Aqa chem 4/ chem 5 june 2016 thread

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Reply 1960

Can someone explain to me why hydrogen cell is on the left hand side in conventional cell representation(this is my wrong answer).

I thought more negative Electrode potentials are on the left of cell representation?

Reply 1961

Suits101

Original post by Engineerrookie

You are right, HOWEVER, when using SHE it is always on the left (IUPAC rules)

Reply 1962

Super199

Original post by 26december

What do you need explaining?

It's just using the equation:
Delta G = Delta H - T(Delta S)

so when Delta G = 0,
T = Delta H/Delta S

Posted from TSR Mobile

Delta is products - reactants right? Why we halving O2?

2H2 + O2 -> 2H2O
Do the coefficients matter?

cus products -reactants : 2(189) - 2(131) -2(105)

so idk

Reply 1963

Suits101

Original post by Bloom77

But one mole becomes two moles in atomisation, not affinity

Posted from TSR Mobile

When you atomise it, you get 2F.

When you do electron affinity you the have to do it for both F atoms hence 2 X value

(edited 7 years ago)

Reply 1964

zombaldia

Original post by Suits101

You don't know how much that's cleared something up for me...

I always did:

E cell = E RHS - E LHS
= reduction - oxidation
= cathode - anode

And now:
= positive electrode - negative electrode

A lot of chemistry is just trying to simplify it. At least for me anyway. Try use notes on chemrevise for chem5 if you would like some good notes

Reply 1965

SirRaza97

Original post by ss3128593

does anyone know how to do calculation 8C for june 13 paper chem 5
thank you

Reply 1966

jammypancake

Anyone know how to rearrange the equation if they ask you to work out the hydration enthalpy and you have enthalpy of sol already?

Reply 1967

Ejsjwwj

How do you generally do those 5 mark calculation questions

Reply 1968

flylikeafly

Does anyone know if all the oxides form a protective insoluble layer or is it just MgO and Al2O3

Reply 1969

ninjaduck

Original post by SirRaza97

It's 1:2.9, not 1:3. The reason for that is the next part of the question

Reply 1970

thenextchemist

What's the oxidation state of cobalt in this

ImageUploadedByStudent Room1466526474.262787.jpg

I seem to be getting +2 but the answers +3

I did:
Co + 1 - 4 = -1
Co = + 2

Posted from TSR Mobile

Reply 1971

Suits101

Original post by zombaldia

A lot of chemistry is just trying to simplify it. At least for me anyway. Try use notes on chemrevise for chem5 if you would like some good notes

It's where I wrote my notes up from (along with AQA textbook) - I must've missed that! Thanks :smile:

Reply 1972

SirRaza97

Original post by ninjaduck

It's 1:2.9, not 1:3. The reason for that is the next part of the question

Well that's kinda stupid. Oh well 1:2.9 then

Reply 1973

bat_man

Original post by Bloom77

What's the oxidation state of cobalt in this

ImageUploadedByStudent Room1466526474.262787.jpg

I seem to be getting +2 but the answers +3

I did:
Co + 1 - 4 = -1
Co = + 2

Posted from TSR Mobile

think about the overall charge. Its (CoO2)- oxygen has an oxidation state of -2. 2 times -2 = -4.

therefore cobalt has to be+3, as -4+3 = -1

Reply 1974

Suits101

Original post by flylikeafly

Does anyone know if all the oxides form a protective insoluble layer or is it just MgO and Al2O3

I would've guessed all of them, however you only need to know Al2O3 (MgO is given in questions)

Reply 1975

SirRaza97

Original post by Bloom77

What's the oxidation state of cobalt in this

ImageUploadedByStudent Room1466526474.262787.jpg

I seem to be getting +2 but the answers +3

I did:
Co + 1 - 4 = -1
Co = + 2

Posted from TSR Mobile

You only need to look at the compund in the square brackets :smile:

Oxygens = -4 and to get -1 overall charge it's +3

Reply 1976

zombaldia

Original post by jammypancake

Anyone know how to rearrange the equation if they ask you to work out the hydration enthalpy and you have enthalpy of sol already?

Depends if you're giving lattice formation or dissociation. I always draw it out but this is how you do it if given dissociation.

sol=dissociation+hydration enthalpies

simply rearrange to get hydration=sol-dissociatiation-other hydration you are given