HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[hayabusaboston]

re: HSC Chemistry Marathon Archive

What is typical alpha helix and beta sheet torsion angle pair for psi/phi? And is this regular or irregular for the structure given?

 

[Queenroot]

re: HSC Chemistry Marathon Archive

What is typical alpha helix and beta sheet torsion angle pair for psi/phi? And is this regular or irregular for the structure given?

I love this part of monitoring and management

 

[Kaido]

re: HSC Chemistry Marathon Archive

How about you guys where are you up to for everything? I got physics half yearly on friday D:

4u: complex,graphs,poly,conics (1/3 through)
3u: most except motion
phy: barely half-way through motors
chem: just finished titration
eng adv: still on hamlet

lol let me know the questions you guys had after you finish your test!

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

4u: complex,graphs,poly,conics (1/3 through)
3u: most except motion
phy: barely half-way through motors
chem: just finished titration
eng adv: still on hamlet

lol let me know the questions you guys had after you finish your test!

Our teachers an ex mechatronic engineer so he gives good questions that kill us..

 

[Fizzy_Cyst]

re: HSC Chemistry Marathon Archive

That feel when I am only up to Lashitayloers principle

Le Chatlier's Principle*

Le Châtelier's principle**

 

[Crisium]

re: HSC Chemistry Marathon Archive

You just use methyl orange to find the equivalence point right..

As DrSoccerBall said you can't titrate two acids as they will not neutralise

+ The indicator depends on the acid and base combination being used.

e.g. For strong base and weak acid it's phenolphthalein (We added the phenolphthalein to the standard solution of sodium hydroxide which was placed under the burette containing acetic acid (the solution of unknown concentration). Since the phenolphthalein is in a strong basic solution it will start off as purple/pink. We would slowly let the acetic acid drip into the solution while stirring it waiting for the colour to change from purple/pink to colourless, which indicates that it has been neutralised, and hence the end point.)

 

[Fiction]

re: HSC Chemistry Marathon Archive

As DrSoccerBall said you can't titrate two acids as they will not neutralise

+ The indicator depends on the acid and base combination being used.

e.g. For strong base and weak acid it's phenolphthalein (We added the phenolphthalein to the standard solution of sodium hydroxide which was placed under the burette containing acetic acid (the solution of unknown concentration). Since the phenolphthalein is in a strong basic solution it will start off as purple/pink. We would slowly let the acetic acid drip into the solution while stirring it waiting for the colour to change from purple/pink to colourless, which indicates that it has been neutralised, and hence the end point.)

I think you meant ekman DrSoccerball implied you could titrate two acids and use methy orange as the indicator to find the equivalence point.

I've wonder if it's possible to titrate a weak acid with a weak base and how you would go along solving that.

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

I think you meant ekman DrSoccerball implied you could titrate two acids and use methy orange as the indicator to find the equivalence point.

I've wonder if it's possible to titrate a weak acid with a weak base and how you would go along solving that.

possible but hard to discern results from miniscule ph change iirc

 

[SuchSmallHands]

Chemistry marathon 2015

I think you meant ekman DrSoccerball implied you could titrate two acids and use methy orange as the indicator to find the equivalence point.

I've wonder if it's possible to titrate a weak acid with a weak base and how you would go along solving that.

It's been nearly a year since I studied this but I had a similar question at the time. I think the problem ended up being the shape of the titration curve. With a weak acid/weak base titration you get a really gradual decline, not the rapid plummet that we need to judge equivalence point so clearly with common indicators.

 

[Ekman]

re: HSC Chemistry Marathon Archive

I think you meant ekman DrSoccerball implied you could titrate two acids and use methy orange as the indicator to find the equivalence point.

I've wonder if it's possible to titrate a weak acid with a weak base and how you would go along solving that.

Apparently you can but you have to use a pH probe with numerous trials...

 

[sovi]

re: HSC Chemistry Marathon Archive

To balance charge of the cell you are making

 

[Crisium]

re: HSC Chemistry Marathon Archive

To balance charge of the cell you are making

wat

That sounds like an answer to: "What is the role of the salt bridge in a galvanic cell?"

In that case:

The role of the salt bridge is to complete the circuit and to maintain electrical neutrality by keeping the charges in both cells zero by allowing the flow of ions.

Appertaining to this:

Justify the use of potassium nitrate as a salt bridge.

 

[Kaido]

re: HSC Chemistry Marathon Archive

I feel like the salt bridge q. has been asked already
KNO3 contains the K+ and NO3- that do not precipitate in ALL solutions (thus able to maintain electrical neutrality...)
Could also talk about electrical conductivity and migration speed, but dont think thats needed

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I think he saw the first question and posted his solution..

 

[Ton5698]

re: HSC Chemistry Marathon Archive

Help with this please.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Didnt @Ekman make a similar question ?

Anyways lets get this forum started again:
For major researchers, sometimes even global collaboration is needed, give two examples and explain the need for each case. 6 Marks

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Didnt @Ekman make a similar question ?

Anyways lets get this forum started again:
For major researchers, sometimes even global collaboration is needed, give two examples and explain the need for each case. 6 Marks

Funny thing is, you can go on virtually any academics website and you'll find they have research partners all over the world...it's characteristic of research, itself.

 

[Crisium]

re: HSC Chemistry Marathon Archive

From 2007 Knox Trial Paper

Polyethene (polyethylene) is an extremely important polymer, available in two general forms-high density polyethene (HDPE) and low density polyethene (LDPE). Which of the following statements about polyethene is correct?

(A) HDPE is branched and has a lower melting point than LDPE.
(B) HDPE unbranched and has a lower melting point than LDPE.
(C) LDPE is branched and has a lower melting point than HDPE.
(D) LDPE is unbranched and has a higher melting point than HDPE.



is the answer C or D?

LDPE is branched and so the monomers cannot be packed closely together, hence the name "low-density"

It therefore has a lower melting point.

Answer: C

 

[hawkrider]

re: HSC Chemistry Marathon Archive

From 2007 Knox Trial Paper

Polyethene (polyethylene) is an extremely important polymer, available in two general forms-high density polyethene (HDPE) and low density polyethene (LDPE). Which of the following statements about polyethene is correct?

(A) HDPE is branched and has a lower melting point than LDPE.
(B) HDPE unbranched and has a lower melting point than LDPE.
(C) LDPE is branched and has a lower melting point than HDPE.
(D) LDPE is unbranched and has a higher melting point than HDPE.



is the answer C or D?

Defs C

EDIT: got ninja'd by crissy

 

[Crisium]

re: HSC Chemistry Marathon Archive

Defs C

EDIT: got ninja'd by crissy

gg no re