Chemistry build up and aftermath

ironclaw

Jeebus wrote: »

You need to know the ratios

You can easily work them out:



Just as an example, this is 2:1

Just cover the right hand side, the coifficents are your N's in your equations, in most cases.

aine-maire

ironclaw wrote: »

You can easily work them out:



Just as an example, this is 2:1

Just cover the right hand side, the coifficents are your N's in your equations, in most cases.

So we're ALWAYS given the relevant equation(s),yeah?

Jeebus

ironclaw wrote: »

You can easily work them out:



Just as an example, this is 2:1

Just cover the right hand side, the coifficents are your N's in your equations, in most cases.

Generally, yeah. Its usually the acid and the base though, rather than the reactant and the product, no ?

I would be scared of trying to work it outmyself for the whole iodide one too, where the ratio is 1:2:5 or something !

Fringe

From all the papers I've seen, they give the equations in the simplest way. It's merely just recognising which one corresponds to which reactant.

OxfordComma

Does anyone by any chance happen to have the results of the three tests on ethanoic acid? They're not in the book!

celtic723

whats the chances of stoichiometry formulas and equations coming up this year? i ****in' hate it.

ayumi

can someone explain oxidation and reduction,I dont understand how to do the equations

monkseyz

if in stoichiometry you are asked for the number of particles, molecules or atoms do you always multiply moles by 6x10^23?
I know you do for particles just not sure about atoms and molecules.

CallMeDoctor

1fahy4 wrote: »

Does anyone by any chance happen to have the results of the three tests on ethanoic acid? They're not in the book!

Hey first of all learn the equations .
1. Colourless to pink is observed in the first one due to the ethanoic acid being neutralised
2. fizzing due to C02
3. fizzing due to H2 :pac:

Cud u help me? In the bleach titration why cant u use hydrochloric acid?
Wat is the purpose of the sulfuric acid?
Tanks !

monkseyz

CallMeDoctor wrote: »

Hey first of all learn the equations .
1. Colourless to pink is observed in the first one due to the ethanoic acid being neutralised
2. fizzing due to C02
3. fizzing due to H2 :pac:

Cud u help me? In the bleach titration why cant u use hydrochloric acid?
Wat is the purpose of the sulfuric acid?
Tanks !

hcl is oxidised from cl- ions to chlorine gas so it's not used. the sulfuric acid provides H+ ions for the reaction to occur.

monkseyz

what is the purpose of the potassium iodide in the bleach exp?

bythewoods

1fahy4 wrote: »

Does anyone by any chance happen to have the results of the three tests on ethanoic acid? They're not in the book!

To investigate the reactions of ethanoic acid?

Yeah.

Sodium Hydroxide:
Ethanoic Acid + Phenolphthalein indicator. Add sodium hydroxide solution with a dropper.
Pink -> colourless.
Forms the salt sodium ethanoate and water:

CH3COOH + NaOH -> CH3COONa + H2O

Sodium Carbonate:
Slap some Sodium carbonate powder in a test tube, add ethanoic acid.
You get a brisk effervescence (Which is CO2)

Sodium ethanoate and water are also formed:
2CH3COOH + Na2CO3 -> 2CH3COONa + CO2 + H2O

Magnesium Metal:
Throw a bit'a magnesium ribbon into a test tube of dilute ethanoic acid.

You get magnesium ethanoate and hydrogen gas:
2CH3COOH + Mg -> (CH3COO)(2)Mg +H2.

Enjoy d00d, hope that all makes sense.
Dear God, I really do.

bythewoods

CallMeDoctor wrote: »

H
Cud u help me? In the bleach titration why cant u use hydrochloric acid?
Wat is the purpose of the sulfuric acid?
Tanks !

You can't use HCL as the Cl- ions would be oxidised to Cl2

The sulfuric acid supplies the H+ ions....

EDIT: I think...

Nihilist21

ayumi wrote: »

can someone explain oxidation and reduction,I dont understand how to do the equations

Oxidation is loss of electrons by an element, and reduction is gain. With regard to the equations, look at the number of electrons being lost/gained by elements (there will be two, one gaining, one losing) and then balance the equation so all the electrons are used up - if that makes sense. Pm me if that didn't solve the problem

Zonda999

Lads could some one please tell me where i'd find a list of what experiments are which, be it titration, organic or other.

Tryin to sort them out but its hard if you dont know which one can come up where:)

aine-maire

Zonda999 wrote: »

Lads could some one please tell me where i'd find a list of what experiments are which, be it titration, organic or other.

Tryin to sort them out but its hard if you dont know which one can come up where:)

But they all come up in section1 regardlessly (except question 1 is always a titration)

The organic ones are all to be found in the chapters on fuels/heats of reactions, families of organic compounds and reactions of organic compounds.

Titrations are mostly in volumetric analysis and volumetric analysis: oxidation/reduction.

