Chemistry 2014 Predictions?

[speedy]

I know it's probably a little early, but any thoughts? Especially for the final/extended answer question

[Jcp34]

Not much on chromatography or spectroscopy on last year's exam, so that might be covered more heavily. Also, only a very simple acidity constant question on the SA last year, so maybe expect some more tricky questions regarding that topic. Electrolysis and Le Chatelier's principle were covered well last year, and I think people performed decent on these topics, so maybe not so much of these.

As for the last question, is it necessarily extended-response? 

[Reus]

Is there not always a pattern of an experiment done where we correct the mistakes or whatnot?

[Yacoubb]

I know it's probably a little early, but any thoughts? Especially for the final/extended answer question

*I think they'll have a back titration question. In my opinion it would be a good way to actually bring together a lot of different topics, and assess them in the realm of a back titration question.
*I think they'll definitely have us look at errors in experiments/effects these would have on the final results of our quantitative or qualitative analysis.
*I think they'll have a typical NMR/IR/Mass Spec question where we'll be required to discuss what compound we have under investigation, draw out the compound, etc.
* BIOFUELS - I think a lot of students don't really study these, and so I think if they wanted to be really sneaky, they could make a whole short answer question on biofuels, and ask the differenence between renewable/non-renewable, etc.
* They could delve into reaction rates. Have maybe a full question on reaction rates + perhaps the reaction being an equilibrium one.
* As someone mentioned, acid-base equilibria. Percentage dissociation, the self-ionisation of water, maybe calculations of pH, etc.

hopefully the exam is a step up in difficulty from the 2013 paper just to get those scores for A+ a little lower. I know that losing 10-12 marks last year netted you a 45. We'll see how it goes, I'm interested to see what others think.

P.S. Extended response question? I think this is from the VCAA sample paper? Yeah, that's just another example of a question where we'd be required to assess the experiment, possible limitations and modifications, etc to enhance the reliability of the results obtained.

[Reus]

hopefully the exam is a step up in difficulty from the 2013 paper just to get those scores for A+ a little lower. I know that losing 10-12 marks last year netted you a 45. We'll see how it goes, I'm interested to see what others think.

Do you know how many possible marks can be dropped for a 40?

[Yacoubb]

Do you know how many possible marks can be dropped for a 40?

I'm not too familiar with scores required for 40+ study scores in Chemistry. I only know that because I asked a friend about their score and their corresponding exam grades. But I'd imagine scoring an A+, given good ranking and all the other factors, would net you a 40+.

[momo123]

the fact that it's 13 pages longer than last year scares me. ant suggestions as to why? can't all be diagrams..

[Yacoubb]

the fact that it's 13 pages longer than last year scares me. ant suggestions as to why? can't all be diagrams..

Just remember that sometimes two MC questions can be placed onto one page. We may also be given space to draw things. Also, graphs to sketch? We may be required to construct a calibration curve. Don't be daunted VCAA wont set something that is impossible to finish (said no one ever LOL). But yeah in all seriousness, you'll be fine!

[Edward21]

Since titration curves is now a specific dotpoint in the study design, you may be asked to draw one, and explain why the equivalence point is where it is. Soooooo many students would say for NaOH and CH3COOH that the end point is above 7 because you're using the strong base, the answer is you're producing CH3COO- (ethanoate) conjugate BASE!! Always look at the salt produced at the equivalence point 

[All†Fiction]

Since titration curves is now a specific dotpoint in the study design, you may be asked to draw one, and explain why the equivalence point is where it is. Soooooo many students would say for NaOH and CH3COOH that the end point is above 7 because you're using the strong base, the answer is you're producing CH3COO- (ethanoate) conjugate BASE!! Always look at the salt produced at the equivalence point 

So does that mean Cl- is a weak base as well (conj base of HCl)? If so, why does the titration of HCl and NaOH still have an end point at 7, and not higher (Surely not because the Na+ ion is acidic or something)?

Thank you!

[thushan]

A strong acid has a conjugate base that is unbelievably weak, so weak that it barely even accepts protons (eg. HCl is a strong acid, but when was the last time you've heard of a solution of NaCl causing the pH of a solution to rise?)

A weak acid has a conjugate base that is weak - but not unbelievably weak. CH3COOH is a weak acid, and CH3COO- is a weak base.

Analogy:

HCl is a married couple with H+ and Cl-. H+ (the guy) and Cl- (the girl) have been married for 20 years. Married in name only. Cl- is not a particularly easy person to get along with, she's quite an unpleasant character. So when you dunk HCl in water, there's a lot of O(2-) ions (other girls) that makes H+'s eyes go O.O. On the down side, there are already two damned guys (H+'s) with each girl - hence why it's H2O. So, at the first opportunity, H+ divorces Cl- and has the time of his life with his...rendevous...with the O(2-)'s, joining the other two H+s to form H3O+

Meanwhile, Cl-, her husband having just left her, tries to find another man. But she finds that no man is interested in her because she's such an unpleasant character; the men would rather be with the O(2-)'s.

In contrast...

CH3COOH is a relatively ok married couple. They have their ups and downs. H+ likes CH3COO-, she's quite nice, but H+ wishes he can have a few on the side. So when CH3COOH enters water...some of the H+ goes "ah, there are some nice looking girls over there each with two men" and then they leave the CH3COO-.

The CH3COO-, being nice enough, manages to attract her ex-husband back, to form CH3COOH again. But the husband cheats on her again and leaves, and comes back again, and leaves...etc. There's a reversible reaction. CH3COOH is a weak acid and CH3COO- is a weak base, but a reasonable base.

Yet in contrast...

