OCR chem AS Watch

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idiopathic
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#21
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#21
(Original post by kay123)

and ermm theres this one calculaion question:MgO + 2HNO3 = Mg(NO3)2 + H2O

calculate the volume of 0.4mol dm-3 HNOs is required to react with 2g of the MgO
ne ideas...?
y am i the only one wid loads of questions!?!
MgO + 2HNO3 = Mg(NO3)2 + H2O

Moles (of MgO) = mass/mr
moles = 2/(24.3+16)
moles = 0.0496 moles

ratio of MgO : HNO3 = 1:2
.'. moles (of HNO3) = 2* 0.0496
moles = 0.993

using moles = volume/24dm³
vol (HNO3) = moles * 24
vol (HNO3) = 0.993*24
vol (HNO3) = 2.38 dm³


(Original post by kay123)
in last years june paper at the end there was this question asking to describe intermolecular bonding in CH4, wat is the tyep of bonding?
Van der Waal's forces (instantaneous dipole-induced dipole)
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violet
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#22
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#22
I thought they were called instantaneous dipole-induced dipoles...
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idiopathic
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#23
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#23
(Original post by violet)
I thought they were called instantaneous dipole-induced dipoles...
Yeah I changed them.
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violet
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#24
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#24
(Original post by endeavour)
Yeah I changed them.
Oh right! You could have changed it to something shorter though.. it would have made my life a lot easier :rolleyes:
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Aired
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#25
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#25
Just taken the exam! Chains & Rings and How Far How Fast were suspiciously easy, not a single calculation on Chains & Rings...
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Talya
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#26
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#26
Chains and rings was horrid. That stupid essay!

Great essay on HfHf, 7 easy marks there

Foundation was alright. I've forgotten about it already though.

How did everyone else do?

-Kavanne
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Aired
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#27
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#27
I found Chains and Rings easier. The only thing I didn't really know was 2 alternate uses for CFS's. I wrote about using them as a propellant in aerosols, but I couldn't think of anything else.

Which parts did you find difficult Kavanne?
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Talya
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#28
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#28
On the question on foundation about the compound X of Ti and Cl, what was the empirical formula? I got tiCl4, but some people in my school got TiCl5.

Which is right? What did you get?

-Kavanne
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Aired
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#29
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#29
I didn't do foundation, I did it in January. Sorry!
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shyopstv
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#30
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(Original post by Aired)
I found Chains and Rings easier. The only thing I didn't really know was 2 alternate uses for CFS's. I wrote about using them as a propellant in aerosols, but I couldn't think of anything else.
Fire extinguishers. They also asked for reasons but I couldn't think of any so I just went on about how stable they are therefore won't react with gases in the fire even though it is hot

I also got the question about the structure of the ester wrong but apart from that I found it very easy. HFHF was harder though - what did everyone put for the question asking why ammonia isn't used for rocket fuel. And was the enthalpy change in that question around -570?
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Pete.S
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#31
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#31
TiCl4 is correct thats what i got, i done foundation and hfhf, went quite well. There wasnt many calculations in foundation this time around. What did you get for the last question in foundation? the one with why nitrogen was higher than oxygen or sumthin like that
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Pete.S
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#32
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#32
-570 sounds familiar, the ammonia one said to look in that table so i said the triple nitrogen bond was highly stable and unreactive
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Aired
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#33
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I got -577 for the enthalpy change I think. For the ammonia question I think I said that it would have a much lower activation energy and so may ignite too easily.
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Star_ice
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#34
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yeh i got -577 to. in chains and rings wat did u all do for the ch2c=ch2 (or sumthing lyk that) wen added 2 HBr and u had 2 hav 3 isomers. but for sum reason i didn't see how there were 6 hydrogens!! :confused:
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KAISER_MOLE
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#35
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#35
I got 577 somewhere too.


Mistakes I know I made =>
Chains and Rings, about CFC's, put down fire extinguisher but couldn't think of propellant o__0 ..I explained about free radicals combining with other fire=propagating free radicals though.

HFHF - what produces Nitrus dioxide or whatever, should have been catalytic converter in car engine, I put fertiliser as I did not know :P

Also, the question just after that on ionic equations I will probably have gotten wrong.

Other than that it was exceptionally groovy ...I hope ;/
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shyopstv
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#36
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#36
(Original post by KAISER_MOLE)
HFHF - what produces Nitrus dioxide or whatever, should have been catalytic converter in car engine, I put fertiliser as I did not know :P
:eek: Just realised how obvious it was. I put Nitrificication when ammonia is converted to NO2 by Nitrosomonas bacteria :rolleyes:

For the bromine isomer question, you get a halogenoalkane when you add HBr to an alkane in this case is was dibromopropane - I drew 1,1 1,2 and 1,3
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KAISER_MOLE
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#37
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#37
I drew 1,1, 1,2 and 1,3 too, I was a bit ambivalent on whether it ought be 1,3 or 2,2 ....but I didn't like the look of 2,2 :P:
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Talya
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#38
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(Original post by KAISER_MOLE)
I drew 1,1, 1,2 and 1,3 too, I was a bit ambivalent on whether it ought be 1,3 or 2,2 ....but I didn't like the look of 2,2 :P:
It can't have been 1,3 because you can't have a double bond between the carbon's number 1 and 3. The bromines could only add onto the carbons that had been involved in the double bond before....

-Kavanne
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Fluent in Lies
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#39
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Found all three modules really good, hfhf was a bit dodgy, but the essya question at the end was nice.

What the hell was the bit about some bloke swallowinf the CFC and blowing out a candle. I mean, who cant blow out a candle?

WHat did people put as properties, I guessed on-flammable and non-toxic. But I dont know, maybe he exploded and was poisoned, stupid question imo.
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Fluent in Lies
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#40
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(Original post by KAISER_MOLE)
I drew 1,1, 1,2 and 1,3 too, I was a bit ambivalent on whether it ought be 1,3 or 2,2 ....but I didn't like the look of 2,2 :P:
1,1 1,2, 2,2
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