Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed) Watch

Poll: How pumped up are you for this exam?-(warning)-(bad jokes arene this poll!)
"Titanium-I'm not going to corrode (even at high temperatures)" (A*) (22)
16.67%
"Benzene's my middle name, give me the paper in a week and I'll ace it!" (A) (27)
20.45%
"Yeah, I'm fairly electrophillic (positively charged) about the exam" (B) (27)
20.45%
"I'm in the middle of the salt bridge, but I will pass-eventually" (C) (21)
15.91%
"I'm feeling rather electroNegative about this exam" (D) (18)
13.64%
"Benzene, what's that?" (E) (6)
4.55%
"Chemistry, what's that?" (F) (11)
8.33%
This discussion is closed.
jojo1995
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(Original post by Mollymod)
Yeah I made it up off the top of my head for the sake of the question but nevermind
lol sorry... I'm a bad explainer
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posthumus
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(Original post by jojo1995)
aww don't worry, im the same ... its the way we learn i guess

no see below

(i) 2VO2+(aq) + 4H+(aq) + Zn(s) ==> 2VO2+(aq) + 2H2O(l) + Zn2+(aq)

EØreaction = EØreduction – EØoxidation = +1.00 – (–0.76) = +1.76V


i got this from : http://www.docbrown.info/page07/transition03V.htm


"Zinc can reduce the vanadium through each of these steps to give the vanadium(II) ion." - from chem guide --=- i think this means that you would add zinc after each stage, you wouldnt do it all together at once... youd have to do each stage individually, one after another
Ah yes I forgot you don't change those because its STANDARD thankss!!!

Okay now onto zinc... could you tell me if I'm on the right lines here please :

okay so first the Zinc will reduce VO2+...
VO2+ + 2H+ + e- <----------> VO^2+ + H2O
Zn <----> Zn^2+ + 2e-

Now by multiplying the top equation I can now sub in the bottom half equation

2VO2+ + 4H+ + Zn <----------> 2VO^2+ + Zn^2+ + 2H20

Okay the fun doesn't stop there because some excess zinc (reactant) goes right at the VO^2+

VO^2+ + 2H+ + 2e- <----------> V^2+ + H2O

Zn <----> Zn^2+ + 2e-

Now do the same funky subbing stuff to get:

VO^2+ + 2H+ + Zn <----------> V^2+ + Zn^2+ + H20


Now I can add the 2 full equations that are in bold ???
2VO2+ + 6H+ + 2Zn <----------> VO^2+ + V^2+ + 2Zn^2+ + 3H20


Is this how Zinc reduces it.... I'm not too sure about getting the final ultimate full equation though It looks like a right mess


Also I find the fact that Zn gives 2 electrons away from its full & stable 4s orbital... but if it does, the 3d has similar energy orbital, so why not that give some electrons away too? But I guess that's a totally different issue
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jojo1995
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(Original post by posthumus)
Ah yes I forgot you don't change those because its STANDARD thankss!!!

Okay now onto zinc... could you tell me if I'm on the right lines here please :

okay so first the Zinc will reduce VO2+...
VO2+ + 2H+ + e- <----------> VO^2+ + H2O
Zn <----> Zn^2+ + 2e-

Now by multiplying the top equation I can now sub in the bottom half equation

2VO2+ + 4H+ + Zn <----------> 2VO^2+ + Zn^2+ + 2H20

Okay the fun doesn't stop there because some excess zinc (reactant) goes right at the VO^2+

VO^2+ + 2H+ + 2e- <----------> V^2+ + H2O

Zn <----> Zn^2+ + 2e-

Now do the same funky subbing stuff to get:

VO^2+ + 2H+ + Zn <----------> V^2+ + Zn^2+ + H20


Now I can add the 2 full equations that are in bold ???
2VO2+ + 6H+ + 2Zn <----------> VO^2+ + V^2+ + 2Zn^2+ + 3H20


Is this how Zinc reduces it.... I'm not too sure about getting the final ultimate full equation though It looks like a right mess


Also I find the fact that Zn gives 2 electrons away from its full & stable 4s orbital... but if it does, the 3d has similar energy orbital, so why not that give some electrons away too? But I guess that's a totally different issue

the first equation is perfect but you accidentally did v4+(vo2+ -> v2+)... you were meant to do v4+->v3+
then v3+-> v2+ so:


2VO2+ + Zn(s) + 4H+ (aq)


2V3+ (aq) + Zn2+ (aq) + 2H2O (l)


but other than ...i got : for my overall

2VO2+(aq) + 8H+(aq) + 3Zn(s)--- 2V2+ + 3Zn2+ (aq) + 4H2O (l)

look at the equations in the link below and see if you get the same : TELL ME PLS AM I RIGHT OR WRONG ?

