Chemistry 3/4 2013 Thread

[Dismounted]

Yeah, that fact is alluded to in the general "rule" which you see in textbooks, where we consider anything with an equilibrium constant of greater than as "going fully in one direction".

In that specific Q, from reading it, it doesn't seem like there's anything that would allude to us having to consider it an equilibrium (in fact, the experiment would be pretty crap if it was a measurable equilibrium...). So I wouldn't worry about the arrow in that specific situation.

[Edward21]

With the pH of sulfuric acid. Let's say 0.05M? I know that you multiple the conc. by 2 for the [H3O+] and then go on as per normal. But I've seen examples in practice exams where they work about 0.05M and 0.1M and say the pH lies inbetween 1.3 and 1.0. What should I do on the exam if this comes up???

[lzxnl]

With the pH of sulfuric acid. Let's say 0.05M? I know that you multiple the conc. by 2 for the [H3O+] and then go on as per normal. But I've seen examples in practice exams where they work about 0.05M and 0.1M and say the pH lies inbetween 1.3 and 1.0. What should I do on the exam if this comes up???

Hydrogen sulfate is a weirdo. Its acidity constant is about 0.01 which is still a weak acid but quite a strong one. Still, I've done calculations and the final pH is closer to as of sulfuric acid is monoprotic
They won't ask thay without asking you to make an assumption somewhere I think.

[neonperson]

For the equation:

2CH₃OH(g) <--->CH₃OCH₃(g) + H₂O(g)

For the Ka expression, why is water in the equation?

[massachusetts8]

For the equation:

2CH₃OH(g) <--->CH₃OCH₃(g) + H₂O(g)

For the Ka expression, why is water in the equation?

Water is in gaseous state so you include it in the expression. When water is in (l) form you do not include it.

[Charvie]

Can someone please explain to me why this would be 4-methyl hexanoic acid and not 3-methyl hexanoic acid?
http://imgur.com/p1ktpYX

[Edward21]

Can someone please explain to me why this would be 4-methyl hexanoic acid and not 3-methyl hexanoic acid?
http://imgur.com/p1ktpYX

You have to number off your carbons from the most prominent functional group, the carboxyl one wins haha. If you work from right to left from the group you'll find it's 4. Btw, I'm pretty sure that looks like a NEAP exam if I'm correct? 

[Charvie]

You have to number off your carbons from the most prominent functional group, the carboxyl one wins haha. If you work from right to left from the group you'll find it's 4. Btw, I'm pretty sure that looks like a NEAP exam if I'm correct? 

Ah thats right, thanks for that

Sure is! 87% on that one. How do you think it'd translate to VCAA?

[Edward21]

Ah thats right, thanks for that

Sure is! 87% on that one. How do you think it'd translate to VCAA?

Well the best way is to do the VCAAs haha but NEAPs are quite reflective of VCAAs you could expect a similar score. Hopefully you can reach the A+ cutoff, you're sort of sitting on a very high A to low A+ with a percentage like that.

[Charvie]

Well the best way is to do the VCAAs haha but NEAPs are quite reflective of VCAAs you could expect a similar score. Hopefully you can reach the A+ cutoff, you're sort of sitting on a very high A to low A+ with a percentage like that.

I'd better tighten up on those errors then :S
thanks

I'd always thought that NEAP was much harder than VCAA typically though.

[Edward21]

I'd better tighten up on those errors then :S
thanks

I'd always thought that NEAP was much harder than VCAA typically though.

The problem with VCAAs lately is they've been really picky on certain areas in strange ways; NEAPs are generally harder but that doesn't stop VCAA from asking strange questions. 

[rabdog]

OMG I can't find my chemistry textbook!!!!! I so screwed 

[Dismounted]

The problem with VCAAs lately is they've been really picky on certain areas in strange ways; NEAPs are generally harder but that doesn't stop VCAA from asking strange questions. 

I found Neap exams to be a bit more mathematically-based than others (and the VCAA). That might suit some and not others.

The VCAA seems to be moving to more and more worded/explain type questions, rather than slogging out the maths.

[Edward21]

I found Neap exams to be a bit more mathematically-based than others (and the VCAA). That might suit some and not others.

The VCAA seems to be moving to more and more worded/explain type questions, rather than slogging out the maths.

Mmm I love my stoichiometry though  But yes I'm seeing the gravitation towards these explain intermolecular forces concepts and rate of reaction explanations; even more exotic are the critique the experiment ones that could come up on this year's paper! 

[massachusetts8]

Could someone please explain to me VCAA 2007 EXAM 1 MULTIPLE CHOICE Q16?
Thanks in advance