AQA - Unit 5 - Energetics, Redox and Inorganic Chemistry

Scroll to see replies

Reply 1000

jwest

question 8c) january 2010 paper, can anyone post a solution?

Reply 1001

NRican

Original post by strawberry_cake

i did the jan11 a few weeks ago, not properly, just did a q, marked it, then the next as i had soo much other stuff to do and now have forgotten about it all :frown:

btw can you help me with q 8c from the jan10 paper? I don't know which equations to use to see the ratio of the moles :/

the titrations are annoying, i can do them but never know what to do for the last step when it wants the percentage or something...

And i've just remembered that i still need to go through mod1 after i've been thorugh the syllabus :cry2:

p4o10 + 6h20 ---4h3po4

Reply 1002

choc1234

for jan10 question 3c)
is this correct as its different in the MS:
Pt|OH-|H2|H2O|||O2|H2O|OH-|Pt
with state symbols i know :smile:

thankyouuuu any help appreciated¬!

Reply 1003

alimaahmed

Original post by Rahul_V

when is a reaction feasible or spontaneous?

reaction is feasible when ?s is large a positive, an ?H is negative and ?G Is negative.
that's what we have been taught correct me if i'm wrong :smile:

Reply 1004

NRican

Original post by jwest

question 8c) january 2010 paper, can anyone post a solution?

Credit to Sheldon

http://www.thestudentroom.co.uk/attachment.php?attachmentid=106997&d=1308828134

Reply 1005

alicetalbot

Original post by alimaahmed

reaction is feasible when ?s is large a positive, an ?H is negative and ?G Is negative.
that's what we have been taught correct me if i'm wrong :smile:

when delta G is negative

Reply 1006

strawberry_cake

Original post by NRican

Credit to Sheldon

http://www.thestudentroom.co.uk/attachment.php?attachmentid=106997&d=1308828134

Thank you

Reply 1007

508836

Original post by Mazii

It's an exothermic reaction as delta H is negativee

The markscheme says otherwise :/

Reply 1008

sophiakrywycz

Original post by kabolin

ewds

Reply 1009

-jessica

Original post by jwest

question 8c) january 2010 paper, can anyone post a solution?

The way I did it (not 100% sure if this is the right way!):

Know two equations for P4O10
-P4O10 + 12NaOH -> 4Na3PO4
-P4O10 + 6H2O -> 4H3PO4

moles NaOH = 0.5 x 21.2x10^-3 = 0.0106 mol
From equations, moles H3PO4 = 0.0106/3 = 3.53x10^-3 mol

So moles P4O10 = 1/4 x 3.53x10^-3 = 0.883 mol

Mr of P4O10 = 284

mass = moles x Mr = 0.883 x 284 = 250.9 = 251 kg (3 s.f)

Reply 1010

alicetalbot

Does anyone have the link for the Jan 11 Mark Scheme?

Reply 1011

Willyg11

Original post by alimaahmed

reaction is feasible when ?s is large a positive, an ?H is negative and ?G Is negative.
that's what we have been taught correct me if i'm wrong :smile:

Just delta G negative i think

Reply 1012

cleo101

when do u put pt into the cell diagram?

Reply 1013

OsmosisJones

Original post by sophiakrywycz

any tips on learning colours fast?

Learn all the easy ones:

Fe2+ is generally green
Fe3+ is purple, precitates go brown
Cu2+ is generally blue
Cu and Fe form yellow solution with Cl
Cr3+ is generally green, remember titration, orange goes green, Cr2O7- ->Cr3+
MnO4- is deep purple, Mn2+ is light pink (titration)
Carbonates generally stay the same colour if bonded to 2+ ion, hydroxide formed 3+ ions.

There are others you are required to learn, but these are the easy ones.

Others include:
Co2+ is pink solution, blue prec. in hydroxide, yellow in excess ammonia
Co3+ is yellow, brown in hydroxide
Cr3+ is purple in excess ammonia
Cu2+ only allows 4NH3 around it, deep blue colour.