Chemistry 3/4 2013 Thread

[Edward21]

Well, I think you should know you can separate chemicals based on boiling points. That's really all there is to the 'principles of fractional distillation', and it's a pretty straightforward concept. It may not be mentioned explicitly, but I've come across a few worded questions asking how to obtain pure solutions of a substance, or separate a mixture of chemicals, and based on their boiling points is a pretty easy way to answer it.

The actual process of fractional distillation is not on the course though.

Like the 2011 U3 that asked about a pure product (ester) from distillation, but referred to IR data to confirm this. 

[lolipopper]

I Adding a catalyst
II Increasing temperature
III Increasing concentration
IV Increasing the surface area of the reactant

out of the following which ones always ensure an increase in reaction rate?

Answer : I, II, III

why is it not the case with surface area? and if surface area doesn't affect the rate, then why does increasing the concentration, because aren't both of them essentially doing the same thing [exposing more reactant particles to each other?]

[SocialRhubarb]

What if the reactant is gaseous?

[lolipopper]

What if the reactant is gaseous?

true. any other reasons?

[lzxnl]

How DO you define the surface area of a gas?

[SocialRhubarb]

How DO you define the surface area of a gas?

Arbitrarily.

[lzxnl]

Isn't that a contradiction? To define something arbitrarily?

[Aurelian]

Isn't that a contradiction? To define something arbitrarily?

I would've actually thought it was a tautology All definitions are "arbitrary" (at least in a logical sense)...

[lolipopper]

How DO you define the surface area of a gas?

doesn't a gaseous reactant have maximum surface area anyway?

[lzxnl]

You can't define the surface area of a gas I think

[Dismounted]

doesn't a gaseous reactant have maximum surface area anyway?

Yeah, you can't really increase the "surface area" of a gas since each molecule is already individually separated from one another.

[neonperson]

For VCAA 2012 U3 Short answer question 7) ai.

Why is the equation for the precipitate with the equilibirum arrows?
Here is link to assessor's report
http://www.vcaa.vic.edu.au/Documents/exams/chemistry/Chem1_assessrep_12.pdf

[lzxnl]

Precipitation is an equilibrium reaction too.

[neonperson]

Precipitation is an equilibrium reaction too.

Always?

[lzxnl]

ALWAYS.

It's just that sometimes, like the precipitation of iron hydroxide, you can't detect an equilibrium.