalkanes? would increased branching result in a higher boiling temperature?

2) reacting a diprotic acid with a base would the ratio be 1 acid: 3 base?

1. Chloroalkanes have a higher boiling temperature than their respective alkane because the chlorine makes the molecule polar and so requires higher temperature to break the dipole-dipoles that may form. Increased branching results in a higher boiling point. I think this is because the branches start make dispersion forces with each other? Someone correct me if I'm wrong.

2. A diprotic acid has 2 protons to donate so you would need two bases (assuming it is a monoprotic base) to make up for it. The ratio is 1 acid: 2 base.


Question: A titration is performed to determine the concentration of a methanoic acid solution. Sodium hydroxide is used as the base. A suitable indicator to use for this titration would be?

Where do we have to assume the acid and the base are? Which is in the burette and which is in the conical flask and why? :S

[mickeymouse]

methanoic acid is a weak acid and sodium hydroxide is a strong base so the equivalence point would be a bit over pH7 from there I think you can determine a suitable indicator

hope that helps...

[DisaFear]

Friend asked me this, had no clue:

0.308g of an ester is reacted under reflux with 20ml of 1M of NaOH solution

What is a reflux?

[thushan]

@vea - in that kind of question it doesn't matter which reagent is in the burette or pipette as either way we would produce a colour change at endpoint, given we used a suitable indicator.

ALSO: This is an important point, but for organic chem where they ask you to draw structural formulas, NEVER use line drawings, even if they don't ask you to show all bonds, because there is a VERY HIGH chance you will be penalised. VCAA deems it too inaccurate (as line drawings don't show that you know that each carbon is bonded to 4 things).

[thushan]

@disafear -

Reflux is where you need to heat a liquid to boiling point but you don't want it to evaporate, so we stick in a condenser which essentially prevents any reagent being lost as vapour.

It doesn't change the nature of the question though, so don't worry about it

[nacho]

has anyone done the lisachem 08 chemical analysis test?
I've just lost a heap of confidence..

@vea - in that kind of question it doesn't matter which reagent is in the burette or pipette as either way we would produce a colour change at endpoint, given we used a suitable indicator.

ALSO: This is an important point, but for organic chem where they ask you to draw structural formulas, NEVER use line drawings, even if they don't ask you to show all bonds, because there is a VERY HIGH chance you will be penalised. VCAA deems it too inaccurate (as line drawings don't show that you know that each carbon is bonded to 4 things).

do you mean not to draw at 90 degree angles?
eg.      H     H
          |     |
      H - C - C - H
           |    |
           H    H
Oh wait i think i know what you mean
you mean where you dont show the carbons/other atoms involved