http://www.rod.beavon.clara.net/incat9.htm

the first equation in the link doesnt relate to zinc
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posthumus
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(Original post by jojo1995)
the first equation is perfect but you accidentally did v4+(vo2+ -> v2+)... you were meant to do v4+->v3+
then v3+-> v2+ so:


2VO2+ + Zn(s) + 4H+ (aq)


2V3+ (aq) + Zn2+ (aq) + 2H2O (l)


but other than ...i got : for my overall

2VO2+(aq) + 8H+(aq) + 3Zn(s)--- 2V2+ + 3Zn2+ (aq) + 4H2O (l)

look at the equations in the link below and see if you get the same : TELL ME PLS AM I RIGHT OR WRONG ?

http://www.rod.beavon.clara.net/incat9.htm

the first equation in the link doesnt relate to zinc
I see... Zinc does it in 3 steps not 2 !!! That makes sense now

Thank you !

& yup that looks right How do we know exactly not to include H+ in the third step? Or is that something I'll just need to remember because there is no Oxygen anywhere it isn't needed ?
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sounique
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I'm so stuck guys! I'm really struggling with Unit 5 and desperately need an A* in Chemistry for Bham! I just felt so much more confident last year, I don't know what has happened this year. Can anyone suggest any tips on where to get started. Also, has anyone found that there are so many mistakes in the Edexcel book or are is it flaws in my understanding?
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jojo1995
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(Original post by posthumus)
I see... Zinc does it in 3 steps not 2 !!! That makes sense now

Thank you !

& yup that looks right How do we know exactly not to include H+ in the third step? Or is that something I'll just need to remember because there is no Oxygen anywhere it isn't needed ?
I remember it in a way that since there is no oxygen, water isn't formed do no h+ included in the equation ... But remember Hcl is a reagent ... Just remember both Hcl and zinc are used- not sure why ... I think it's the source of the h+ for the first couple of steps but not sure why it's in the last step too ---- PlS CAN anyone CONFIRM THIS !!!!!
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jojo1995
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(Original post by posthumus)
I see... Zinc does it in 3 steps not 2 !!! That makes sense now

Thank you !

& yup that looks right How do we know exactly not to include H+ in the third step? Or is that something I'll just need to remember because there is no Oxygen anywhere it isn't needed ?
Hi there, stay positive and confident ... I'm going to bed now - I'll try help In the m

I remember it in a way that since there is no oxygen, water isn't formed do no h+ included in the equation ... But remember Hcl is a reagent ... Just remember both Hcl and zinc are used- not sure why ... I think it's the source of the h+ for the first couple of steps but not sure why it's in the last step too ---- PlS CAN anyone CONFIRM THIS !!!!!

(Original post by sounique)
I'm so stuck guys! I'm really struggling with Unit 5 and desperately need an A* in Chemistry for Bham! I just felt so much more confident last year, I don't know what has happened this year. Can anyone suggest any tips on where to get started. Also, has anyone found that there are so many mistakes in the Edexcel book or are is it flaws in my understanding?
Hi there, try stay positive and confident ... I'm going to bed now but I'll try help in the morning -
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jojo1995
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(Original post by sounique)
I'm so stuck guys! I'm really struggling with Unit 5 and desperately need an A* in Chemistry for Bham! I just felt so much more confident last year, I don't know what has happened this year. Can anyone suggest any tips on where to get started. Also, has anyone found that there are so many mistakes in the Edexcel book or are is it flaws in my understanding?

I'm alright at chemistry:

I tend to go through the syllabus and ensure I an confident with each point

Revise from markschemes but I only do this after ive been given them and tested at school- just so I don't cheat muself and know what level I'm working at - if that makes sense

Use a few books - I use the facer, the edexcel blue book, and I use the revision guide on a lazy day

I remember equations by trying to write them out off by heart and drawing out mechanism.
and lastly i ask for loads of help on here

Another medic I see
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sounique
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(Original post by jojo1995)
I'm alright at chemistry:

I tend to go through the syllabus and ensure I an confident with each point

Revise from markschemes but I only do this after ive been given them and tested at school- just so I don't cheat muself and know what level I'm working at - if that makes sense

Use a few books - I use the facer, the edexcel blue book, and I use the revision guide on a lazy day

I remember equations by trying to write them out off by heart and drawing out mechanism.
and lastly i ask for loads of help on here

Another medic I see
Thanks so much! I did that last year, I'm just finding the content so much more challenging! Can you help me out with a question, but don't know how to attach a picture here so I'll just write it out.

Ammonia, butylamine, phenylamine all form alkaline solutions in water. The order of increasing pH of equimolar solutions is:

Answer from MS
C6H5NH2 < NH3 < CH3CH2CH2CH2NH2

How did they get that answer, couldn't find it anywhere in the textbook and am so lost.

