Chem qu (1 Viewer)

[richz]

no, i dont think so, its converting moles to litres.

 

[MuffinMan]

umm pass me the q! i wanna do it!

 

[Dreamerish*~]

yeah i guess so........

Yeah I suppose the question is somewhat badly phrased.

But with those multiple choice questions, you can't read too deeply into them. In this case, just pick the one that copper forms a precipitate with, because that's what they asked, and that's the most likely answer. If you think too much, you might end up confused and picking the wrong answer.

A couple of guys from my grade did that. They overanalysed the very first multiple choice question and thought it was a trick. It wasn't.

 

[MuffinMan]

what is the question? lol cant answer it if i dont have it

 

[richz]

lol maybe i do

which one u talking about hsc??

 

[MuffinMan]

the one ur doing rite now
umm how many q's are there
i was looking at the first multiple choice lol
its dead easy

 

[richz]

o there are lots of multis, search thru this thread

 

[velox]

oh yeh crap, shouldnt have rushed through the multi choice in 6.5 mins.

I guessed this one, do i just have to remember those flowcharts?

thats the question. I agree its a bit vague aswell.

 

[richz]

hmm... anything else be4 i go?? becuz my laptop is running low on batteries and i need to study for my chem, got the damn exam tomorrow and i dont even freaken understand industrial chem, its so stupid id prefer shipwrecks arghh... theres like 25 marks down the drain

 

[velox]

good luck =) Industrial chem is easy, you'll be fine.

 

[richz]

lol, its all abt regurgitating the freakn book argh.... anyway good luck to u too

 

[velox]

what about this one?
We never did this stuff properly =/

 

[ishq]

We were taught:

The ester methy propanoate is prepared by refluxing a mixture of methanol and propanoic acid with conc sulfuric acid. After the reaction mixture has been cooled and poured into a large volume of water, the following procedure is used to purify the substance -

1. Stir the misture and separate into two layers. Discard the aqueous layer.
2. Add a small amount of sodium carbonate to the organic layer. Add water and shake the mixture. Allow the mixture to separate into two layers. Discard the aqueous layer.
3. Allow the organic layer to stand over a drying agent (anhydrous calcium chloride). Filter off the drying agent.
4. Distill the organic layer to obtain the PURE ester.


So, shouldnt it be Beaker 4?
Why does it say Beaker 2?

 

[Jumbo Cactuar]

No, bisulfate ion is a weak acid with pKa of 1.92 I think. Hence you can't assume it deprotonates fully, as it can't unless in the presence of base.

Hence the assumption.

I would hate a multiple choice q. without the assumption::

[H+] = 0.0005 + y
[HSO4-] = 0.0005 - y
[SO4 2-] = y

0.0005^2 - y^2 = y * 10^-1.99
0 = y^2 + y * 10^-1.99 - 0.00000025
2y = -10^-1.99 + &sqrt;(10^-3.98 + 0.000001)
y = 2.437 * 10 ^-5

[H+] = 0.00052437
pH = -log 0.00052437
= 3.280

Which makes the question kind of silly ... !

 

[velox]

i have no idea.......

 

[Jumbo Cactuar]

We were taught:

The ester methy propanoate is prepared by refluxing a mixture of methanol and propanoic acid with conc sulfuric acid. After the reaction mixture has been cooled and poured into a large volume of water, the following procedure is used to purify the substance -

1. Stir the misture and separate into two layers. Discard the aqueous layer.
2. Add a small amount of sodium carbonate to the organic layer. Add water and shake the mixture. Allow the mixture to separate into two layers. Discard the aqueous layer.
3. Allow the organic layer to stand over a drying agent (anhydrous calcium chloride). Filter off the drying agent.
4. Distill the organic layer to obtain the PURE ester.


So, shouldnt it be Beaker 4?
Why does it say Beaker 2?

It says the beakers are labelled in order of collection AND that pure substances were collected. Since Methyl Propanoate has the second lowest BP it would have been collected in beaker 2.

 

[ishq]

It says the beakers are labelled in order of collection AND that pure substances were collected. Since Methyl Propanoate has the second lowest BP it would have been collected in beaker 2.

Ohh!!!!!

You mean like Fractional Distillation?
I get it...
So the four substances are the the reactants, ester and water...

Understood...

 

[Pace_T]

so beaker four would be propanoic acid right?

 

[velox]

How do i find out which one is the cathode? *what a dumb queestion *

 

[richz]

huh.......... u know which one is the most reactive. zn is the most reactive so oxidation happens there therefore that is the anode therefore cathode is cu so answer is
D