CHEM 5 JUNE 12 Section A Unofficial Mark Scheme

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??

I got 130% using their 3:7 ratio so i wouldn't hedge your bets on your answer being too high :')

Yeh it seems to be the question everyone is in uproar about, well one of many....:'P

did u write ur value down, i ran out of time, decided to use their values, got something similar to you, 30 seconds left thought it was wrong so i left it out, but i swear thats impossible, and then i was told to close my booklet by the invigilators. I know everyones complaining about the exam, but tbh, i do think most of the stuff couldve been done, if solid revision was done, though that was not the case with me, but surely this question should be emitter, WHAT SLY GAME ARE AQA TRYING TO PLAY

This is Section A, obviously loads/most are wrong because I thought this was a ridiculously hard exam, and a lot of it unrelated. I still don’t think boundaries will change too much because AQA aren’t like that, 70 for an A i reckon. Everyone edit and let’s try and come up with a proper mark scheme

Question 1 is 9 marks

1a) Why is Phosporous Oxide stored in water? – Reacts violently in air
b) Why P4O10 not P2O5? – P4O10 is it in its most stable form under standard conditions
c) Equation = P4O10 + 6H2O = 4H3PO4
pH = 0
d) equation for MgO + H3PO4 – No idea
e)Why can you use excess MgO? Because H3PO4 is a strong acid
f) Why is NaOH an environmental risk? Strong alkaline harms fish?

Question 2 is 7 marks
2a) Equation – G = H – TS
b)Gradient = 0.1 Units = J K mol-1 Symbol = S
c) Why is significance of temperatures below the temp line – delta G is negative so reactions are feasible
d) Why does curve slope? – Change of state, freezing.

Question 3 is 10 marks
3a) delta H =
b)Delta S =
c) T = 700 K? Can’t remember the other 2 but they gave this temperature.
d) why would NO2 not form? – Not 700K
e) N2 + O2 = NO2
f) same number of moles so small entropy so small TdeltaS

Question 4 is 12 marks
4a) Define enthalpy of electron affinity – Enthalpy change when 1 mole of electrons added to an isolated atom in the gas phase
b) Why is F- more electronegative – more shells so more and further from nucleus
c) Why does F- have more negative enthalpy of hydration? No idea
d) Calculation – can’t remember I got 900 something I think
e) Why is it always feasible – delta G always negative because entropy positive and enthalpy change is negative?
f) Can’t remember but it was 2 marks

Question 5 (a disgrace) was 17 marks
5a) Weakest oxidising agent – CdO(OH) because it was most negative.
b) emf = 1.1? can’t remember
c) Equation – cant remember
d) Carbon anode – conduct electricity
e) Essential property of porous cover? – Inert
f) Why leakage? Ions used up
g) +3 and reverse equation
h) Environmental problem? More waste/to landfill
Two ethanol (wtf) fuel cell questions
I) Carbon neutral as no net emission into atmosphere as ethanol comes from plants that photosynthesise.

Question 6 was 10 marks
6a) Coordinate bond
b) O atom acts as Lewis base and donates electrons
Metal ion acts as Lewis Acid and accepts electrons.
c) 180 degrees
d) ratio 3:5 and calculation – no idea

Someone else do section B??

have u got the paper?

isnt that the same thing as conducting electricity ?

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

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

it was asking for the best reducing agent in a roundabout way

1. d) 3MgO + 2H3PO4 = Mg3(PO4)2 + 3H2O

Think that's right?

Do you reckon? i'm not sure they were