Aisling(",)

i cant remember anything at this point

feck

rainbowtrout

Zonda999 wrote: »

Lads could some one please tell me where i'd find a list of what experiments are which, be it titration, organic or other.

Tryin to sort them out but its hard if you dont know which one can come up where:)

Q1 is always Titrations, so if you're working from chemistry live, look at the list of mandatory experiments in the first couple of pages of the book. The experiments in the acids and bases chapter (13), oxidation/reduction (15) and water (20) are the titrations... there are one or two other water ones but obviously they're not titrations.

Q2 is always Organic Chemistry , so any experiment from Ch. 21-23

Q3 is the remaining experiments in the list.


Anything that came up in the last two years is unlikely to be on this year so you could cross them off your list once you have them sorted out.

Richard Cranium

Me neither. I'm also wrecked after physics and accounting today so I didn't get anything worthwhile done when I got home. Thank God the exam isn't until the afternoon!

Piste

I'm going to avoid as much maths as possible. I tried doing a few of the gas questions and kept getting them wrong =/ Looking back over the last few years it looks like ethanal, ethene or ethyne is likely to come up for organic and bleach or iron tablets for titrations so that's what I'm focusing on. I'm hoping nothing too mathsy in the calculations for those experiments comes up. Still have to cram atomic theory, equilibrium and acids/bases and redox tomorrow before the exam.

I really shouldn't be watching Batman...

phasers

Anybody home yet? I think I may have actually passed! (I dropped down :pac: ) and I managed to answer 8 questions properly. I think I at least passed/sneakily hoping for some sort of C

mikeglee

Having done the exam...I have a new found hate for the subject of that which is chemistry.

jen_23

How did ye get on guys. What came up for ye expected unexpected?

Fluorescence

I have no idea how it went.... I thought I'd passed the mock and failed, and thought I'd failed the winter exam but passed.... I answered 8 questions anyway, and at least 3 or 4 of them are kinda waffley....

Fringe

Went very well

Q3 looked very intimidating at the start but was actually pretty easy. Also, bleach didn't come up. Thought experiments was going to be a disaster but they were so easy.

OxfordComma

Happy overall, I think I got my A1

Anyone else do Q.3? That was the most EPIC tests for anions question ever!

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

HQvhs

1fahy4 wrote: »

Happy overall, I think I got my A1

Anyone else do Q.3? That was the most EPIC tests for anions question ever!

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

Yep, yep and yep! Great paper, experiments were a surprise (except ethyne & ethene) but loved them!

Dmullar

Went really well!

Like physics, the experiments were really doable.

Answered all the questions, hoping for an A:D

Waaahhh

1fahy4 wrote: »

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

Yep!! Was looking for a trick in that question but couldn't find any!

That couldn't have gone any better...

And now I'm finished :D
The mention of whiskey in question 8 had me thinking about the next few days...

RayCarley

What a nice paper. So many of the prediced parts actually came up! Like pretty much all of that paper was predicted in some shape or form.

So yeah hopefully got the old A...

Only 3 left, woooo

JSK 252

Waaahhh wrote: »

Yep!! Ws looking for a trick in that question but couldn't find any!

That couldn't have gone any better...

And now I'm finished :D
The mention of whiskey in question 8 had me thinking about the next few days...

The trick is the dilution factor if there is any such thing as a trick! lol

Whiskey lol. What other ****ing substance is there in whiskey except just pure auld ethanol!

Flavouring agent? I mean I have heard the word condiment being used for vinegar being put on chips but wtf? lol Vinegar is nice though.

Lovely the way it led you to getting the 6% w/v.

Did q1,2,3 ( lovely the way you could just tick the salts off ), 4,6,7,8,10 (a) and (c)

arthistory

1fahy4 wrote: »

Happy overall, I think I got my A1

Anyone else do Q.3? That was the most EPIC tests for anions question ever!

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

Yep i got 510 ppm too!!:D

What did you say for problems if water supply pH was out of range from 6-8? I said corrosion of pipes if too low and hard water if too high.

also is nitrates and phosphates the nutrients....and secondary treatment???

Zonda999

That went great. Couldn't have been happier with that really

Q3 was great if you knew it

QueenOfLeon

1fahy4 wrote: »

Happy overall, I think I got my A1

Anyone else do Q.3? That was the most EPIC tests for anions question ever!

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

Yup!!

JSK 252 wrote: »

Did q1,2,3 ( lovely the way you could just tick the salts off ), 4,6,7,8,10 (a) and (c)

I did the exact same qs as you, with q5 as an extra question....i thought it was really nice, the experiments were lovely!

Des23

1fahy4 wrote: »

Also, did anyone else get 510 ppm for the B.O.D of the brewery effluent?

I'm open to correction, but it said they had 5 litres then they used half of it for the first one, which means that the two BOD readings given were for 2.5 litres. So would you not say that 5.1 ppm was used by 2.5 litres then work out for 1 litre then multiply the dilution factor?

