ocr a f325 revision thread

Scroll to see replies

Reply 2780

_HabibaH_

Original post by EllieN95

does anyone know how to calculate percentage dissociation?

(conjugate base/weak acid) x100 for percentage dissociation

Reply 2781

AyshaK

Original post by _HabibaH_

Could you explain that a bit more please? I'd like to know what you're saying too!

moles = vol of gas/24 dm3

Reply 2782

otrivine

Original post by kevloui

FeO4 2- + 8H+ -----> Fe3+ + 4H20

I'm genuinely stumped.. Theres 2 possibilities going on in my head

this is an A* type question

your left hand side species are correct, but the right side you forgot to put oxygen

try again now and balance, the balancing is so hard

Reply 2783

otrivine

Original post by Dr00n

is it
FeO3^2- + 2H^+ -> Fe^3+ + H2O + O2 + 3e^- ?

Reply 2784

kuku2013

are all indicators weak acids

Reply 2785

alltimeemilyxo

Original post by _HabibaH_

(conjugate base/weak acid) x100 for percentage dissociation

whats percentage dissociation?! :frown:

Reply 2786

KD35

Hey, do we have to know the equation for iron (II) and MnO4?

Reply 2787

otrivine

Original post by AyshaK

moles = vol of gas/24 dm3

can I ask ,when we are given electrode poitential values, how do we know which reaction will take place or not, because I heard the 0.4V is not true ?

Reply 2788

alltimeemilyxo

Original post by kuku2013

are all indicators weak acids

weak acids or weak bases

Reply 2789

alltimeemilyxo

for titration curves does the steep part always start at 25cm^3 of base added? why is this?

Reply 2790

AyshaK

Original post by kevloui

FeO4 2- + 8H+ -----> Fe3+ + 4H20

I'm genuinely stumped.. Theres 2 possibilities going on in my head

i got FeO4 2- + 4H+ ------> Fe3+ + O2 + 2H20 + e-

guessing it's wrong cause i usually get hard questions wrong loool

Reply 2791

eggfriedrice

Original post by otrivine

I am giving you a very hard demanding question,

Aqueous ferrate (VI) ions Fe04 2- decompose in the presence of hydrogen ions, forming Iron(III) ions, oxygen and water. Construct an ionic equation for this reaction

Would it be

2FeO4 2- + 10H+ -> 2Fe 3+ + 3/2 O2 + 5H2O

(edited 10 years ago)

Reply 2792

Theafricanlegend

Original post by AFC_123456789

cool but aren't the lone pairs from the two Nitrogens from NH3?

Does chlorine give LP?

chloride* yes.

Reply 2793

kevloui

Original post by otrivine

this is an A* type question

your left hand side species are correct, but the right side you forgot to put oxygen

try again now and balance, the balancing is so hard

2FeO4 2- + 12H+ -----> 2Fe3+ + 6H20 + O2 ??

Reply 2794

Dr00n

Original post by otrivine

What is it, I can't get it :colondollar:

Reply 2795

AyshaK

Original post by otrivine

can I ask ,when we are given electrode poitential values, how do we know which reaction will take place or not, because I heard the 0.4V is not true ?

Hi
Could you explain that cause I don't understand where the 0.4V came from?

Reply 2796

A-New-Start

Original post by otrivine

Fe is being reduced from 6+ to 3+
whereas Oxygen is oxidised from 2- to 0

Reply 2797

_HabibaH_

Original post by alltimeemilyxo

whats percentage dissociation?! :frown:

It came in one of the papers. Basically it just wants you to calculate how much conjugate base dissociated from the weak acid.

Simple equation = ([conjugate base]/[weak acid])x100 (because we want a percentage).