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Chemistry: Post your doubts here!

Haya Ahmed

Haya Ahmed

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Can someone help me with any pdf(s) or tips or ideas about paper 3 chem AS because my exam is tomorrow so if you can help me please do :)
 
AbbbbY

AbbbbY

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Browny said:
For the practical paper can we get to test for gases other than NH3 and how to test for them?
Click to expand...

I think NO2 (?). It's a brown gas. The test tube turns brownish on the inside. It's given on the last page btw so just cross check from that.
O2 -> Relights a glowing splint
H2 -> Burning splint goes off with a pop
CO2 -> Turns limewater milky

What I usually advise people is to briefly smell the gas evolved. If it's ammonia, just write ammonia, don't waste your time checked for everything. If it's NOT ammonia, start with CO2 then go to O2 and lastly H2. I've never seen H2 show up. O2 twice. Ammonia A LOOOOT and CO2 quite often too.

For the Ammonia test if you end up performing it, make sure you use DAMP litimus paper or the colour wont change (Ligand exchange wont happen without water!).
Secondly, ensure that the litimus paper doesn't touch the test tube because you've already added an alkaline solution so don't want to get an incorrect result there.
 
AbbbbY

AbbbbY

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EddieX said:
i also got x=1
the are was the problem..easiest paper ive seen :/...or i overstudied :$:confused:
Click to expand...

Definitely the former. Recent P2's have been much more challenging. Anyway. The Organic will help you in P4. They might not have asked a lot of the reactions now but A2 organic is A2 inside the ring and AS outside it.
 
B

Browny

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AbbbbY said:
I think NO2 (?). It's a brown gas. The test tube turns brownish on the inside. It's given on the last page btw so just cross check from that.
O2 -> Relights a glowing splint
H2 -> Burning splint goes off with a pop
CO2 -> Turns limewater milky

What I usually advise people is to briefly smell the gas evolved. If it's ammonia, just write ammonia, don't waste your time checked for everything. If it's NOT ammonia, start with CO2 then go to O2 and lastly H2. I've never seen H2 show up. O2 twice. Ammonia A LOOOOT and CO2 quite often too.

For the Ammonia test if you end up performing it, make sure you use DAMP litimus paper or the colour wont change (Ligand exchange wont happen without water!).
Secondly, ensure that the litimus paper doesn't touch the test tube because you've already added an alkaline solution so don't want to get an incorrect result there.
Click to expand...
Can how can we test with limewater will they provide with the tube and all?
And what if the gas is poisonous then we cant smell it, who knows whether it is SO2.
 
AbbbbY

AbbbbY

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Browny said:
Can how can we test with limewater will they provide with the tube and all?
And what if the gas is poisonous then we cant smell it, who knows whether it is SO2.
Click to expand...

SO2 wont show up. NO2 is brown so you'll know when it shows up. Ammonia has a very distinct, pungent smell. Slightly smelling, not inhaling it all in should tell you whether it is Ammonia or not. I'm not saying you do this, just what I do and end up saving a lot of time and effort.

Never done a CO2 test in lab? :eek:

You basically take a test tube and put a lil bit of limewater in it (enough to submerge the delivery tube). Then you put the delivery tube inside and connect the stoppered end of the delivery tube righttt after mixing the reactants. If it turns milky, it's CO2, if it doesn't, it's something else. Make sure you have enough limewater inside. Limewater turns back clear on exposure to excess CO2!
 
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Browny

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AbbbbY said:
SO2 wont show up. NO2 is brown so you'll know when it shows up. Ammonia has a very distinct, pungent smell. Slightly smelling, not inhaling it all in should tell you whether it is Ammonia or not. I'm not saying you do this, just what I do and end up saving a lot of time and effort.

Never done a CO2 test in lab? :eek:

You basically take a test tube and put a lil bit of limewater in it (enough to submerge the delivery tube). Then you put the delivery tube inside and connect the stoppered end of the delivery tube righttt after mixing the reactants. If it turns milky, it's CO2, if it doesn't, it's something else. Make sure you have enough limewater inside. Limewater turns back clear on exposure to excess CO2!
Click to expand...
Why won't SO2 wont show up?
 
Namehere

Namehere

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AbbbbY said:
How do you test for SO2 gas? Why would it show up if you're never taught how to test for it -_-
Click to expand...

Don´t you use filter paper soaked with a bit of acidified potassium dichromate and when SO2 reaches it, it goes from orange to green? Not sure, maybe I´m wrong.
 
daredevil

daredevil

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Heyy guyss.... i am a little confused here....

so let's say that u have two hypotheticaal equations...

they have the reduction potentials of -0.15 and -1.15
which one of them will be reduced and which will be oxidised??
 
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