OCR Gateway Chemistry C4C5C6 - 13/06/13

Mutleybm1996

Just remember...

Oxygen + Water + Electrons = Hydroxide Ions

O(2) + 4H(2)O + 4e- = 4OH-

Hydroxide Ions + Hydrogen = Water + Electrons

4OH- + 2H(2) ---> 2H(2)O + 4e-

_

What help do you need with them?

CFC's- why's there a continuous depletion of O(3)?

Reply 301

Mathangi

9

Original post by L'Evil Fish

I think there's a mistake in the CGP book.

Page 93

2. So they are attracted to the negative anode and are reduced to copper atoms....

:lolwut:

Oh yeah! It should just be "negative cathode" I'm pretty sure, that's how it is in the picture.

Failing Chemistry

OP

Original post by benwalters1996

CFC's- why's there a continuous depletion of O(3)?

Because Cl O ¤ (¤ is my radical sign :lol:

) is never used up in the process.

ClO¤ + O(3) ---> 2O(2) + Cl ¤

Cl ¤ + O(3) ---> ClO¤ + O(2)

And it happens repeatedly.

Original post by cameron262

Oh yeah! It should just be "negative cathode" I'm pretty sure, that's how it is in the picture.

silly book

Reply 304

foyzx

last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?

Reply 305

Mutleybm1996

19

Original post by foyzx

last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?

55 will probably be an A* due to the section D, add 5/6 to each 2012 grade boundary i reckon.

Reply 306

AR-13

If i got a b in c123 and an a in c/w, wat mark will i need to get a b overall in tmrws exam?

Posted from TSR Mobile

Reply 307

ryanb97

15

Original post by foyzx

last year the raw marks (out of 60) were 19 for a c, 28 for a b, 37 for a, 46 for a*

which i think are fairly low, do you all think that will be consistent this year, or that the grade boundaries will be higher/lower?

It was out of 75

Spoiler

Reply 308

ryanb97

15

Original post by AR-13

If i got a b in c123 and an a in c/w, wat mark will i need to get a b overall in tmrws exam?

Posted from TSR Mobile

What UMS ???

What mark ???

Reply 309

izzzyyay

can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you

Reply 310

Mutleybm1996

19

Original post by izzzyyay

can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you

hi

this video explains it very nicely:
http://www.youtube.com/watch?v=Np-jOY_EshQ
skip to about 2mins or you'll get bored by his voice -.-

Reply 311

BP_Tranquility

5

Original post by izzzyyay

can someone explain to me why weak acids do not completely ionise in water- i know it's because it's a reversible reaction but i don't really understand? xx thank you

I'll give you an example :smile:

-

The chemical formula for ethanoic acid is CH₃COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H⁺ .

However, the other Hydrogen ions (CH₃COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

CH₃COOH -> CH₃COO^- + H⁺

As you can see there are still 3 Hydrogen atoms that haven't ionised and become positive ions. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

HCl ->H⁺+Cl^-

As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

I'm not sure if this is what you were looking for, but hopefully it should clarify some things...? :biggrin:

(edited 10 years ago)

Reply 312

Mutleybm1996

19

Original post by BP_Tranquility

I'll give you an example :smile:

-

The chemical formula for ethanoic acid is CH₃COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H⁺ .

However, the other Hydrogen ions (CH₃COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

CH₃COOH -> CH₃COO^- + H⁺

As you can see there are still 3 Hydrogen atoms that haven't ionised. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

HCl ->H⁺+Cl^-

As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

I'm not sure if this is what you were looking for, but hopefully it should clarify some things...? :biggrin:

picking up from earlier-where about are you with education? because this all seems quite advanced(or maybe i'm oversimplifying the GCSE :eek:

).

as for weak acids-are the reactions always reversible?

ps-please say you and L'Evil Fish are this good at physics too? :biggrin:

(edited 10 years ago)

Reply 313

izzzyyay

Original post by BP_Tranquility

I'll give you an example :smile:

-

The chemical formula for ethanoic acid is CH₃COOH. The underlined H is the hydrogen atom that becomes an ion in water as it loses an electron, becoming H⁺ .

However, the other Hydrogen ions (CH₃COOH) do not ionise (it's something to do with the bonding between the different elements but don't worry about that) so out of the 4 Hydrogen atoms in the chemical formula, only 1 ionises. Because of this, the concentration of Hydrogen atoms in the acid that ionise is low.

