Chemistry build up and aftermath

RayCarley

Fringe wrote: »

Think they asked a question like this where the number was less than 0.4 and it pretty much ruined the entire question since none of us were exactly sure. My teacher completely went over that and the marking scheme. If it's 0, it's pure covalent. 0 - 0.4, it's slightly polar but it's pretty much negligible so you wouldn't consider it a polar molecule. Over 0.4, it's polar covalent. Over 1.7, it's ionic.

Check out 2007 5(b)... They ask about the type of bond between H and S... that's a difference of 0.4 in electronegativity.
The marking scheme accepted: "weakly polar // almost non-polar // covalent bond "

So yeah it looks like you just have to mention that it's basically non polar, but still is slightly.



Oh yeah and what do people think the odds are that we get a full question on Instrumentation in section B... nothing like that has come up since 2002... I'm trying to learn it anyway.

Does anybody know one piece of experimental evidence for the addition reaction between HCl and C2H4? Is it where you add NaCl to the water, and they form Na+ and Cl- ions in the solution? What does it form?

Thanks.

CallMeDoctor

-JammyDodger- wrote: »

Does anybody know one piece of experimental evidence for the addition reaction between HCl and C2H4? Is it where you add NaCl to the water, and they form Na+ and Cl- ions in the solution? What does it form?

Thanks.

Yea man you got it add NaCl and Bromine/water and it forms 1-bromo-2-chloroethane
Wat u expectin to come up?

QueenOfLeon

-JammyDodger- wrote: »

Does anybody know one piece of experimental evidence for the addition reaction between HCl and C2H4? Is it where you add NaCl to the water, and they form Na+ and Cl- ions in the solution? What does it form?

Thanks.

I think i know the question you're talking about...the one that usually would have evidence involving bromine? But you couldnt say that because it was HCl and not Br2? A teacher who corrects the paper (and is pretty high up in it) was saying that that particular year caused alot of problems for that question, and they were accepting something along the lines of "if this happens in the presence of bromine water and NaCl etc the following products are formed - 1,2-dibromoethane, 1-chloro-2-bromoethane, 2-bromoethanol." which is the expt evidence given in all text books. I'm not sure if that answers your question, but he reckoned it wasnt likely to be asked again in that way because of the confusion it caused....sorry if i havnt explained that properly

Jeebus

-JammyDodger- wrote: »

Does anybody know one piece of experimental evidence for the addition reaction between HCl and C2H4? Is it where you add NaCl to the water, and they form Na+ and Cl- ions in the solution? What does it form?

Thanks.

1-Chloroethane is formed. A cyclic intermediate is not formed in the case of the addition of Cl2 ir HCl to ethene. This is because the Cl atom and the H atom are too small to form a ring compound.

If I was asked that, and I dearly hope we aren't, then I reckon Just saying chloroethane is formed should get you your marks, no ?

almostnever

-JammyDodger- wrote: »

Does anybody know one piece of experimental evidence for the addition reaction between HCl and C2H4? Is it where you add NaCl to the water, and they form Na+ and Cl- ions in the solution? What does it form?

Thanks.

Personally I'd BS about adding water,and how the water molecule attacks the carbonium ion to from 2-bromoethanol,thus proving the existence of the carbonium ion. Not sure if that's strictly correct,but I'd say that question would cause considerable hassle and so marks would be handed out for any piece of valid experimental evidence

....I don't know if that made sense

@Anne-Marie

Thanks guys, yah that explained it perfectly!

@Anne-Marie, yah that's the question alright!

Thanks guys.

almostnever

This is probably a stupid question,but do we need to know the relevant equations re. the sodium hypochlorite titration?

Jeebus

almostnever wrote: »

This is probably a stupid question,but do we need to know the relevant equations re. the sodium hypochlorite titration?

No.

You need to know the ratios, for the titration equations, but you don't need the full formulae, no.

Okay, predictions for tomorrow everyone ?

Q1. Iron/Bleach/Edta
Q2. Ehyne/Ethene
Q3. Rates of reactions experiments/Benzoic acid/anions/pV=nRT
Q4. Short questions, yay ! Boyle's Law. Charlie's law.
Q6. Trends in periodic table
Q6. Organic, anyones guess.
Q7. Mass spec and them.**
Q8. Organic. Anyone's guess.
Q9. Water/Seweage treatment
Q10 Oxidation (part about Conjugate acids and bases), Acids and bases.
Q11. Radioactivity and....something random.

** On the subject of the mass spec and those...thingies, I have a question in front of me : "What are the main principles on which gas chromotography and Mass spectrometry are based?".

Wut ?! Anyone have a clue ?

QueenOfLeon

Jeebus wrote: »

** On the subject of the mass spec and those...thingies, I have a question in front of me : "What are the main principles on which gas chromotography and Mass spectrometry are based?".

Wut ?! Anyone have a clue ?

MS: Positively charged ions moving in a magnetic field are seperated on the basis of their relative masses

GC and HPLC: Seperation of the mixture is based on the different attractions of the components of the mixture for the mobile phase or the stationary phase based on the polarity of the substance

:DYey for good notes!

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...