Chemistry Practice Exam 1 Discussion

[Blakhitman]

lol I will never believe that after having done NEAP 2010.

[kenhung123]

Hmm when some question says something like "what are the products" Do you assume only reacts once? Like in ethane+Cl2 do you assume no CH3CHCl2 forms since only 1 reaction..?

[stonecold]

Nahh, the reaction keeps on happening.  So you get chloro, then dichloro, then trichloro etc.

Well, that was the question on NEAP 2009 anyway...

[Greggler]

did lisachem 2010 today. MC raped me and i only got 14/20 =/ . but SA was really quite easy i thought. Still relatively pleased with a 68/76

I plan to do either neap or lisachem 09 tomoz.

[kenhung123]

OK serious question:
How do you determine the indicator suitable for a acid base titration?
I first thought you just look at reactants...the end point is approximately the solution added e.g. if you are adding weak base the pH would be around 7-9

But apparently you look at the products and determine the strength of acid base products e.g. HCl+NH3=>NH4+ + Cl- (weak acid and strong base) no idea how to predict that really...

[kenhung123]

Does COO- Hbond with water or ion-dipole?

Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?

[olly_s15]

Does COO- Hbond with water or ion-dipole?

Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?

the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens

[Mao]

Does COO- Hbond with water or ion-dipole?

Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?

the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens

incorrect. The CH2 group is not split by CH2 because they are the same environment. CH2 is only split by CH3, thus it is a quartet.

[kenhung123]

Ok so just consider half the molecule if there is a symmetrical one then>

[olly_s15]

Does COO- Hbond with water or ion-dipole?

Is the NMR spec for CH3-CH2-CH2-CH3 just a quartet and triplet?

the nmr spec is a triplet of a quartet (so a 12tet) for the middle ch2 hydrogens and a triplet for the terminal ch3 hydrogens

incorrect. The CH2 group is not split by CH2 because they are the same environment. CH2 is only split by CH3, thus it is a quartet.

*bows down to mao*

[stonecold]

Volumetric analysis question on Lisachem short answer 2008 = DOG ACT!

[crayolé]

300 ml of a 0.35 M 2 Ca(OH) solution was reacted with 300 ml of 0.40 M HCl .
The pH of the resultant solution is closest to:
A 0.82
B 1.12
C 12.88
D 13.18

I got a pH of 12.95 is that correct? So the closest would be C but the answer is D?

[stonecold]

It is Ca(OH)2

That is why your getting the wrong answer.

[minilunchbox]

300 ml of a 0.35 M 2 Ca(OH) solution was reacted with 300 ml of 0.40 M HCl .
The pH of the resultant solution is closest to:
A 0.82
B 1.12
C 12.88
D 13.18

I got a pH of 12.95 is that correct? So the closest would be C but the answer is D?

Can you even have Ca(OH)? Shouldn't it be Ca(OH)2 in which I got pH of 12.88 using it so the answer still isn't D. o-o

I don't even know what I'm doing anymore, argh.

[chansthename]

[OH-]=2*0.35
pOH= -log(0.7) = 0.155
Therefore pH=14-0.155= 13.86 (which is more than they give but IDK, i probably did something wrong)