CH₃COOH -> CH₃COO^- + H⁺

As you can see there are still 3 Hydrogen atoms that haven't ionised and become positive ions. An equilibrium mixture is formed (the arrow is supposed to be reversible by the way)

But hydrochloric acid which has the formula HCl, has its single Hydrogen atom ionise in water. Therefore, the concentration of Hydrogen atoms in hydrochloric acid that ionise is high.

HCl ->H⁺+Cl^-

As you can see all of the Hydrogen atoms in HCl ionise, so it is a strong acid.

I'm not sure if this is what you were looking for, but hopefully it should clarify some things...? :biggrin:

thank you so much! xx

Reply 314

BP_Tranquility

5

Original post by benwalters1996

picking up from earlier-where about are you with education? because this all seems quite advanced(or maybe i'm oversimplifying the GCSE :eek:

).

as for weak acids-are the reactions always reversible?

ps-please say you're this good at physics too? :biggrin:

No, I'm still doing GCSE :tongue:

I was here on the forums quite a lot for the biology exams but today, I had some other exams so I was focusing on them rather than chemistry. :smile:

Well, I'm quite interested in science so tend to read around the subject quite a lot in my spare time, but the above was mainly from my revision guide. From my understanding, weak acids are usually reversible due to something about the attractions between the different elements...

I've read somewhere that weak acids form an equilibrium mixture because the ions produced in ethanoic acid when it breaks down into CH₃COO^- and H⁺ are not stable so they have the potential to bond back together and form ethanoic acid again. Hydrochloric acid however breaks down into H⁺ and Cl^- ions which are more stable and prevents an equilibrium to be formed. :cool:

Haha, not sure if I'm as good at physics but it is my favourite science but I guess we'll find out. :biggrin:

(edited 10 years ago)

Reply 315

NatashaG

11

GUYS HELP

you know the fuel cell equations?

my book taught me that in acid conditions

ANODE

H2 + 2OH- - 2e- -> 2H2O

CATHODE

O2 + 2H2O + 4e- -> 4OH-

HOWEVER the specimen mark scheme said

positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-

negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-

WHAT? which one is right!?

Reply 316

L'Evil Fish

OP

18

Original post by NatashaG

GUYS HELP

you know the fuel cell equations?

my book taught me that in acid conditions

ANODE

H2 + 2OH- - 2e- -> 2H2O

CATHODE

O2 + 2H2O + 4e- -> 4OH-

HOWEVER the specimen mark scheme said

positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-

negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-

WHAT? which one is right!?

I learnt:

O(2) + 2H(2)O + 4e- ---> 4OH-
4OH- + 2H(2) ---> 2H(2)O + 4e-

Which overall is:

2H(2) + O(2) ---> 2H(2)O

Reply 317

BP_Tranquility

5

Original post by NatashaG

GUYS HELP

you know the fuel cell equations?

my book taught me that in acid conditions

ANODE

H2 + 2OH- - 2e- -> 2H2O

CATHODE

O2 + 2H2O + 4e- -> 4OH-

HOWEVER the specimen mark scheme said

positive (+ve) electrode: O2 + 2H2O + 4e- -> 4OH-

negative (-ve) electrode: H2 + 2OH- -> 2H2O + 2e-

WHAT? which one is right!?

Well, believe it or not, but I was told that they were both correct! :tongue:

My revision guide says:
negative electrode: 2H₂-->4H⁺ +4e^-
positive electrode: 4H⁺ +4e^- +O₂-->2H₂O

But apparently the different equations are different because they give you the reactions from a different perspective- e.g. your revision guide's reactions may be from positive to negative electrode whilst mine's could be from the negative to positive electrode. I'm not sure how this affects the equations though but this was what I was told. If I were you, I would learn the equations in your revision guide since there's a chance the specimen is wrong :cool:

Reply 318

Mutleybm1996

19

Original post by L'Evil Fish

I learnt:

O(2) + 2H(2)O + 4e- ---> 4OH-
4OH- + 2H(2) ---> 2H(2)O + 4e-

Which overall is:

2H(2) + O(2) ---> 2H(2)O

that's what it says in the revision book :smile:

i wouldn't trust the mark scheme, for Q1 it said 'expected answer:nitrogen' 'additional guidance: Mg is acceptable' which..as far as i know...is wrong?

Reply 319

L'Evil Fish

OP

18

Original post by benwalters1996

that's what it says in the revision book :smile:

i wouldn't trust the mark scheme, for Q1 it said 'expected answer:nitrogen' 'additional guidance: Mg is acceptable' which..as far as i know...is wrong?

fair enough, but the book has mistakes too :h:

OCR Gateway Chemistry C4C5C6 - 13/06/13

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you