****Leaving Certificate Chemistry [All Levels] Before and After Discussion****

J.b96_

Hopefully they basically photocopied the 2003 paper for Tuesday, easiest by far!

chatterboxxx95

plmko wrote: »

Yeah wouldn't mind one of those and any other mnemonics ye know

Don't have a mnemonic for flame test but mass spec peocesses I remember by Vodka (vaporisation)
Is (ionisation)
A (acceleration)
Strong (seperation)
Drink (detection)

And the treatment of water as silly feckin sean follows chelsea football and then add a p at the end for pH adjustment
I know they're silly but they work for me :pac: :rolleyes:

EoghanIRL

plmko wrote: »

Yeah wouldn't mind one of those and any other mnemonics ye know

Porn
Positive oxidation
Reduction negative

Even if it doesn't come up im writing it down anyways .

MacBizzle

What experiments can come up in question 2 so if the dichromate ones can't come up? Soap, ethene and ethyne? Is that it?

little sis...

MacBizzle wrote: »

What experiments can come up in question 2 so if the dichromate ones can't come up? Soap, ethene and ethyne? Is that it?

Benzoic acid
Steam distillation
Ehhh yeh that's all I can think of.
Still dont get how the dichromate ones can't come up though..going to study it anyway I think.

MacBizzle

little sis... wrote: »

Benzoic acid
Steam distillation
Ehhh yeh that's all I can think of.
Still dont get how the dichromate ones can't come up though..going to study it anyway I think.

Is steam distillation the clove oil one?

As you can see I've left all my study for tonight and tomorrow

EoghanIRL

MacBizzle wrote: »

What experiments can come up in question 2 so if the dichromate ones can't come up? Soap, ethene and ethyne? Is that it?

Stop misleading people !

I've seen so many people say this .
The dichromate questions can still be asked ! Just because the reagents are banned doesn't mean they won't ask them .
They can just tell you the reagents and then ask the questions .

chatterboxxx95

MacBizzle wrote: »

What experiments can come up in question 2 so if the dichromate ones can't come up? Soap, ethene and ethyne? Is that it?

Full list of experiments for q2
Ethene
Ethyne
Ethanal
Ethanoic A
Soap
Clove oil
Chromatography

Q3
Flame test
Anions
Recrystallisation/melting point benzoic a
Rmm of volatile liquid
Heat of reaction
Le chatelier
Redox reactions(halogens as ox/displacement of metals)
Hydrogen peroxide with MnO2
Temp/conc on rate of reaction
Free chlorine
Suspendid/dissolved solids

Q1
Standard sol anhydrous sodium carbonate
Ethanoic a vinegar
Water of crystallisation
Prepare standard amm iron II sulphate and standardise KMnO4
Iron tab
Prepare sodium thiosulphate and standardise by tirtation against liberatied iodine
Bleach
Water hardness
Winkler titration

Julius Seizure

Ross31011 wrote: »

Chemistry is by far my worst subject and I think I could fail. I got 32% higher level in the pre exams. Really worried because I have an awful teacher that I never did anything with. What do you think is the best stuff to study for easy marks or if you just want to pass?

Equilibrium and pH are both nice small topics that often have a full question of their own. Be sure you know how to draw the experiments, there are a lot of marks for drawing an oil refining plant or writing how to do a titration. Do every question 4 for as many years as you can with the marking scheme and exam papers. It's not much but it's manageable

MacBizzle

EoghanIRL wrote: »

Stop misleading people !

I've seen so many people say this .
The dichromate questions can still be asked ! Just because the reagents are banned doesn't mean they won't ask them .
They can just tell you the reagents and then ask the questions .

As the person said earlier, we technically aren't allowed do the experiments so they shouldn't be asked in section A. Makes perfect sense, if we're not allowed do them we can't be expected to answer practical questions on them. Could easily come up in section B but that'll only be theory-based, and worth 5 marks or so.

accountname

The ethanoic acid and ethanal preparation can't be asked, the tests for them and possibly related calculations (limiting reagents etc.) can, simples.

little sis...

accountname wrote: »

The ethanoic acid and ethanal preparation can't be asked, the tests for them and possibly related calculations (limiting reagents etc.) can, simples.

Where is this stated?

MacBizzle

accountname wrote: »

The ethanoic acid and ethanal preparation can't be asked, the tests for them and possibly related calculations (limiting reagents etc.) can, simples.

Yep, this is it exactly.

MacBizzle

little sis... wrote: »

Where is this stated?

They said it at in-service days, the reagents got banned in 2011, which was before we started our chemistry course in 5th year so we shouldn't have done them.

CiaraMT

If they couldn't be asked then why are they still on the course?

rainbowtrout

Here's the circular on LC Chemistry issued in Sept 2013.

http://www.education.ie/en/Circulars-and-Forms/Active-Circulars/cl0047_2013.pdf

Circular 0014/2011 (Discontinued Use of Chemicals – Substances of Very High Concern) informed schools of a number
of substances which have been designated as Substances of Very High Concern by the European Chemicals Agency.
As a result of the ban on the continued use of these substances, three of the mandatory practical activities on the
Leaving Certificate chemistry syllabus could no longer be carried out by students. Since 2011, the theoretical knowledge
of the experimental procedure and outcomes of the mandatory experiments listed in the circular remained as part of the
syllabus, but students were not required to carry out the procedure.

rainbowtrout

CiaraMT wrote: »

If they couldn't be asked then why are they still on the course?

