Chemistry: Post your doubts here!

[Firebender]

Guys, I'm really panicking right now: http://www.xtremepapers.com/papers/...and AS Level/Chemistry (9701)/9701_y12_sy.pdf

I was looking through the AS level chemistry syllabus and I came across the learning outcomes of the chapter Electrochemistry(Page 19 and 20 in the link). I don't know any of that stuff. AT ALL. I don't remember this being discussed in class or appearing in any exams. And I scored well on my chemistry mock. What's going on?

 

[histephenson007]

please tell me how is the answer D?

2,4- DNP ( or phenylhydrazine in this case) is used as a test for Carbonyl groups. The test happens because the hydrogens on the hydrazine group (from the NH2) undergo a condensation reaction with the Carbonyl group (-C=O )to form a water molecule. In compound P, the carbonyl group is the one on the second Carbon from the left ( note that DNP doesn't react with esters which is given in the middle of the molecule to confuse you).

So now, just connect the Carbonyl group to the hydrazine group, you should be able to see that D is the only option available.

 

[histephenson007]

Guys, I'm really panicking right now: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_y12_sy.pdf

I was looking through the AS level chemistry syllabus and I came across the learning outcomes of the chapter Electrochemistry(Page 19 and 20 in the link). I don't know any of that stuff. AT ALL. I don't remember this being discussed in class or appearing in any exams. And I scored well on my chemistry mock. What's going on?

FYI, all the text in bold are for A2 level.

 

[CaptainDanger]

Guys, I'm really panicking right now: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_y12_sy.pdf

I was looking through the AS level chemistry syllabus and I came across the learning outcomes of the chapter Electrochemistry(Page 19 and 20 in the link). I don't know any of that stuff. AT ALL. I don't remember this being discussed in class or appearing in any exams. And I scored well on my chemistry mock. What's going on?

Talking about the stuff written in BOLD?

 

[geek101]

can anyone please post a link for the paper 1s' of 2001 and 2002 both june and november! thanx! needed in emergency!!

 

[Scafalon40]

A. In the reverse reaction of the first reaction, HSO3- acts as a OH- donor. Hence it might be called a base.
B. The reaction is SO2 - > SO3- , Sulphur actually got oxidised from +4 to +6. So, its a reducing agent, not an oxidising agent.
C. SO3 (2-) accepts a proton in the reverse reaction of second reaction. So, it acts as a base. Not an acid.
D. The second reaction isn't a redox reaction at all. So, SO3 (2-) can't be any agent.

Since when is a base an acceptor of OH^- ions?

 

[histephenson007]

Since when is a base an acceptor of OH^- ions?

I said OH- donor. Hence, a H+ acceptor.

 

[iKhaled]

i have some questions in chemistry P1 May/June 2007

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

Q9
Q18
Q27
Q40

 

[Scafalon40]

I said OH- donor. Hence, a H+ acceptor.

Never heard of that kind of logic..

 

[histephenson007]

Never heard of that kind of logic..

lol... I was just trying to make sense of the question I dunno the answer to. Maybe my head's starting to rust. Signing off now . Adios

 

[Scafalon40]

lol... I was just trying to make sense of the question I dunno the answer to. Maybe my head's starting to rust. Signing off now . Adios

Bye, and a penny for you thoughts... is that ion even a Lewis base?

 

[geek101]

i have some questions in chemistry P1 May/June 2007

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_1.pdf

Q9
Q18
Q27
Q40

Q9) theres kind of a shorcut explanaion to this, since the products of reaction two are 1/2 moles, so its going to be anything with a power of 1/2 which is actually square root, the only option with an underroot 2 is A.

Q18) the solid nitrate is NH4NO3 > N2H4O3

Q27) propanal and propan-2-ol both have the tendency to be oxidized. propanal to propanoic acid and propan-2-ol to propanone. When they get oxidized both change the colour of KMnO4 from orange to green.

