HSC 2012-2015 Chemistry Marathon (archive) (7 Viewers)

theind1996 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?

Riproot · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Sy123 said:
Fixed. But as far as I know it is impossible for there to be those numerical percentages and it meaning mol%, the Carbon - Hydrogen ratio is too high for it to be mol.

But still! It's the principle of the thing.

(It's gravimetric analysis or something, right?)

Riproot · Dec 29, 2012

re: HSC Chemistry Marathon Archive

theind1996 said:
Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?

The pH 6 one would be one of the tricky ones but the percentage one is fine. I think we did more of that stuff in year 11 though iirc.

Sy123 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

theind1996 said:
Umm just curious coz I'm kinda wtf-ing, but are both of your questions HSC level?

They are both within syllabus standards not sure what you mean by HSC level.

theind1996 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Riproot said:
The pH 6 one would be one of the tricky ones but the percentage one is fine. I think we did more of that stuff in year 11 though iirc.

Oh yeah shit.

The empirical formula is from moles shit in Yr 11.

Post some more Production questions guys? I think most people haven't done Acidic in great depth.

Sy123 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

theind1996 said:
Oh yeah shit.

The empirical formula is from moles shit in Yr 11.

Post some more Production questions guys? I think most people haven't done Acidic in great depth.

Yeah, I'll post from Module 1 moreso then next time when I need to ask a question.

HeroicPandas · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Sy123 said:
I would tell you why this is not the case, but it would give the answer away haha.

EDIT: I didn't want to kill the thread this early, here is another question in the mean time while people think about it

Upon analysis of mass of a hydrocarbon was found to contain 82.6% Carbon and 17.4% Hydrogen. Calculate its empirical formula

been a while... isnt this preliminary?

C:H

82.6 : 17.4

82.6/12.01 : 17.4/1.008 (Divide by respective atomic masses)

6.87760... : 17.26170...

dIVIDE both sides by 6.87760

1: 2.5

Times both sides by 2

2:5

THerefore EF: $C_2 H_5$

yeh? or am i wrong

Sy123 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

HeroicPandas said:
been a while... isnt this preliminary?

C:H

82.6 : 17.4

82.6/12.01 : 17.4/1.008 (Divide by respective atomic masses)

6.87760... : 17.26170...

dIVIDE both sides by 6.87760

1: 2.5

Times both sides by 2

2:5

THerefore EF: $C_2 H_5$

yeh? or am i wrong

Correct. Now its your turn to post a question (or anyone else can)

bleakarcher · Dec 29, 2012

re: HSC Chemistry Marathon Archive

HeroicPandas said:
been a while... isnt this preliminary?

C:H

82.6 : 17.4

82.6/12.01 : 17.4/1.008 (Divide by respective atomic masses)

6.87760... : 17.26170...

dIVIDE both sides by 6.87760

1: 2.5

Times both sides by 2

2:5

THerefore EF: $C_2 H_5$

yeh? or am i wrong

I got that too.

RealiseNothing · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Sy123 said:
How is it possible to have NEUTRAL water at ph6?

(just brief and straight to the point)

Something about disassociation, idk exactly since I haven't really started acidic yet.

HeroicPandas · Dec 29, 2012

re: HSC Chemistry Marathon Archive

What is the catalyst used in catalytic cracking?

AND

a) Identify 3 properties of the catalyst that makes it useful
b) Describe 2 of them in relation to catalyst cracking (ie. why is this property useful for cat cracking?)

I'm sorry if it sounds weird, i dont know how to word questions xD

bleakarcher · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Sy123 said:
$HCl \rightarrow H^+ + Cl^-$

$n(HCl) = CV = 0.1 \cdot 0.005 = 0.0005 \ mol$

There is a one to one ratio between HCl and H+

Hence

$n(H^+)= 0.0005$

$\therefore [H^+]= \frac{0.0005}{0.105} =0.0047...$

We get 0.105 from the Volume of the soln which is 105 ml
We now have conecntration of Hydrogen ions, so we take -log of it

$pH = -\log 0.0047 = 2.32$

I hope I'm right lol

=======================

How is it possible to have NEUTRAL water at ph6?

(just brief and straight to the point)

Maybe this is to do with possible minerals dissolved in the water resulting in an increase in the H+ concentration and thus a decrease in the pH?

bleakarcher · Dec 29, 2012

re: HSC Chemistry Marathon Archive

HeroicPandas said:
What is the catalyst used in catalytic cracking?

AND

a) Identify 3 properties of the catalyst that makes it useful
b) Describe 2 of them in relation to catalyst cracking (ie. why is this property useful for cat cracking?)

Properties of zeolite? Shit.

DamTameNaken · Dec 29, 2012

re: HSC Chemistry Marathon Archive

For Sy's question about the neutral water with a pH of 6
The equilibrium reaction is H3O+ + OH- <--> 2H20
Is it possible that the conditions are favouring the backward reaction and so you get a solution which has more Hydronium (and conversely more hydroxide) ions than usual.
Of course I'm probably totally wrong, but thought I'd give it a shot.

Sy123 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

RealiseNothing said:
Something about disassociation, idk exactly since I haven't really started acidic yet.

Related to that as well, yes.

bleakarcher said:
Maybe this is to do with possible minerals dissolved in the water resulting in an increase in the H+ concentration and thus a decrease in the pH?

We are looking at pure water here

DamTameNaken said:
For Sy's question about the neutral water with a pH of 6
The equilibrium reaction is H3O+ + OH- <--> 2H20
Is it possible that the conditions are favouring the backward reaction and so you get a solution which has more Hydronium (and conversely more hydroxide) ions than usual.
Of course I'm probably totally wrong, but thought I'd give it a shot.

How could the conditions favour the Hydronium ions more?

Riproot · Dec 29, 2012

re: HSC Chemistry Marathon Archive

HeroicPandas said:
been a while... isnt this preliminary?

C:H

82.6 : 17.4

82.6/12.01 : 17.4/1.008 (Divide by respective atomic masses)

6.87760... : 17.26170...

dIVIDE both sides by 6.87760

1: 2.5

Times both sides by 2

2:5

THerefore EF: $C_2 H_5$

yeh? or am i wrong

Okay, I got this too originally, but how does it make any sense!??!

It would have to be a carbocation which isn't in the HSC syllabus.

bleakarcher · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Sy123 said:
How could the conditions favour the Hydronium ions more?

Increasing temperature?

kazemagic · Dec 29, 2012

re: HSC Chemistry Marathon Archive

HeroicPandas said:
been a while... isnt this preliminary?

C:H

82.6 : 17.4

82.6/12.01 : 17.4/1.008 (Divide by respective atomic masses)

6.87760... : 17.26170...

dIVIDE both sides by 6.87760

1: 2.5

Times both sides by 2

2:5

THerefore EF: $C_2 H_5$

yeh? or am i wrong

btw is that important in the HSC?

nightweaver066 · Dec 29, 2012

re: HSC Chemistry Marathon Archive

Riproot said:
Okay, I got this too originally, but how does it make any sense!??!

It would have to be a carbocation which isn't in the HSC syllabus.

It's empirical. Could be $C_4H_{10}$ which makes sense.

HeroicPandas · Dec 29, 2012

re: HSC Chemistry Marathon Archive

bleakarcher said:
Edit: nevermind. you mean hydronium ions more than hydroxide ions.

increase pressure

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