Chemistry: Post your doubts here!

[hassam]

it shud not be molecular ion i guess....thats inappropriate word

 

[DragonCub]

Does it have to do anything with d+ and d- ...

No, it's totally irrelevant. What determines the chiral centre are four groups with different atoms or structures, not with different relative charges.

and when calculating enthaply change for example in reaction : Ca(s) + 2H2O(l) = Ca(OH)2 (aq) + H2 (g) and u r given Q, which moles do u take from Ca or H2O ?? Thanks so much

Mole of Ca or mole of H2.
In fact, the equation must first be stoichiometrically balanced (balanced to smallest possible integers), and then calculate the resultant enthalpy change. For example, A and B react to from C and D. Even if the balanced equation is 9A + 11B = 12C + 10D, it is still balanced to smallest integers. Enthalpy change (per mole) is still the total change according to this equation.
So the enthalpy change is more like the change "per balanced equation".

 

[DragonCub]

it shud not be molecular ion i guess....thats inappropriate word

I remember that in IGCSE Chemistry textbook the ions consisting of groups of atoms are called molecular ions, like SO4(2-), CO3(2-), NO3(-) and NH4(+). The complex ion is quite similar. Or should we call it "multi-molecular ion"? (Just kidding)

 

[hassam]

why we acidifiy solution containig fe 2+ ....when trying to dtermine its conc.

 

[girlscampisra]

please make a separate thread for A2 chem :s this is so confusing!

 

[RGBM211]

Yes please make a seperate A2 thread for chem

 

[saudha]

Yes please make a seperate A2 thread for chem

ur doing 34 and 42?

 

[smzimran]

girlscampisra
RGBM211
histephenson007
hassam
saudha
and every one else:
Here lets use this thread for A2 only chemistry doubts:

http://www.xtremepapers.com/community/threads/chemistry-p4-a2-only.15983/

 

[RGBM211]

ur doing 34 and 42?

i am done with paper 31 now i have paper 4 left

 

[farhanaldinho11]

hey can anyone tell abt chem p34 guess...??.PLXXXX...

 

[JJHOLIC]

did anyone take chemistry p 52? how was it?

 

[usmiunique]

ASA,
Can anyone explain the chromatography thing? like what is the stationary phase? what is the mobile phase? what are the two types of seperation techniques used in chromatography, like adsobtion and partition?
I have read it many times in the support booklet and in Chemguide but still can't understand it.. any help would be greatly appreciated!

 

[usmiunique]

why we acidifiy solution containig fe 2+ ....when trying to dtermine its conc.

we determine the conc. of fe2+ by titrating with MNO4- ions and the half eqn of MNo4- ions is
MnO4- +8H+ +5e- -------->Mn2+ +4H2O
this eqn has H+ ions.. which are supplied by the acid when it ionises it solutions!

 

[Pratik.Dhakal]

did anyone take chemistry p 52? how was it?

it didn't went too much well and how about yours ??

 

[angelicsuccubus]

did anyone take chemistry p 52? how was it?

umm weird? the first question was.. i didn't know what to write for any of it. And the second was okay

 

[JJHOLIC]

it didn't went too much well and how about yours ??

mine too.... didnt do well... especially the first question.... i "tried" to answer the question but not confident...

 

[angelicsuccubus]

mine too.... didnt do well... especially the first question.... i "tried" to answer the question but not confident...

it was a strange one.. pretty sure they'll get a bunch of weird anwers for that questions

 

[JJHOLIC]

umm weird? the first question was.. i didn't know what to write for any of it. And the second was okay

yea i agree found it weird.... for the second question did you draw a curve or line of best fit? for the relationship between 1/v and p?

 

[hihi]

No, it's totally irrelevant. What determines the chiral centre are four groups with different atoms or structures, not with different relative charges.

Mole of Ca or mole of H2.
In fact, the equation must first be stoichiometrically balanced (balanced to smallest possible integers), and then calculate the resultant enthalpy change. For example, A and B react to from C and D. Even if the balanced equation is 9A + 11B = 12C + 10D, it is still balanced to smallest integers. Enthalpy change (per mole) is still the total change according to this equation.
So the enthalpy change is more like the change "per balanced equation".

Thank you so much !!

 

[lavanyamane]

How was chem p 22? It was easy and there was 4 questions instead of 5!

Mine was great! It was really short and quite simple