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# *New* AS Chemsitry thread watch

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1. (Original post by hihihihi)
ok here's a quick question from OCR Chains and Rings june 2003 paper
first it asked you to write the equation for complete combustion of methanol but then it asks "Suggest why methanol is added to petrol"
only a 1 mark question but i'm guessing it has something to with the equation it asked you to write just before.
any ideas?
Is it something to do with methanol goes to complete combustion so a lot of energy is released from its combustion which is economic for use in petrol? hm
2. (Original post by FidoDiDo)
Well i would say .. due to multiple atomic overlapping the outmost electrons get delocalised..becuz they are charged particles they act as charge carriers .. soo carry an electric charge throughout the metallic lattice ..which enables the metal to conduct electricity..
one of the Mod 1 AQA mark schemes with that question said do not accept 'carry charge' or 'along the layers' or 'move through the metal' so terminology is really important. I put carry the electric charge too cos I can't really think of another way to say it Anyway they put the answer as:

(Delocalised) electrons
Move/flow in a given direction (idea of moving non-randomly)
or under the influence of applied pd

I like that atomic overlapping bit though, never knew that
3. a) write equation between reaction of calcium with water.

Ca + 2H2O ---> Ca(OH)2 + H2

b)When 1 g of calcium is placed in 200g of water, the temperature increases by 12.2 when the reaction is completed. The specific heat capacity of water c , is 4.2JGK
Calculate the heat releases in the experiment.

Working with Joules and kilograms (s.h.c. water = 4200 J kg^-1 K^-1)
∆Q = mc∆T = 0.2 * 4200 * 12.2 = 10248 kJ

c)Calculate the standard enthalpy change of the reaction is KJMol for your equation in [a].

Moles of calcium used (n) = mass/RAM = 1/40
∆H*r = -∆Q/n = -(10248)/(1/40) = -410 kJ mol^-1 (3s.f.)

d) use Hess' law and your results in [c] to calculate the standard enthalpy of formation of Calciumhydroxide.You also need the standard enthalpy of formation of water which is -286KJmol.

∆H*r = ∑(∆H*f of products) - ∑(∆H*f of products)
-409921 = ∆H*f of CaOH - -286
∆H*f of CaOH = -409921 -286 = -410 kJ mol^-1

e)calculate the volume of Hydrogen, measured at rtp, luberated in the expiremnt described in

moles H2 liberated = moles Ca used = 1/40
one mole of gas occupies 24 dm^3 at RTP, so 1/40 moles will occupy 24/40 dm^3

so 0.6 dm^3

edit - mistakes corrected, thx ram
4. mik1a is so hardworking
5. (Original post by z!D4N)
mik1a is so hardworking
Thanks..
I call it revision.
6. (Original post by mik1a)
a) write equation between reaction of calcium with water.

Ca + H2O ---> CaOH + 0.5H2

This is wrong, the right answer is:

Ca + 2H2O ---> Ca(OH)2 + H2
7. lemme help u guys... some of the most important equations to remember are: (as i remember only cuz i dont wanna look at my textbooks)

disproportionations:
CI2 + 2NaOH --> NaCIO + NaCI + H2O (cold)
CI2 + 2OH- --> CIO- + CI- + H2O (ionic)

3CI2 + 6NaOH --> NaCIO3 + 5NaCI + 3H2O (hot)
3CI2 + 6OH- --> CIO3 + 5CI- + 3H2O (ionic)

on its own:
3NaCIO --> NaCIO3 + 2NaCI (hot)
3CIO- --> CIO3- + 2CI- (ionic)

in acidic conditions:
CIO- + 2H+ + 2e- --> CI- + H2O
CIO3- + 6H+ + 6e- --> CI- + 3H2O

metal oxides + water:
Li2O + H2O --> 2LiOH
Na2O2 + 2H2O --> 2NaOH + H2O2
2KO2 + H2O --> K2O + H2O2 + O2

metal + water: (the important exceptions)
Mg + H2O --> MgO + H2 (hot steam)
Mg + 2H2O --> Mg(OH)2 + H2 (cold, slow)

metal nitrates decomposition:
2Ca(NO3)2 --> 2CaO + 4NO2 + O2
Na(NO3)2 --> NaNO2 + O2 (pale yellow nitrites)

other equations are so common sense... these are enough and the most important...
8. (Original post by mik1a)
Thanks..
I call it revision.
ur welcome... gimme some +ve rep then
9. (Original post by misty)
hey- what do u mean the calculation stuff? do you mean like titrations, enthalpy calculations etc..?
Yup that kind of stuff and moles and volumes and just easy stuff like that.
10. on a separate note:

Q: what did the goldsmith say to gold???
A: Au .... come back here!!

HAHAHAHHHAHAH

Au = Gold (btw... incase u didnt get it...)

And another one......

The name is Bond. Covalent Bond (said in a James Bond accent)

AHHAHHAHAHAHAHA

ciao .... revise hard
11. in the mass spetrometer why is it harder to knock out 2 electrons (to form +2 ions)? Is it because of the increased ionisation energy?
12. (Original post by Heidi)
in the mass spetrometer why is it harder to knock out 2 electrons (to form +2 ions)? Is it because of the increased ionisation energy?
yes that is correct. now gimme +ve rep. thx
13. (Original post by z!D4N)
yes that is correct. now gimme +ve rep. thx
Stop begging for + ve rep. no one will give u any

Stop acting like a begger
14. (Original post by daydream)
Stop begging for + ve rep. no one will give u any

Stop acting like a begger
how old r u? i wonder
15. (Original post by Heidi)
in the mass spetrometer why is it harder to knock out 2 electrons (to form +2 ions)? Is it because of the increased ionisation energy?
Yea precisely, when the gaseous atom or molecule is bombarded with electrons it takes energy (hence ionisation energies are always endothermic enthalpy changes) to remove the electrons. Successive ionisation energies always INCREASE.. so the 2nd IE > 1st IE, 3rd > 2nd, etc.. simply because electrons are being removed from increasingly positive ions. The attractive force between the outermost electron and nucleus is hence greater.
16. and how old are u?
17. Incidentally, i'm doing A2 this year.. but thinking back to unit 1 and the mass spectrometer.. where do the electrons come from, the ones which bombard the vapourised atoms / molecules entering the spectrometer.

I vaguely remember they're released from a titanium? tungsten? filament when electricity is passed through. Is that right, or am i going a little loopy? Chars all.
18. (Original post by Sahir)
Yea precisely, when the gaseous atom or molecule is bombarded with electrons it takes energy (hence ionisation energies are always endothermic enthalpy changes) to remove the electrons. Successive ionisation energies always INCREASE.. so the 2nd IE > 1st IE, 3rd > 2nd, etc.. simply because electrons are being removed from increasingly positive ions. The attractive force between the outermost electron and nucleus is hence greater.
Thanks, but could it also be that the chances for another electron being knocked off is very slim?
I just thought of that one
19. (Original post by Sahir)
Incidentally, i'm doing A2 this year.. but thinking back to unit 1 and the mass spectrometer.. where do the electrons come from, the ones which bombard the vapourised atoms / molecules entering the spectrometer.

I vaguely remember they're released from a titanium? tungsten? filament when electricity is passed through. Is that right, or am i going a little loopy? Chars all.
Yah filament it's heated and electrons are excited and can leave the filament which is accelerated towards teh sample to bombard them
20. (Original post by Heidi)
Thanks, but could it also be that the chances for another electron being knocked off is very slim?
I just thought of that one
Yea true, but that's a bit of a vague answer! Well not vague, just not err.. very chemistry-ish! Dunno if you'd get the mark(s) for that to be honest.

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