* Chemistry * Predictions / discussion / aftermath * (1 thread please)

BeanbagBallbag

http://www.youtube.com/watch?v=zGM-wSKFBpo

resistantdoor

If anyone has the Understanding Chemistry book could you please explain to me what in the snot is happening on page 216 example 12.11?

Exothermic

Being in excess/limiting reagent has nothing to do with where it's it, whether it be the flask or the dropping funnel.
You've made up your solutions so that one is in excess and the other is the limiting reagent.

Think this way:
Sodium dichromate is in excess when oxidising to ethanoic acid. This is because you're going from ethanol to ethanal to ethanoic acid. You don't want to run out of the sodium dichromate otherwise the oxidation will stop. Hence, you've got it in excess you you can do the full oxidation.

BeanbagBallbag

resistantdoor wrote: »

If anyone has the Understanding Chemistry book could you please explain to me what in the snot is happening on page 216 example 12.11?

M1V1/n1 = M2V2/n2 is all it is ,1 mole of potassium manganate(VII) requires 5 moles of ammonium iron(II) sulfate, so n1=1 n2=5 etc

Gavarn

resistantdoor wrote: »

If anyone has the Understanding Chemistry book could you please explain to me what in the snot is happening on page 216 example 12.11?

It's there weird way of doing this:

M1 x V1 x M2 x V2
n1...............n2

They are just cross multiplying, skipping a step.

Hope this helps?

resistantdoor

BeanbagBallbag wrote: »

M1V1/n1 = M2V2/n2 is all it is ,1 mole of potassium manganate(VII) requires 5 moles of ammonium iron(II) sulfate, so n1=1 n2=5 etc

Ok I just had a major brain fart trying to figure out how they decided what to use for n. Better now than tomorrow I guess

Exothermic

Guys, if you're on the computer not up to much I'd suggest youtubing videos on atomic theory or whatevs. You might be able to find a particular experiment too.
I'm finding it much easier to remember things that way rather than trying to remember that Chadwick discovered neutrons, and Thompson with the electrons by rote learning.

BeanbagBallbag

Exothermic wrote: »

Guys, if you're on the computer not up to much I'd suggest youtubing videos on atomic theory or whatevs. You might be able to find a particular experiment too.
I'm finding it much easier to remember things that way rather than trying to remember that Chadwick discovered neutrons, and Thompson with the electrons by rote learning.

I suggested ichemistry.ie a few pages back don't think anyone bothered with it :pac:

Gavarn

http://www.youtube.com/watch?v=JwdGFZA3WOs&feature=related

Get you into a good mood for some FUN chemistry study

macskanadrag

Gavarn wrote: »

http://www.youtube.com/watch?v=JwdGFZA3WOs&feature=related

Get you into a good mood for some FUN chemistry study

I was wondering how i could sleep tonight - this guy is the answer!
Also, i haven't seen a cathode ray before so thanks

nommm

Gavarn wrote: »

"A primary alcohol can be oxidised to a carboxylic acid by refluxing with sodium dichromate solution that is acidified with sulphuric acid" so it must have to be acidified for some reason

It's to stop the Sodium Dichromate being oxidised by the water as far as I can remember.

Exothermic

Gavarn wrote: »

http://www.youtube.com/watch?v=JwdGFZA3WOs&feature=related

Get you into a good mood for some FUN chemistry study

There's a comment saying "Voice reminds me of Kip from Napoleon Dynamite."
... I lol'd. Big time :P

captainkrusty

Is there any point revising the experiments that came up last year or should I just concentrate on the ones that haven't or are predicted. Cause if prep of soap comes up someone is getting beat

Farmer poet

Hey, does ammonium oxalate show the presence of calcium?

Gavarn

captainkrusty wrote: »

Is there any point revising the experiments that came up last year or should I just concentrate on the ones that haven't or are predicted. Cause if prep of soap comes up someone is getting beat

With the way the exams have been going this year, I'd revise them all! Hope soap doesn't come up! Not too keen on bleach either though!

You can take the risk and go with ones that were predicted. But I wouldn't advise it!

Good luck tomorrow

partyatmygaff

Is the Ammonium Iron(II) sulfate standardisation experiment likely to come up? I doubt it but even so...

jumpguy

partyatmygaff wrote: »

Is the Ammonium Iron(II) sulfate standardisation experiment likely to come up? I doubt it but even so...

