Qualification > Sciences
Need help on CIE Chemistry Paper 5!
moon:
F0r nov 2009 ppr52 I really need an explanation for Q1(f) & Q3(d) the markscheme is not giving an answer.I would really appreciate ur help.
ashish:
--- Quote from: moon on October 17, 2010, 01:08:08 am ---F0r nov 2009 ppr52 I really need an explanation for Q1(f) & Q3(d) the markscheme is not giving an answer.I would really appreciate ur help.
--- End quote ---
q1(f)
H = Mc deltaT
you have to take M as the total volume of the solution
H= VT*4.3 * delta T
NaOH is the reagent in excess and HCl is the limiting reagent
therefore you should use the limiting reagent for calculation the heat change for 1 mole
suppose you use 20cm3 of acid of concentration 2.0 mol/dm3
1000cm3 of HCl contains 2.0 mol HCl
20cm3----------- (2.0/1000)*20
=0.04
then 0.04 mole of HCl gives H J of heat (VT*4.3 * delta T)
1 mole----------- (H/0.04)*1 J
Q3(d)
you have to work out the molecular formula let say your mean value for Cu was 2.00
element mass Ar mole /simplest
O 1.00 16.0 0.0625 1.98 =2
Cu 2.00 63.5 0.0315 1
Copper (I) oxide
CuO2
Deadly_king:
--- Quote from: moon on October 16, 2010, 11:22:25 pm ---For diprotic acids number of moles should still not exceed 0.06/2 since 1 mole of acod already provides 2 moles of H+.
Why do we have to divide by 2 and not multiplying??????????? 1mole NaOH reacts with 1mole of sulphuric acid and hence reacts with 2H+
so 0.06moles NaOH reacts with 0.06*2 of H+ Isn't it???????????????? I still didn't understand this point and how can we keep the total final volumes the same in each experiment?????????????????? I really need help urgently cuz the markschemes and the examiner's reports are not very useful............PLZ HELP!!!! thanx in advance :)
--- End quote ---
Nan.........1 mole of sulfuric acid provides 2 moles of H+
2NaOH + H2SO4 ----> Na2SO4 + 2H2O
1 mole of sulfuric acid reacts with 2 moles of NaOH
In your case 0.03 moles of sulfuric acid is required to neutralise 0.006 moles of NaOH because sulfuric acid provides 2H+
Total volume is kept constant so that volume can be used as a measure of the concentration of the solutions. You keep total volume constant by adding water.
If you have any problem, let us know and we'll try to help you as much as you can. :)
Relax dude ;)
moon:
Q3(d)
you have to work out the molecular formula let say your mean value for Cu was 2.00
element mass Ar mole /simplest
O 1.00 16.0 0.0625 1.98 =2
Cu 2.00 63.5 0.0315 1
Copper (I) oxide
CuO2
How did u get an average 2??? my average is 3.983 so the formula of copper oxide is CuO PLZ help..... thanks 4 ur help
moon:
--- Quote from: Deadly_king on October 17, 2010, 08:06:59 am ---
Total volume is kept constant so that volume can be used as a measure of the concentration of the solutions. You keep total volume constant by adding water.
If you have any problem, let us know and we'll try to help you as much as you can. :)
Relax dude ;)
--- End quote ---
what is the volume of water do we have to use???????
Thanx a lot for ur help..
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