Any help would be greatly appreciated. My chemistry would rather have a nice long break than help me out, and makes us feel bad when we take up 5 minutes of her time outside of class (goes on a rant about how she's so busy, and has marking to do etc etc). It makes me feel really uncomfortable and pushes me to never asking her a question again.
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Mollymod
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(Original post by sounique)
Thanks so much! I did that last year, I'm just finding the content so much more challenging! Can you help me out with a question, but don't know how to attach a picture here so I'll just write it out.

Ammonia, butylamine, phenylamine all form alkaline solutions in water. The order of increasing pH of equimolar solutions is:

Answer from MS
C6H5NH2 < NH3 < CH3CH2CH2CH2NH2

How did they get that answer, couldn't find it anywhere in the textbook and am so lost.

Any help would be greatly appreciated. My chemistry would rather have a nice long break than help me out, and makes us feel bad when we take up 5 minutes of her time outside of class (goes on a rant about how she's so busy, and has marking to do etc etc). It makes me feel really uncomfortable and pushes me to never asking her a question again.
Okay, so the question is about ordering these solutions from least basic to most basic.

To be a base, something needs to have a lone pair, so it can accept a proton. So these are all bases. The first one is phenylamine. Why is phenylamine a weaker base than Ammonia? Because the lone pair on the Nitrogen are feeding into the delocalised pi system of electrons, so it's a very weak base. Ammonia has a lone pair that's exposed so it's a stronger base than phenylamine.

But in butylamine, CH3 groups are known as electron pushing. They aren't electronegative, so they push the electrons away from themselves towards the Nitrogen atom (which is electronegative anyway)
So the lone pair is even more exposed and will more readily gain a proton than Ammonia/Phenylamine.

Hope that makes sense.
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AS01
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(Original post by Mollymod)
Yeah but after using some of them so often, you can probably remember that Glycine is the simplest one, with a H as the R group in it.

Although that's the only one I know thus far XD
Won't bother learning them either really.
haha same I know only glycine
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AS01
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(Original post by David Tennant)
Yeah, Got an offer from Sheffield...Not sure how though!
that's good! Congratulation!!!
So you just need to get the grades which I am sure you can easily get
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sounique
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(Original post by Mollymod)
Okay, so the question is about ordering these solutions from least basic to most basic.

To be a base, something needs to have a lone pair, so it can accept a proton. So these are all bases. The first one is phenylamine. Why is phenylamine a weaker base than Ammonia? Because the lone pair on the Nitrogen are feeding into the delocalised pi system of electrons, so it's a very week base. Ammonia has a lone pair that's exposed so it's a stronger base than phenylamine.

But in butylamine, CH3 groups are known as electron pushing. They aren't electronegative, so they push the electrons away from themselves towards the Nitrogen atom (which is electronegative anyway)
So the lone pair is even more exposed and will more readily gain a proton than Ammonia/Phenylamine.

Hope that makes sense.
Thank you so much! Makes perfect sense!
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JoshL123
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(Original post by David Tennant)
Yeah, Got an offer from Sheffield...Not sure how though!
Well done on the offer from Sheffield!

On another note, I was told today that the E reaction for hydrogen was 0.76 V? How is this true
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David Tennant
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(Original post by JoshL123)
Well done on the offer from Sheffield!

On another note, I was told today that the E reaction for hydrogen was 0.76 V? How is this true
Hey, thanks!...Are you talking about Ecell values?
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David Tennant
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(Original post by AS01)
that's good! Congratulation!!!
So you just need to get the grades which I am sure you can easily get
Thanks As01! I hope you get all the grades you need too and have a great gap year!
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JoshL123
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(Original post by David Tennant)
Hey, thanks!...Are you talking about Ecell values?
Yeah! I thought it was 0.00V. Our teacher gave us this hw a while ago and it had a reaction asking us why Nitrate couldn't reacted (I believe with Iron) to produce hydrogen gas. The reaction actually produces water
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JRP95
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(Original post by JoshL123)
Yeah! I thought it was 0.00V. Our teacher gave us this hw a while ago and it had a reaction asking us why Nitrate couldn't reacted (I believe with Iron) to produce hydrogen gas. The reaction actually produces water
I don't remember that...
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posthumus
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(Original post by JoshL123)
Well done on the offer from Sheffield!

On another note, I was told today that the E reaction for hydrogen was 0.76 V? How is this true
(Original post by David Tennant)
Hey, thanks!...Are you talking about Ecell values?
Are you talking about electrode potentials ? If so then I don't think that's true... it should be 0?

A Calomel electrode is usually used instead of the hydrogen electrode because it is far more easier to use since it consists of mercury in contact with mercury(I)Chloride. This has an Electrode potential of +0.27V

Where did this person get the value from ? To me it looks like the electrode potential of zinc
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LeaX
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Guys, could I be cheeky and ask how you all revise and ifnyou have any tips? I always struggle in chemistry and I'd love to know how many hours you put in and what you spend that time doing haha. That's if you don't mind sharing your secrets of success.
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