[2006019]

(Original post by solittletime)
Why was ammonia mixed with petrol? I didn't like the section C ..

and why does calcium nitrate form different products?

I said the ammonia was mixed with petrol so that it was available as a liquid as ammonia has a low boiling point and therefore in standard conditions it would be a gas, again a bit of a guess

I talked about thermal stability and how the calcium ion is more polarising due to 2+ charge compared to 1+ so the bond to the N has greater distortion so is weaker and therefore less energy is required to break it

Hmm, I thought the paper was OK but like with my answers here they were a bit of a stab in the dark

[Lil Monkey]

Got a feeling that the grade boundaries are gonna be really high :/ about 65 / 66

[avipsita]

(Original post by HARVEY123)
Grade boundary prediction ?? I think 58/60 for an A
A

The paper is out of80

[Blob2491]

What did you guys put for how does the titration increase reliability but decrease accuracy?
Also what was with the oxygen isotope question...

[Kysa]

What did you guys put for how does the titration increase reliability but decrease accuracy?
Also what was with the oxygen isotope question...

Splitting the titration sample into four:
-Increases reliability as you can then repeat and take an average.
-But decreases accuracy as you'll get a smaller titrate, and the lower the measurement the higher the percentage error.


For the oxygen isotope one I said that even though there is no change in the concentrations of either product at equillibrium, the reactions are still ongoing at an equal rate, therefore ozone is still being made using the isotopes.

[Buckers]

(Original post by Vocker)
i messed up on that question and started to write that it is a tertiary carbocation and why it is a carbocation. i didnt say anything about its a trignonal planar or anything of that. anyone think i might get like atleast a mark for that?

I also made this mistake, but thought it was a rather unclear question.

Clearly when I wrote my answer I knew that it is referring to shapes as in trigonal planar etc. but I just thought it was a bit strange given all the bonds present in the CH3 groups? Should of just gone with my instinct instead of what I thought was more plausible.

As a whole, I thought that was a relatively easy section A, but C was a bit tricky given it being quite heavy on the "suggest reasons" questions when you never really know exactly what they want.

[sabre2th1]

For the sodium thiosulfate question:

First part you just do concentration x volume = moles
Second part you divide the value obtained in the first part by 2
Third part has the same answer as second part.

Is the above correct?

[Blob2491]

(Original post by Kysa)
Splitting the titration sample into four:
-Increases reliability as you can then repeat and take an average.
-But decreases accuracy as you'll get a smaller titrate, and the lower the measurement the higher the percentage error.


For the oxygen isotope one I said that even though there is no change in the concentrations of either product at equillibrium, the reactions are still ongoing at an equal rate, therefore ozone is still being made using the isotopes.

What were the equations for methane and ammonia combustion?

CH4 -> C + 2h2
Nh3 -> N + 1.5h2

In the passage it says they decompose directly into their constituent elements or something like that

Ahhhhh nitrogen is diatomic :O

[Buckers]

(Original post by sabre2th1)
For the sodium thiosulfate question:

First part you just do concentration x volume = moles
Second part you divide the value obtained in the first part by 2
Third part has the same answer as second part.

Is the above correct?

Indeed that is was I got, went slightly down hill from there though!

[NutterFrutter]

(Original post by Blob2491)
What were the equations for methane and ammonia combustion?

CH4 -> C 2h2
Nh3 -> N + 1.5h2

In the passage it says they decompose directly into their constituent elements or something like that

Nitrogen is a diatomic molecule.

[Kysa]

What were the equations for methane and ammonia combustion?

CH4 -> C 2h2
Nh3 -> N + 1.5h2

In the passage it says they decompose directly into their constituent elements or something like that

Oh god, I'm not sure I remember. Was it asking for the thermal decomposition or for the combustion?
But yeah, the passage was quite nice, it gave almost all the information.

What did anyone say for the question asking what extra info you'd need to compare CH4 and Ammonia as fuels?

I think I put:

CH4 + 2O2 —> CO2 + 2H2O

and

2NH3 + O2 —> N2 + 2H2O

[Blob2491]

(Original post by NutterFrutter)
Nitrogen is a diatomic molecule.

would they give me the marks? usually in the markscheme it says accept multiples/divisions i think?

[Kysa]

Oh, I fail at clarity. The equations were for the combustion question.

For the additional information, I think I made something up about energy density (is that a thing that even exists?) and something along the lines of the cost of extracting the natural gas for the methane.

[NutterFrutter]

(Original post by Blob2491)
would they give me the marks? usually in the markscheme it says accept multiples/divisions i think?

Multiples means moles, you can't just write N for nitrogen, it's N2. So no it wouldn't get the mark.

[Buckers]

(Original post by Blob2491)
would they give me the marks? usually in the markscheme it says accept multiples/divisions i think?

I think that is referring to multiples of the molar ratio. Candidates make great fun of this by having rather unreasonable ratios, for the mere joy of annoying the examiner haha!

[Blob2491]

I'd at least get 1 mark right?
What did you put for the page long isomer Z questions on structural formulae?

[itsmehello]

for multiple choice
A
-kinetic energy
-area under curve doesn't change
-add hexane to aqueous to form puprle layer
-double bond pi bond and sigma
-which option wasn't 2,2 dimethylpropane...First one which was a skeletal formula with OH at the top
-CFC's are not flammable
Can't remember anymore

Section B
Moles in the sample 4.7.. x10^-6
Then for the next part to find it in ppm I put 0.047.. But I think it's wrong, I worked out the moles in 1,000,000 m^3
Increases reliability I put repeats could be taken, mean could be calculated and anomaly could be identified
Decreases in accuracy as less iodide ions oxidised to iodine so less can be titrated, so lower volume of titre which increases % error.

Ozone question
-For the one about when they added a substance and it came up in reactants and products, I said there was dynamic equilibrium concentrations stayed constant but the rate of forward reaction and back were equal, the reactions were still continuing.
-Ozone was used instead of chlorine, chlorine produces free radicals, ozone produces a harmless biproduct of O2..
-For isomer that produced a ketone... 2-bromobutane
-for isomer that produced primary, 2methylpropan-1-ol (think you were meant to draw two isomers)
-Carbocation was trigonal planar, 3 bond pairs equal repulsion, minimum repulsion, maximum separation
-KOH with alcohol, elimination, forms 2 methylprop-1-ene (something like that)

C
-Hydrogen expensive when it has to be contained at a high pressure, because expensive equipment, and expensive to create the pressure
- smelly ammonia allows leaks to easily be detected
2 additional pieces of info, availability of methane and hydrogen :s and percentage yield...
-Mixed with petrol, ammonia is a gas so mixing with petrol allows it to burn effectively :/
- Ammonia used as Hydrogen is made from the fossil fuels so would not be a good replacement. Biproduct of ammonia burning is not CO2

[Ash03]

in the text it said ammonia was difficult to ignite, so i said mixing with petrol aids in doing this

[itsmehello]

(Original post by Ash03)
in the text it said ammonia was difficult to ignite, so i said mixing with petrol aids in doing this

Yeah I had no idea what to write so I just put that it's a gas... and made up that with petrol it would burn more effectively

[Lil Monkey]

(Original post by itsmehello)
Yeah I had no idea what to write so I just put that it's a gas... and made up that with petrol it would burn more effectively

me too i put something similar!! i said that ammonia is very volatile and stuff so mixing it with petrol would make the fuel burn easily and cleanly!!!