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Aren't you currently off for Half term? :confused:

Teachers still have to work during Half-Term. So I used it to my advantage to go and see them.

Maths Teacher is in tomorrow, I will use his room to study.
Chemistry Teacher is in on Friday will use his room to study and ask him questions.

The only place success comes before work is in the dictionary.
Vince Lombardi

Reply 1101

MathsNerd1

Original post by Better

Oh I see, none of my teachers are made to go in during the half term as my parent is a teacher to where I go and they can't be gotten a hold of either if any help is needed, so I'm just planning to read through the content of the book, try to past paper questions in the back and then finally move onto past papers under timed conditions to get my time management under control :smile:

Reply 1102

Better

Original post by MathsNerd1

Oh I see well good luck. I should start January 2012 Paper now anyway so catch you guys later.

Reply 1103

Better

Actually just a quick question - does anyone have a faster way to remember the Hydrogen-Oxygen Fuel cell it keeps coming up.

Reply 1104

master y

Original post by Better

Actually just a quick question - does anyone have a faster way to remember the Hydrogen-Oxygen Fuel cell it keeps coming up.

what specific question? They never actually ask you to know what happens at the positive/neg electrode, just the overall equation.

Reply 1105

Better

Original post by master y

what specific question? They never actually ask you to know what happens at the positive/neg electrode, just the overall equation.

Lol.

They asked you for the Actual Equations in June 2011.

At both Half-Cells.

Reply 1106

Gulzar

Original post by Better

Lol.

They asked you for the Actual Equations in June 2011.

At both Half-Cells.

Whaa??? So you have to memorise the complete reaction, thats so annoying!

Reply 1107

CCLK

Am I the only one stressing about this exam?

Reply 1108

otrivine

Original post by CCLK

Am I the only one stressing about this exam?

Not really, everyone is stressed :tongue:

Reply 1109

sc_5

Can anyone please explain the magic tang question?

Reply 1110

CCLK

Original post by Better

Lol.

They asked you for the Actual Equations in June 2011.

At both Half-Cells.

I'm doing that paper now. which question? I can't find it. Maybe it's just too late for me :s-smilie:

. Glad I'm not the only one stressed that conciliation makes me feel a tiny bit better lol. Moaning aside are any of you good with equalibrium constants I'm stuck on Q 2c ii) on June 2011 I've been using the 'ICE box' method but I'm begining to debate whether this approach should be taken with these problems or not. If you have an alternative please do tell. I don't think the book goes into enough detail either by the way.

Reply 1111

master y

Original post by Better

Lol.

They asked you for the Actual Equations in June 2011.

At both Half-Cells.

just memorise the equations then, it doesn't take much brainpower :smile:

Reply 1112

FailedMyExams

Can someone please explain to me what's going on on page 120. The initial rates bit, I don't understand clock reactions, especially how they get 1/t?

Do we just have to memorise that initial rate is proportional to 1/t and not necessarily understand why?

(edited 10 years ago)

Reply 1113

Funtry

Original post by FailedMyExams

clock reactions are timing something sudden - say the formation of iodine or the change in colour of an indicator, whatever - and then changing the initial concentrations of one reactant, whilst keep the others the same to see if there's any change in time. You may also want to check out the disappearing cross experiment, which is used to check for the formation/dissolving of a precipitate. I'm not that great at clock reactions so you may want to double check that.

The '1' takes the place of concentration, so 1/t IS rate. for example, if it takes 20 seconds to form the iodine say, yet of an unknown concentration, then putting 1/20 = rate, will give you a good idea for the rate. As the rate is changing, it doesn't matter what you put above t as such, it will always change by the same ratio (I know what I've said isn't too clear, but hopefully it's enough!).

EDIT: Say for example the iodine is formed in 20 seconds, with an initial [I-] of 0.5M and say [H+] of 1M (I know this isn't a real reaction, as that would form HI, but I can't be arsed to write out thiosulphate), then this would have a rate of 0.05 moldm^-3s^-1. However, if you were to change the [I-] to 1M and keep [H+] at 1M, then the time may change to 5s. This would give a rate of 1/5, or 0.2 moldm^-3s^-1 which is an increase of 4 in the rate (as 0.2/0.05 = 4) and the initial concentration of [I-] only doubled, meaning that the reaction is 2^nd order with respect to I- (as I- has been doubled, and the rate quadrupled, so [I-] is proportional to rate²). Then you can do the same for H+, but this may have no effect, and so the reaction will be zeroth order with respect to H+.

The other way of working out orders etc is concentration time, which measures how the concentration of a reactant/product changes over time. The half life of these reactants (primarily) can either be constant, reducing, or increasing. What they do depends on what order they are.

I know I've gone way off tangent, sorry, but I'm covering all bases :tongue:

(edited 10 years ago)

Reply 1114

Funtry

Original post by CCLK

Am I the only one stressing about this exam?

Nope

Reply 1115

Better

Original post by Funtry

Nope

Funtry is a God though.

Please can someone help explain Redox Reactions to me and Also Molecular Formula etc.

I've done 3 Past Papers and my only mistakes have come from:
1. Things to do with AS-Level Molecular Formula, deriving the Actual formula of something once you work out the Empircal Formula?

2. Multi-step i.e. 3-6 Step Redox Titrations.

Any tips would truly be appreciated. There must be a more generalised and better way to think about approaching these questions. Right now I suck at them.

Reply 1116

MathsNerd1

Original post by Better

Well with a molecular formula I'm sure you're aware of how to derive the empirical formula from AS Level, if not then its the smallest whole number ratio of the atoms of each element in a compound, well once you've got the empirical if you work out the molar mass for that then they also normally provide you with the actual mass of the compound so you just scale the empirical one up until it matches the one provided, this should then give you the molecular formula.

Reply 1117

Better

Original post by MathsNerd1

I see the word Scale-Up kind of made the whole thing kind of click. Thank you I appreciate it.

And if anyone has any ideas for the Second Part. I don't really want to do another Past Paper until I nail REDOX Titrations.

If anyone has any idea where I could get Papers or where I should practice for those questions specifically that would be great? Maybe I should do the End of Chapter Questions again :s-smilie:

Reply 1118

MathsNerd1

Original post by Better

Yeah I just compare the two things and see how to make them the same, I suppose it does help that I have a more mathematical approach to this unit as there is a lot of calculations to do, not saying that you don't but half the things I do I'm unable to explain that well as I just do them and it work out okay. Also what don't you understand about the Redox titrations? Is it with MnO4- and Fe or using Thiosulphate?

Reply 1119

Better

Original post by MathsNerd1

Well that is simple for 1 Equation but you are often told to create Equations for around 3/4 Equations and then go through and Up-Scale the Number of Moles.

Maybe I am making it more complicated than it actually is.