Hsc Question (1 Viewer)

[xxxcaixxx]

anyone has the answer for 2003HSC Shipwreck,corrosion part...
can anyone give me any info or send email to me
thanx a lot
email:lyysys@hotmail.com

 

[smallcattle]

if you need an answer to a particular question i can help

 

[xxxcaixxx]

q31 (b)(1)and(2)
q31 d(2)
q31 (e)

hehe...many answers i want to know
very very thanx for u

srry for ppl
should be 31 not 32..

 

[helper]

Which elective are you doing?
32 is biochemistry not shipwrecks.

 

[xxxcaixxx]

srry
i typed wrong
31 is

 

[smallcattle]

31d2, you will just need to compare the standard potential of cooper and aluminium to the metal you answered in part 1, eg iron.

plastic wont help prevent corrosion and Fe will still corrode so that one is out

then you compare the reduction potential of copper and aluminium to Fe and see which one is higher than iron, then that will be effective because that metal will become anode and Fe is protected as being cathode.

so obviously aluminium is more effective than copper, the fact that Al is passivating metal adds more effectiveness

 

[lucyinthehole]

by oxidation state, do you mean reduction potential??

 

[smallcattle]

31b2, one factor that will affect the rate of the electrolysis is the concentration of the electrolyte. the more concentrated the electrolyte, the more ions there are to migrate through at a faster rate, thus the greater the rate of the electrolysis

as i havent done this experiment so i cant give you the exact precedure, however i think its pretty straight forward, do 1 electrolysis in one concentration of the electrolysis and record the time it takes to reverse corrosion. then do another electrolysis with increased concentration of the electrolyte, record the time and compare it to the first experienment

 

[smallcattle]

by oxidation state, do you mean reduction potential??

yeh, i think so

the table that you will get in the exam

 

[lucyinthehole]

phew... cos oxidation states are those things you use to figure out whether a reaction is a redox one or not... i've never understood HOW exactly you use them to do that, but i know that you do.... something about change in numbers..... any help anyone?

 

[helper]

While I haven't got answers, it would be worth checking the notes from the marking centre that tell you how it was marked and what the common mistakes were.

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2003exams/pdf_doc/chemistry_er_03.pdf

 

[xxxcaixxx]

k>Na>Ca>Mg>Al>Zn>Fe>Sn>Pb>H>Cu>Hg>Ag>Pt>Au
will they give ur the table for that?
coz I never get it in any exam....anyway..i can remember this table.

 

[helper]

Oxidation States is easiest thought of as the sum of its positive and negative charges. So all atoms have equal so they have an oxidation state of 0

If you have an excess of positive
Eg Fe²⁺ then oxidation state +2
Fe³⁺ then oxidation state of +3

MnO₄^- Has 7 extra - (2 from each O and ends up 1 negative) (X+4*-2=-1 x=+7

 

[helper]

No you need to know the order of reactivity but you can basically work it out from the standard potentials. They are basically in order.

 

[lucyinthehole]

Oxidation States is easiest thought of as the sum of its positive and negative charges. So all atoms have equal so they have an oxidation state of 0

If you have an excess of positive
Eg Fe²⁺ then oxidation state +2
Fe³⁺ then oxidation state of +3

MnO₄^- Has 7 extra - (2 from each O and ends up 1 negative) (X+4*-2=-1 x=+7

and how does this relate to redox reactions?

 

[helper]

When a substance increases it oxidation number it is being oxidised Eg 0 -> +1
When a substance is decreasing its oxidation number it is being reduced Eg 0 -> -1

Easier to just remember:

OILRIG

or

LEO the lion GERs
Then talk about which is being reduced and oxidised and rembering what happens in each case to oxidation numbers.