Chemistry: Post your doubts here!

[megamind]

Oops, It's C, was my second choice. LOL
No idea why though..

diprotic acis have two end points with monobasic bases
so dibasic Mgo will noly have one one end point with diprotic acid

if you need futher help check out xtremepaper's chemistry revision

 

[Alice123]

https://www.xtremepapers.com/community/attachments/chm4-pdf.2784/
Is this useful for A2 chem???

 

[snowbrood]

littlecloud11
To Identify oxide of nitrogen 0.1 mol of oxide is mixed with an excess of hydrogen and passed over a catalyst at suitable temperature
NxOy + H2 on heating with catalyst gives xNH3 +yH2O
the produced weighs 7.2g the ammonia produced is neutralized by 200cm^3 of 1.0 moldm^-3 Hcl
what is the formula of the oxide of nitrogen
tell me why the answer is N2O4

Aslam Alaikum
sure buddy.
water produced weighs 7.2g mr of water 18
number of moles of water 7.2/18=0.4
ammonia is neutralized by 200cm^3 of 1moldm^-3 HCl u might know NH3+HCl-NH4Cl
so number of moles of hcl and ammonia should be same inorder to react so number of moles of ammonia are
(200/1000)*1=0.2.
number of moles of ammonia represent x=0.2
number of moles of water represent y=0.4
multiply those both by 10 u get 2 and 4... hope i was able to help

 

[A*(a*)]

diprotic acis have two end points with monobasic bases
so dibasic Mgo will noly have one one end point with diprotic acid

if you need futher help check out xtremepaper's chemistry revision

but the answer is D! sir.

 

[A*(a*)]

diprotic acis have two end points with monobasic bases
so dibasic Mgo will noly have one one end point with diprotic acid

if you need futher help check out xtremepaper's chemistry revision

https://www.xtremepapers.com/community/threads/hardest-chemistry-mcqs-ever.25075/

 

[zain786]

I have trouble in doing paper 5 chemistry (Planning, analysis & evaluation). Can anyone please tell me if there is any format in answering the questions in paper 5?
If possible can anyone please show me a full answer for at least a paper?

 

[asd]

Can we describe Dehydration of alcohols and hydration of ethene as electrophilic reactions?

 

[KurayamiKimmi]

https://www.xtremepapers.com/community/attachments/chm4-pdf.2784/
Is this useful for A2 chem???

It looks pretty useful , save for the extra details here and there.

 

[syed1995]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

Question No 3 Part c .. where is it mentioned that which reaction is Reaction 1.. From where does one know which reaction to point over here ?

I know that displacement reaction will occur over here. But how do we know whether we have to give a sulfate/nitrate/chloride or w/e salt?

 

[PANDA-]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_22.pdf

Question No 3 Part c .. where is it mentioned that which reaction is Reaction 1.. From where does one know which reaction to point over here ?

I know that displacement reaction will occur over here. But how do we know whether we have to give a sulfate/nitrate/chloride or w/e salt?

Well, they did say instead of an acid, the only acid in the reactions above is H2SO4... That's the reaction Ba(OH)2 -> BaSO4

 

[syed1995]

Well, they did say instead of an acid, the only acid in the reactions above is H2SO4... That's the reaction Ba(OH)2 -> BaSO4

HCl and HNO3 are not acids? the data given below is for part d. Look at the table .. there's HNO3 used .. HCl as well how would be know what to use?

 

[aalmuhannadi]

Can we describe Dehydration of alcohols and hydration of ethene as electrophilic reactions?

Dehydration reactions aren't electrophilic, they're elimination reactions, and, like with hydration, have their own mechanisms separate from electrophilic reactions

 

[aalmuhannadi]

HCl and HNO3 are not acids? the data given below is for part d. Look at the table .. there's HNO3 used .. HCl as well how would be know what to use?

Reaction 1 is labelled as going from compound W to compound U. Another way of going to compound U is from T (Barium hydroxide) by adding sulfuric acid, and they are asking what can you use instead of the sulfuric acid? Well from this path you'd know that compound U is barium sulfate because adding H2SO4 to barium hydroxide would give you barium sulcate; now why would you use anything other than a sulfate compound to make barium sulfate? if you added sodium chloride for example, you would get a chloride and not a sulfate, so doesn't it sound reasonable to use a sulfate but NOT an acid which the question says? So if you can't use H2SO4, then another thing you could use is Na2SO4 because that would still react with barium hydroxide to give barium sulfate.

 

[syed1995]

Reaction 1 is labelled as going from compound W to compound U. Another way of going to compound U is from T (Barium hydroxide) by adding sulfuric acid, and they are asking what can you use instead of the sulfuric acid? Well from this path you'd know that compound U is barium sulfate because adding H2SO4 to barium hydroxide would give you barium sulcate; now why would you use anything other than a sulfate compound to make barium sulfate? if you added sodium chloride for example, you would get a chloride and not a sulfate, so doesn't it sound reasonable to use a sulfate but NOT an acid which the question says? So if you can't use H2SO4, then another thing you could use is Na2SO4 because that would still react with barium hydroxide to give barium sulfate.

See.. Now I feel like a fool.. I always oversee things like these. I didn't find the word "reaction 1" on the whole table even though I looked at it 5 times.. This is where I lose most of marks.. Now I just saw it.. marked from W to U.. lol Thanks man.

 

[aalmuhannadi]

See.. Now I feel like a fool.. I always oversee things like these. I didn't find the word "reaction 1" on the whole table even though I looked at it 5 times.. This is where I lose most of marks.. Now I just saw it.. marked from W to U.. lol Thanks man.

Hahahaha it's cool believe it or not I missed it the first time I did this paper too until my teacher pointed it out!

 

[syed1995]

Hahahaha it's cool believe it or not I missed it the first time I did this paper too until my teacher pointed it out!

Lol the funny thing is I did MJ var 1 and it had the same question and I missed it thought the first equation which we made was the first reaction.. Ironically In that question that was the case and my answer came correctly haha..

 

[Ashique]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_43.pdf
Q4 b i)
can anyone tell me how to find D ?

If you first of all count the number of carbons in the given diagram, you'll find that it has 8 carbons. D has 9. You'll also notice that I2 + OH- was added followed by H+ ions. So the immediate though that should hit you is the tri iodomethane test. You must know that it is a test for the presence of -COCH3 in a compound. The only place this could have been on the ring is the CO2H. So replace the H in the OH by COCH3 in the ring.

 

[megamind]

but the answer is D! sir.

F*** why

 

[megamind]

https://www.xtremepapers.com/community/attachments/chm4-pdf.2784/
Is this useful for A2 chem???

thanks very useful

 

[daredevil]

CH3CH2COCl + H2NCH2CH2CH3 = CH3CH2CONHCH2CH2CH3 + HCL , why is the reaction mechanism nucleophilic substitution in this case. Please explain

umm i guess the Cl- from the 1st mess of a molecule ( ) gets SUBSTITUTED by the whole mess of an anion ( ) from the 2nd molecule and HCl is formed as a result