Those experiments are being replaced. There are new experiments replacing them for the 2015 examination.

CiaraMT

So we still need to know the "theoretical knowledge". So does that mean it can be asked? I'm so confuzzled!

Wanderer41

Can anyone help with this question? It's a balancing redox reactions, simple enough, just stuck on this one part.
Question is 2008 10 b) iv).
Balance both equations:
ClO- + I- + H+ -> Cl- + I2 + H20
I2 + S2O3 2- -> I- + S4O6 2-.

Hope you can understand that.
The part I'm stuck on is the second equation, for the S2O3 2- and S4O6 2-.
I have the oxidation numbers as S2(+2) oxidised to S4(+5/2). I was multiplying the S2 by 2 to get the S4 but then I have the number of electrons lost wrong. How many electrons are lost? My first equation was:
S2 - 1/2e -> S4 (multiply the left side by 2 as there are 4 S on the right) to give
2S2 - e -> S4.

I'm obviously wrong with the 1/2 electron thing. Can anyone help with this please? Sorry if it's hard to understand.
Thanks

rainbowtrout

Wanderer41 wrote: »

Can anyone help with this question? It's a balancing redox reactions, simple enough, just stuck on this one part.
Question is 2008 10 b) iv).
Balance both equations:
ClO- + I- + H+ -> Cl- + I2 + H20
I2 + S2O3 2- -> I- + S4O6 2-.

Hope you can understand that.
The part I'm stuck on is the second equation, for the S2O3 2- and S4O6 2-.
I have the oxidation numbers as S2(+2) oxidised to S4(+5/2). I was multiplying the S2 by 2 to get the S4 but then I have the number of electrons lost wrong. How many electrons are lost? My first equation was:
S2 - 1/2e -> S4 (multiply the left side by 2 as there are 4 S on the right) to give
2S2 - e -> S4.

I'm obviously wrong with the 1/2 electron thing. Can anyone help with this please? Sorry if it's hard to understand.
Thanks

No, you are correct


The total charge on the S2O3 2- is a -2 charge

So that's 3(-2) = -6 for the oxygen and that means +4 charge overall for the two sulphurs which means they have a +2 charge each on the LHS


On the RHS S4O6 has a 2- charge on it

So starting with oxygen again

6 oxygens each have a 2- charge = -12 in total
So as there is an overall charge of -2 that means the four sulphurs have +10 charge in total
each of the four sulphurs have a +2.5 charge


So sulphur has a change from +2 to +2.5 which is 0.5 of an election

As an increase in oxidation number is oxidation this would indicate a loss of half an electron (in theory anyway)

As you probably worked out Iodine went from a 0 charge to -1 which was reduction and a gain of 1 electron

So the sulphurs need to lose one electron to make the loss/gain of electrons balanced
To do this you need to double the number of sulphurs on the LHS of the equation



So you need to put a 2 in front of S2O3 to balance the redox part of it and then a 2 in front of I- to make the whole thing balance.

MacBizzle

EoghanIRL wrote: »

You are wrong . Yes we can be expected to do them . They can give you the names of the reactants .
. They wouldn't be on the course otherwise .

No! The whole point is that we're not supposed to have done them for section A because they are dangerous. Giving us the reagents doesn't change that fact. They could come up in section B, but we won't be asked it in a question 2.

booblefoop

MacBizzle wrote: »

No! The whole point is that we're not supposed to have done them for section A because they are dangerous. Giving us the reagents doesn't change that fact. They could come up in section B, but we won't be asked it in a question 2.

And to be honest there's so much controversy surrounding the experiment and whether it'll be asked I wouldn't be surprised if they left it out to avoid the hassle.

EoghanIRL

booblefoop wrote: »

And to be honest there's so much controversy surrounding the experiment and whether it'll be asked I wouldn't be surprised if they left it out to avoid the hassle.

Don't study radiation . It's too dangerous . Wouldn't be surprised if they left it out to avoid the hassle .

AtomicKoala

EoghanIRL wrote: »

Don't study radiation . It's too dangerous . Wouldn't be surprised if they left it out to avoid the hassle .

The point is radiation doesn't come up as an experiment.

We're not going to get asked to label an ethanal preparation apparatus or the colour of sodium dichromate.

flyboy83297

why can't Ethanoic Acid preparation be asked in Section A? I was studying chem on my own since there wasn't enough students for a class in my school, any tips will be helpful!!! thanks : )

MacBizzle

flyboy83297 wrote: »

why can't Ethanoic Acid preparation be asked in Section A? I was studying chem on my own since there wasn't enough students for a class in my school, any tips will be helpful!!! thanks : )

The reagents used are banned so we're not allowed do the experiments involving dichromate in class so it can't come up in section A :P

little sis...

What is it exactly that we need to know about chromotography?

A7XGirl

Can someone please explain how I find the instantaneous rate of a graph?

Julius Seizure

A7XGirl wrote: »

Can someone please explain how I find the instantaneous rate of a graph?

You'll be asked for the instantaneous rate at a certain point. Find that point and draw a tangent to the graph. Then pick two points that line up neatly on your graph paper lines and give them coordinates. Rate is the slope which is (y2-y1)/(x2-x1)

MacBizzle

Julius Seizure wrote: »

You'll be asked for the instantaneous rate at a certain point. Find that point and draw a tangent to the graph. Then pick two points that line up neatly on your graph paper lines and give them coordinates. Rate is the slope which is (y2-y1)/(x2-x1)

Or you can just do rise over run, doesn't really matter.