I got 204 or 205 for what its worth...

Nihilist21

Very happy with how that went! Did an extra question, which is the first time I think I've ever done that for a Chemistry exam. Hopefully I got my A1 for that, there was only a couple of things I wasn't too sure of which I may check up now - overall it was a sexy paper though. And also, yay Leaving Cert finished!

OxfordComma

Oh yeah, anyone else not do Q.1?? That was a first for me... I completely blanked for part (b)...:eek:

Anyone else get delta H= -10 for the heat of formation?

GA361

JSK 252 wrote: »

The trick is the dilution factor if there is any such thing as a trick! lol

Whiskey lol. What other ****ing substance is there in whiskey except just pure auld ethanol!

Flavouring agent? I mean I have heard the word condiment being used for vinegar being put on chips but wtf? lol Vinegar is nice though.

Lovely the way it led you to getting the 6% w/v.

Did q1,2,3 ( lovely the way you could just tick the salts off ), 4,6,7,8,10 (a) and (c)

For 10 c (iii),did you get 20.19?

monkseyz

i think it was a nice enough paper, got confused witht he anion tests though lol but think i got them right (hopefully)
wat's a use of ethanoic acid the 1 molar quantity one? was it vinegar?

GA361

1fahy4 wrote: »

Oh yeah, anyone else not do Q.1?? That was a first for me... I completely blanked for part (b)...:eek:

Anyone else get delta H= -10 for the heat of formation?

Yeah . . . . I thought i was wrong cos the figure was so low . . . . but it seems it must be right:D

QueenOfLeon

1fahy4 wrote: »

Oh yeah, anyone else not do Q.1?? That was a first for me... I completely blanked for part (b)...:eek:

Anyone else get delta H= -10 for the heat of formation?

GA361 wrote: »

For 10 c (iii),did you get 20.19?

I got the same as both of those....hope we're all right!

Nihilist21

1fahy4 wrote: »

Anyone else get delta H= -10 for the heat of formation?

That's what I got.

Fluorescence

Yep vinegar :P

Argh I hate the anion tests! Everyone seems to love em but they all just become one big fuzzy blur to me :P

I did Qs: 1,2,3,4,5,8,9,10b and c, 11 a and b.. but 11 won't count cause it's just pure crap

smndly

Right-o, heres a couple of my answers for comparison:

Q.1 e (iii) 32.3% iron in the tablets

Q4 f - pH of nitric acid = 1.6

Q6 e - Heat of formation of C4H8 = -10 kj/mol^-1 ??? Bit weird i thought...

Q8 d - 6% (w/v)

Q10 (a) moles of chlorine = 1.5 moles

(c) Relative Mr of neon = 20.19

Q11 a v catalyst does not effect the value of Kc... not sure if that right though!
:pac::pac::pac::pac:

GA361

Des23 wrote: »

I'm open to correction, but it said they had 5 litres then they used half of it for the first one, which means that the two BOD readings given were for 2.5 litres. So would you not say that 5.1 ppm was used by 2.5 litres then work out for 1 litre then multiply the dilution factor?

I got 204 or 205 for what its worth...

But the dilution factor of 100 remains the same. . . . as there is only 25cm in that 2.5L sample

OxfordComma

Des23 wrote: »

I'm open to correction, but it said they had 5 litres then they used half of it for the first one, which means that the two BOD readings given were for 2.5 litres. So would you not say that 5.1 ppm was used by 2.5 litres then work out for 1 litre then multiply the dilution factor?

I got 204 or 205 for what its worth...

That kinda makes sense but it's not the way they do it in the book... Ah well, if I did it wrong I only lost 3 marks anyways! I really don't care all that much at this stage:D

Des23

did everyone remeber to change the sign of the heat of formation at then end as you had to reverse the heat of formation of C4H8 for everything to cancel?

It was 10 or -10 I can't remember..

Waaahhh

GA361 wrote: »

But the dilution factor of 100 remains the same. . . . as there is only 25cm in that 2.5L sample

+1

(I hope so anyway)

OxfordComma

smndly wrote: »

Right-o, heres a couple of my answers for comparison:

Q.1 e (iii) 32.3% iron in the tablets

Q4 f - pH of nitric acid = 1.6

Q6 e - Heat of formation of C4H8 = -10 kj/mol^-1 ??? Bit weird i thought...

Q8 d - 6% (w/v)

Q10 (a) moles of chlorine = 1.5 moles

(c) Relative Mr of neon = 20.19

Q11 a v catalyst does not effect the value of Kc... not sure if that right though!
:pac::pac::pac::pac:

I think I got all of those!! Left out the ****ing units for delta H though:eek:... There goes a few marks...:(

eoins2345

Just wondering did ye get 32.03% for the the percentage by mass of iron in the tablets?
-10 for the heat of formation ting?
BOD of 510?
In q10a did ye get 3 moles and in 10c 2.19?