CHEM 5 JUNE 12 Section A Unofficial Mark Scheme

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was it define electronegativity or electron affinity? I swear it was negativity- I wrote the ability of an electron to withdraw electron density to itself in a covalent bond..

I put the definition of standard enthalpy of blah blah electron affinity. I think thats wrong and you are correct though

Reply 21

m1a1tank

Original post by authentic

was it define electronegativity or electron affinity? I swear it was negativity- I wrote the ability of an electron to withdraw electron density to itself in a covalent bond..

sorry mate but im pretty sure it said to define electron affinity

(edited 11 years ago)

Reply 22

simaframe

Original post by authentic

was it define electronegativity or electron affinity? I swear it was negativity- I wrote the ability of an electron to withdraw electron density to itself in a covalent bond..

Im pretty sure it was electronegativity, that's the definition I gave anyway

Reply 23

simaframe

Did anyone else get Zn for the weakest oxidising agent or am I the only one?

I got CdO(OH)

Original post by Yosemite80

doesnt Cr dissolve in xs OH-, so would go to Cr(OH)6^3-?
going by this MS i think i got about 80/100 :/

have u got the paper?

any gt the paper???

Original post by simaframe

Did anyone else get Zn for the weakest oxidising agent or am I the only one?

I put Zn , I dont know why other people said cd ? Zn had the lowest emf value though at like -0.88 , cd was -0.66 or something

Reply 28

blueqq

Original post by m1a1tank

On 3c) where you lot got 794K, i think i got -794K because i think the entropy or enthalpy, can't remember which one, i got it as -70.5.

Did anyone else get this?

gt 2 positive value for enthalpy n entropy...so the temp was positive,,,most ppl in our class gt tht too :confused:

Reply 29

joeeeee

I'm pretty sure it was electron affinity aswell.

Reply 30

dansp175

Original post by m1a1tank

On 3c) where you lot got 794K, i think i got -794K because i think the entropy or enthalpy, can't remember which one, i got it as -70.5.

Did anyone else get this?

There's no such thing as a negative value of temperature in Kelvin.

Reply 31

TheBigDog

Original post by Polioz

I put Zn , I dont know why other people said cd ? Zn had the lowest emf value though at like -0.88 , cd was -0.66 or something

It was definitely the top left compound that was the weakest oxidizing agent. It was more negative at the top and the strongest oxidizing agent is always on the left hand side of the most negative, so the weakest oxidizing agent will be on the left of the most positive.

Reply 32

aljabiraa

Original post by TheBigDog

they weren't in order. i put Zn too as it was the right hand compound in the most negative reaction

Reply 33

m1a1tank

Original post by dansp175

There's no such thing as a negative value of temperature in Kelvin.

thats a good point. That takes the piss :'(

how many marks was that question?

Reply 34

blueqq

Original post by m1a1tank

thats a good point. That takes the piss :'(

how many marks was that question?

prbly 2 or 3

Reply 35

alan-93

Original post by Yosemite80

one of dH or dS was 70.5 but forgot sign... might have been negative
2b units 0.1kJmol^-1K^-1 or 100JK^-1mol^-1, as the axes were in kJmol^-1
my guess for 1d is 3MgO+2H3PO4->Mg3(PO4)2+3H2O, only one which made some sense...
3e is 2NO, they asked for nitrogen monoxide i think

it was positive.
remember gradient was positive so the S is positive as well!

Reply 36

TheBigDog

Original post by aljabiraa

they weren't in order. i put Zn too as it was the right hand compound in the most negative reaction

The oxidising agent is always on the left, because its being reduced.

Reply 37

alan-93

the enropy was 97.7
you had to work out dy/dx.
G was in KJ so you had to convert it into J.
I used y=43KJ and 0 and so x was 900 and 460
so dy/dx=(43000-0)/(900-460)=+97.7JK-1mol-1
and yh it was postive because the gradient was positive!

Reply 38

blueqq

wht did everyone put for carbon neutral qustn...cnt rebmr how it was wordered

Reply 39

s4n4iqb4l

Can anyone remember the potassium titration?
itwas something like work out percentage by mass....
i got 75% i think...but it just seemed so high...probably wrong??