H2 is the happiest married couple with H+ adoring the lovely, amazing, beautiful H-. So when you dunk H2 in water...the H+ will see the O(2-) each with two men (to form H2O) and will be like "huh, why do I need those girls when I have my H- babe". So it's impossible to separate these two.

But suppose you dunk H- in water...

When she enters the water, all the H+ who are frolicking with the O(2-)s will turn their heads and stare at her longingly. Before long, they rush away from their O(2-)s and savagely compete for the H-. Eventually, you end up with happily married H2, and some of the O(2-)s only having one man (to form OH-). And that's why H- is a strong base.

A ridiculously unbelievably weak acid like H2 will have a strong conjugate base like H-.

Hope this makes sense...!

[Reus]

A strong acid has a conjugate base that is unbelievably weak, so weak that it barely even accepts protons (eg. HCl is a strong acid, but when was the last time you've heard of a solution of NaCl causing the pH of a solution to rise?)

A weak acid has a conjugate base that is weak - but not unbelievably weak. CH3COOH is a weak acid, and CH3COO- is a weak base.

Analogy:

HCl is a married couple with H+ and Cl-. H+ (the guy) and Cl- (the girl) have been married for 20 years. Married in name only. Cl- is not a particularly easy person to get along with, she's quite an unpleasant character. So when you dunk HCl in water, there's a lot of O(2-) ions (other girls) that makes H+'s eyes go O.O. On the down side, there are already two damned guys (H+'s) with each girl - hence why it's H2O. So, at the first opportunity, H+ divorces Cl- and has the time of his life with his...rendevous...with the O(2-)'s, joining the other two H+s to form H3O+

Meanwhile, Cl-, her husband having just left her, tries to find another man. But she finds that no man is interested in her because she's such an unpleasant character; the men would rather be with the O(2-)'s.

In contrast...

CH3COOH is a relatively ok married couple. They have their ups and downs. H+ likes CH3COO-, she's quite nice, but H+ wishes he can have a few on the side. So when CH3COOH enters water...some of the H+ goes "ah, there are some nice looking girls over there each with two men" and then they leave the CH3COO-.

The CH3COO-, being nice enough, manages to attract her ex-husband back, to form CH3COOH again. But the husband cheats on her again and leaves, and comes back again, and leaves...etc. There's a reversible reaction. CH3COOH is a weak acid and CH3COO- is a weak base, but a reasonable base.

Yet in contrast...

H2 is the happiest married couple with H+ adoring the lovely, amazing, beautiful H-. So when you dunk H2 in water...the H+ will see the O(2-) each with two men (to form H2O) and will be like "huh, why do I need those girls when I have my H- babe". So it's impossible to separate these two.

But suppose you dunk H- in water...

When she enters the water, all the H+ who are frolicking with the O(2-)s will turn their heads and stare at her longingly. Before long, they rush away from their O(2-)s and savagely compete for the H-. Eventually, you end up with happily married H2, and some of the O(2-)s only having one man (to form OH-). And that's why H- is a strong base.

A ridiculously unbelievably weak acid like H2 will have a strong conjugate base like H-.

Hope this makes sense...!

That is the best thing I've read in my life

[Edward21]

A strong acid has a conjugate base that is unbelievably weak, so weak that it barely even accepts protons (eg. HCl is a strong acid, but when was the last time you've heard of a solution of NaCl causing the pH of a solution to rise?)

A weak acid has a conjugate base that is weak - but not unbelievably weak. CH3COOH is a weak acid, and CH3COO- is a weak base.

Analogy:

HCl is a married couple with H+ and Cl-. H+ (the guy) and Cl- (the girl) have been married for 20 years. Married in name only. Cl- is not a particularly easy person to get along with, she's quite an unpleasant character. So when you dunk HCl in water, there's a lot of O(2-) ions (other girls) that makes H+'s eyes go O.O. On the down side, there are already two damned guys (H+'s) with each girl - hence why it's H2O. So, at the first opportunity, H+ divorces Cl- and has the time of his life with his...rendevous...with the O(2-)'s, joining the other two H+s to form H3O+

Meanwhile, Cl-, her husband having just left her, tries to find another man. But she finds that no man is interested in her because she's such an unpleasant character; the men would rather be with the O(2-)'s.

In contrast...

CH3COOH is a relatively ok married couple. They have their ups and downs. H+ likes CH3COO-, she's quite nice, but H+ wishes he can have a few on the side. So when CH3COOH enters water...some of the H+ goes "ah, there are some nice looking girls over there each with two men" and then they leave the CH3COO-.

The CH3COO-, being nice enough, manages to attract her ex-husband back, to form CH3COOH again. But the husband cheats on her again and leaves, and comes back again, and leaves...etc. There's a reversible reaction. CH3COOH is a weak acid and CH3COO- is a weak base, but a reasonable base.

Yet in contrast...

H2 is the happiest married couple with H+ adoring the lovely, amazing, beautiful H-. So when you dunk H2 in water...the H+ will see the O(2-) each with two men (to form H2O) and will be like "huh, why do I need those girls when I have my H- babe". So it's impossible to separate these two.

But suppose you dunk H- in water...

When she enters the water, all the H+ who are frolicking with the O(2-)s will turn their heads and stare at her longingly. Before long, they rush away from their O(2-)s and savagely compete for the H-. Eventually, you end up with happily married H2, and some of the O(2-)s only having one man (to form OH-). And that's why H- is a strong base.

A ridiculously unbelievably weak acid like H2 will have a strong conjugate base like H-.

Hope this makes sense...!

Oh wow, that is some legit chemistry prose.

[vcestudent123]

A definition question regrading something related to Chromatography and/or spectroscopy

[thushan]

That is the best thing I've read in my life

Heheh. I teach my students this analogy all the time.