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OCR Chemistry A A-Level 4th June 2019 unofficial mark scheme

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Original post by drprval
[Cr(OH)3(H2O)3] (s) : I'm fairly certain chromium doesn't form that ion?


It does, just like you can have many other hydrated compounds, its the same as saying Cr(OH)3•3H2O
It was D
Original post by mupsman2312
I put A for the false statement, as C was correct (OH- does contain 10 electrons). I don't think Mg(OH)2 is used to treat indigestion - more typically MgCl2, MgCO3 and CaCO3.

Actually, I've just checked, and milk of magnesia is actually a suspension of Mg(OH)2, not MgCl2. So which statement was actually incorrect?
What was D?
Original post by daturastramonium
It was D
I put either B or D? I would hedge my bets on D being right
Original post by mupsman2312
I put A for the false statement, as C was correct (OH- does contain 10 electrons). I don't think Mg(OH)2 is used to treat indigestion - more typically MgCl2, MgCO3 and CaCO3.

Actually, I've just checked, and milk of magnesia is actually a suspension of Mg(OH)2, not MgCl2. So which statement was actually incorrect?
(edited 4 years ago)
I said C (only 2 and 3 correct). Cell potential and overall equation were right, but positive electrode half-equation was wrong (It said alkaline, but gave the acidic H+ version).
Original post by MIKESPIKE10
no, pretty sure the overall equation was incorrect, the Ecell was right though
Original post by BenWhitehair017
It does, just like you can have many other hydrated compounds, its the same as saying Cr(OH)3•3H2O


ah whoops haha
Why was kp> 1?
nooo i swear it was B or basically the option that had it neutralises ALKALINE soils - it doesn’t neutralise alkaline soils it neutralises acidic soils ? or did i dream this i acc don’t know anymore
Original post by daturastramonium
It was D
Original post by El9698
Was i the only one who chose the indicator that started with c?


Cresol blue? If that was the one with the pH range of 7.2-9.6, then so did I.
Reply 789
Avatar for Sven8
Sven8
5
It gave enthalpy change of combustion for s and H2 and when reacted with oxygen in the combustion equation it actually is the values for the formation enthalpies

H2 + 1/2O2 = H2O
And S + O2 = SO2
It was then possible to work out the value for the reactant using hesses law where -2x + (2x enthalpy of both products) = enthalpy change of reaction
Original post by darkcrib
Cu(NH3)4Cl2 is octahedral

Found that quite hard, but you had to half the enthalpy of reaction which gave you the enthalpy of combustion of H2S (reaction was 2 mol H2S but enthalpy combustion is for 1 mol hence half). You were given enthalpy of combustion for H2 and S so from there it was just a Hess cycle for H2 + S --> H2S
Original post by mupsman2312
I said C (only 2 and 3 correct). Cell potential and overall equation were right, but positive electrode half-equation was wrong (It said alkaline, but gave the acidic H+ version).


Ahhh that's sneaky, didn't notice it gave the H+ one.
Original post by neevienoo
nooo i swear it was B or basically the option that had it neutralises ALKALINE soils - it doesn’t neutralise alkaline soils it neutralises acidic soils ? or did i dream this i acc don’t know anymore


No I remember it being B as that statement as well
I said that Kp is much greater than one, so equilibrium lies well to the right.
Original post by Anonymous___
Why was kp> 1?
What did everyone put for that questions asking about number of stereoisomers
Yeah for both questions on this type i put “2 and 3” option so C
Original post by MediocreSince01
Ahhh that's sneaky, didn't notice it gave the H+ one.
3. there were two optical and the cis/trans
Original post by Anonymous___
What did everyone put for that questions asking about number of stereoisomers
Okay that's what I put :smile:
3 (one trans, and then two optical cis isomers).
Original post by Anonymous___
What did everyone put for that questions asking about number of stereoisomers
Does anyone remember the formula of the complex?
Original post by mupsman2312
3 (one trans, and then two optical cis isomers).
Also what did people put for that question with the mass and the options were Ch4 and So2 and SO3 and something else

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