Nah, although they could ask what primary standard you standardised the KMnO4 against or something, hence a good knowledge of all the titrations is useful.

Anyway, I should be in bed. The LC ain't over yet. (Although close, so, so close )

nitromaster

Anyone got a list of predictions for the experiments?

Dongl

"A primary alcohol can be oxidised to a carboxylic acid by refluxing with sodium dichromate solution that is acidified with sulphuric acid" so it must have to be acidified for some reason

I'm pretty sure the reaction just required H+ ions and sulphuricc acid is the way to get them without having Cl-'s ****ing everything up.

doctorg

anyone know if there are any other formulas in the log table other than page 64

doctorg

Also, Can we use the Mathematical formula for the definitions of the gas laws?

EmacB

EmacB wrote: »

So glad i remembered to ask this..
When they specifically state the number of points for you to make in an answer, do you lose marks for stating more then that amount?
For example if a question says "give two differences between a nuclear and chemical reaction' and you go and put 3 or 4 differences do do you lose marks?
Or what if you put 2 right ones down and a wrong one will you still get full marks?

Just wondering because sometimes id know a few points but not be completely certain if they were all right so id like to just put them all down.

Anyone have the answer to this . Im definitely going to be wondering about it in the test

macskanadrag

EmacB wrote: »

Anyone have the answer to this . Im definitely going to be wondering about it in the test

Yeah, me too Would the examiner know?

Gavarn

EmacB wrote: »

Anyone have the answer to this . Im definitely going to be wondering about it in the test

1. In many cases only key phrases are given which contain the information and ideas that must appear in the candidate’s answer in order to merit the assigned marks.

2. The descriptions, methods and definitions in the scheme are not exhaustive and alternative valid answers are acceptable.

3. The detail required in any answer is determined by the context and the manner in which the question is asked, and by the number of marks assigned to the answer in the examination paper, and in any instance, therefore, may vary from year to year.

4. The bold text indicates the essential points required in the candidate’s answer.Words, expressions or statements separated by a solidus (/) are alternatives which are equally acceptable. A word or phrase in bold, given in brackets, is an acceptable alternative to the preceding word or phrase. Whilst only key words and phrases are indicated in the marking scheme they must be presented in answers in a correct context if full marks are to be awarded.

5. In general names and formulas of elements and compounds are equally acceptable except in cases where either the name or the formula is specifically asked for in the question. However, in some cases where the name is asked for, the formula may be accepted as an alternative.

6. There is a deduction of one mark for each arithmetical slip made by a candidate in a calculation.

7. Where a candidate has received a modified examination paper under the reasonable accommodations arrangements the marking scheme applied has been modified accordingly.

That is the guidelines that the examiner is to follow from the marking scheme.
Does that answer your question?

Iceuil

^^^ Same question. I always put more than required number of answers, but im afraid that they can get cancelled out

macskanadrag

Gavarn wrote: »

That is the guidelines that the examiner is to follow from the marking scheme.
Does that answer your question?

Nope! I'm looking through older marking schemes too, in case they were clearer but nothing.
In marking schemes, sometimes they add a note "cancellation applies". So maybe only in those cases can your wrong answer cancel the right one?

Exothermic

Pretty sure negative marking applies.
If you're putting down 3-4 points... well, don't. Put down two that you know are correct and explain them fully.

Lets say they ask for two points and you give three but one is wrong, you'll have one of your correct answers cancelled. Look at the question asked and the marks going for it, then answer accordingly.

EmacB

Gavarn wrote: »

That is the guidelines that the examiner is to follow from the marking scheme.
Does that answer your question?

Nope sorry

macskanadrag

This is an example from the Biology Examiners' guidelines:

"Marking Scheme; carbon/ hydrogen/ oxygen/ nitrogen 4(3)
Sample answers:
carbon/ hydrogen/ oxygen/ nitrogen/ calcium – there is a surplus answer, which is incorrect, and which cancels one of the correct answers, therefore the candidate is awarded 3(3) marks."

Same applies to chemistry i guess :-/

Exothermic

I just happened to open up the 2006 marking scheme.

Q9(d)
"Apply cancelling if more than two structures are given. Maximum loss is – 3"

So not for all questions, but when specifically asked for a certain number of points, do that number and only that number. If you're answering more it shows you're not confident enough in your answers being correct I guess.