HSC 2012-2015 Chemistry Marathon (archive) (2 Viewers)

[Drsoccerball]

re: HSC Chemistry Marathon Archive

awk moment when they're basically the same

not really.. Its just teaching people to work with log..

 

[SuchSmallHands]

Chemistry marathon 2015

not really.. Its just teaching people to work with log..

Which isn't something you're required to do in this course. Your questions would probably be a lot more relevant if you took them from past papers until you're more familiar with how the HSC phrases its questions.

 

[InteGrand]

re: HSC Chemistry Marathon Archive

Find the pH of a 0.17 mol/L solution without using log.(Use Ln)

Let the concentration of hydrogen ions be (which is unknown, since we don't know anything about the acid or base in the solution).

Then by definition, using change of base formula and without using base 10 for the log, .

Not really sure what the point of this is though, since it's a less simplified form than leaving it in base 10.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Let the concentration of hydrogen ions be (which is unknown, since we don't know anything about the acid or base in the solution).

Then by definition, using change of base formula and without using base 10 for the log, .

Not really sure what the point of this is though, since it's a less simplified form than leaving it in base 10.

Its

Then type in calculator to find pH

 

[InteGrand]

re: HSC Chemistry Marathon Archive

Its

Then type in calculator to find pH

You've said the solution is 0.17 mol L^-1, but that's not necessarily the concentration of H⁺.

And you forgot a negative sign, since pH = -log₁₀[H⁺].

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Can you use Latex for these type of question.

Nope, this answer is incorrect (was on tapatalk earlier and couldn't see the response). Can any 15ers pick up on what's wrong with this?

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Find the pH of a 0.17 mol/L solution without using log.(Use Ln)

I don't think a question can get more pointless than this...

 

[Fizzy_Cyst]

re: HSC Chemistry Marathon Archive

A galvanic cell was set up using (amongst other things) copper electrode, magnesium electrode, 100mL 1M Copper Nitrate solution and 100mL 1M Magnesium Nitrate solution

After a few minutes, student takes apart the galvanic cell and notices that a solid deposit of 1.473g has occurred on one of the electrodes

(A) identify the solid deposit and on which electrode it occurred

(B) calculate the final concentration of nitrate ions in the magnesium nitrate solution

 

[Librah]

re: HSC Chemistry Marathon Archive

A galvanic cell was set up using (amongst other things) copper electrode, magnesium electrode, 100mL 1M Copper Nitrate solution and 100mL 1M Magnesium Nitrate solution

After a few minutes, student takes apart the galvanic cell and notices that a solid deposit of 1.473g has occurred on one of the electrodes

(A) identify the solid deposit and on which electrode it occurred

(B) calculate the final concentration of nitrate ions in the magnesium nitrate solution

Just to clarify, is it magnesium ion or nitrate ion concentration you want to find?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Nope, this answer is incorrect (was on tapatalk earlier and couldn't see the response). Can any 15ers pick up on what's wrong with this?

This is the problem ive had for a long time i couldnt tell whether it was absolute or negative thanks therefore its -0.34+0.8=0.46

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

This is the problem ive had for a long time i couldnt tell whether it was absolute or negative thanks therefore its -0.34+0.8=0.46

If you don't get why it has to be negative I think you might misunderstand the table of standard potentials. It's a table of standard reduction potentials, you're describing a different, equal but opposite, process when you describe oxidation. It would make no sense at all to use a positive here, because you'd be describing reduction, which isn't the process that's happening.

 

[DepressedPenguino]

re: HSC Chemistry Marathon Archive

This is the problem ive had for a long time i couldnt tell whether it was absolute or negative thanks therefore its -0.34+0.8=0.46

Yeah i got 0.46V too

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Yeah i got 0.46V too

That's the correct answer. I posited that particular question because sometimes people think they have to double the value for Ag when that's not the case. But it didn't catch either of you so well done!

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

How is technetium 99m used in industry ?2marks

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

How is technetium 99m used in industry ?2marks

1. The HSC will never specify Tc-99m as the isotope you're required to write about. You have a choice of industrial/medical isotopes to study.

2. Tc-99m is an isotope used overwhelmingly in medicine, it's not really used in industry. So it's placement in this question doesn't make much sense.

A question like: outline the use of one radioactive isotope of your own choosing in industry (3 marks) conforms much better to the HSC syllabus. I really suggest you start familiarising yourself with the structure of HSC questions so you'll know what to expect.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

1. The HSC will never specify Tc-99m as the isotope you're required to write about. You have a choice of industrial/medical isotopes to study.

2. Tc-99m is an isotope used overwhelmingly in medicine, it's not really used in industry. So it's placement in this question doesn't make much sense.

A question like: outline the use of one radioactive isotope of your own choosing in industry (3 marks) conforms much better to the HSC syllabus. I really suggest you start familiarising yourself with the structure of HSC questions so you'll know what to expect.

Im doing technitium and dont know whata in it for industry

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Im doing technitium and dont know whata in it for industry

You need to have a medical and an industrial isotope. Technetium-99m is great for medical, you'll need another for industry (cobalt-60 is good, plenty of uses and easy to find information on).

 

[zhertec]

re: HSC Chemistry Marathon Archive

Dr Soccerball, I think it'd be better for everyone here's sake if question were rather collected from past exam papers than made up on the spot. This way it gives everyone (including yourself) to experience the type of questions that are going to be presented in the real HSC, compared to questions that are never going to be asked e.g. that use of natural log to calculate pH...

 

[Fizzy_Cyst]

re: HSC Chemistry Marathon Archive

Just to clarify, is it magnesium ion or nitrate ion concentration you want to find?

Nitrate ions its one extra step

 

[strawberrye]

re: HSC Chemistry Marathon Archive

Dr Soccerball, I think it'd be better for everyone here's sake if question were rather collected from past exam papers than made up on the spot. This way it gives everyone (including yourself) to experience the type of questions that are going to be presented in the real HSC, compared to questions that are never going to be asked e.g. that use of natural log to calculate pH...

You do need to use natural log to calculate pH though...and calculation of pH questions are in exam paper.

EDIT: You don't need to use natural log-temporary confusion over maths terminology.