Q40) inorder to break an ester bond there must be either a dilute acid or alkali. the only of these is 1 (acid), thus being the only answer. heres a little info on ester hydrolysis...
http://www.chemguide.co.uk/organicprops/esters/hydrolysis.html

 

[hmlahori]

histephenson007 already answered 3 and 26 so ill chip in to the 16. If something is being precipitated then it must be insoluble, of all the options CaCO3 is the only insoluble salt, or at least thats what i think.

Yes thats what i thought it would be but i still wasnt sure. well thanks!

 

[XPFMember]

Assalamoalaikum wr wb!

need help in these mcqs, please:

 

[CaptainDanger]

Assalamoalaikum wr wb!

need help in these mcqs, please:

View attachment 7843View attachment 7844View attachment 7845View attachment 7846View attachment 7847View attachment 7848

Walikum Salaam!

28 - A is a test for aldehyde.
C is test for both aldehyde and ketone.
D is used for the reduction of carbonyl compounds.

B is the correct answer as it is test for alkenic double bond. Cyclohexene having double bond will discharge the colour of Br2 while cyclohexanol won't...



35- Not sure.


36-

X can be Carbon, Nitrogen and Sulpher.

Y can be CO, NO, SO2.

Z can be CO2, NO2. (No SO3, Oxidation of SO2 requires catalyst so its not on the spot reaction.)

1- It does increase for NO and CO.
2- CO and SO2 does have lone pairs.
3- CO2 and NO2 have two oxygen atoms.

So only 1 is correct.



10- Acid is a proton donor, Base is aproton acceptor. In the second reaction HSO3- accepts the proton making it a base. Further explained here : Chemistry: Post your doubts here!



35.

1 - Ammonium Salt with strong base gives ammonia.

2- Neutralization Reaction. So that is correct too.

3- Limewater absorbs CO2 making limestone.

A is the answer.



36 - X can be Carbon, Nitrogen and Sulpher.

Y can be CO, NO, SO2.

Z can be CO2, NO2. (Oxidation of SO2 requires catalyst Vanadium Oxide so it is not on the spot reaction)

1- X forms a basic hydride is correct as NH3 is basic.

2- Y is a diatomic molecule is correct as you can see CO and NO are diatomic.

3- Z is a polar molecule. NO2 is polar.

So all are correct making the answer A.

 

[gary221]

Cud sum1 tell me hw v calculate the no. of moles required?? Ans is C, btw

 

[étudiante]

Cud sum1 tell me hw v calculate the no. of moles required?? Ans is C, btw
View attachment 7849

first try understanding in terms of ethene...
ethene has 1 double bond ryt? if u saturate it, u get ethane... draw out these 2 n see how many H is extra (u will see its 2)
now apply dis 2 da question... how many bonds do we need 2 saturate? 5 in total ryt? count it out, 1 bond in 1 chain n 2 bonds in the oder 2... dat makes 5 moles...
(as 1 mole of H2 has 2 moles of H atoms in it...)

 

[gary221]

first try understanding in terms of ethene...
ethene has 1 double bond ryt? if u saturate it, u get ethane... draw out these 2 n see how many H is extra (u will see its 2)
now apply dis 2 da question... how many bonds do we need 2 saturate? 5 in total ryt? count it out, 1 bond in 1 chain n 2 bonds in the oder 2... dat makes 5 moles...
(as 1 mole of H2 has 2 moles of H atoms in it...)

oh bt hw did u know 5 bonds hv been saturated??
thnx, nywy...
P.S. I m kinda bad at organic chem...

 

[étudiante]

oh bt hw did u know 5 bonds hv been saturated??
thnx, nywy...
P.S. I m kinda bad at organic chem...

see the question... in the residue molecule, dere is 1 double bond left in da molecule n 2 in da oder 1.. n dere r 2 moles of the second molecule..
so dats 1 + 2(2) = 5
ur welcum...
dats wat u think.... its jst practice

 

[XPFMember]

Walikum Salaam!

28 - A is a test for aldehyde.
C......

JazakAllah khairen