Chemistry: Post your doubts here!

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s08_qp_2.pdf
Question 4bii

 

[periyasamy]

Can someone explain Q6f(ii) & (iii)? (My doubt is actually iii, so work on that one first, I just want to make sure if my reasoning behind ii is correct)

Thank you!

Yo,.I think i can explain u this.Its a shape that u have to imagine.
K to do this u have to imagine the struc.Its a bit hard to explain i will try my best.
The drawing i drew is how the bond lines look when they r rotated around.Thats why j is selcted.SEE the right hand pattern .....
The idea for the last part is u need to find smthg that is totally diff than all others but as u know rotation must be on the same plane.
For f n g the right part had showed all possibilities with such arrangement so u must take h as an example for right hand side.Now to sort the left side,u need tomake sure its diff than h.So u will get a new isomer.Hope u understand......

 

[BeBeskii108]

Describe and explain how the solubility of magnesium sulfate compares to that of barium sulfate? Anyone please ! [4 points]

 

[daredevil]

why carboxylic acid does not undergoes nuclophilic addition by HCN

ummm is it a past papr question??

bcz i think it just doesnt happen... like the reaction just doesnt occur with carboxylic acids

 

[daredevil]

Describe and explain how the solubility of magnesium sulfate compares to that of barium sulfate? Anyone please ! [4 points]

Hey I have this question and answer. You can adjust your answer accordingly:

Q. Describe and explain the trend in the solubility of the sulfates of the group II elements.

Ans.
- Solubility decreases (down group II) [1]
- lattice energy decreases [1]
- solvation/hydration energy (of cation) decreases [1]
- but more so than lattice energy / is not able to overcome LE [1]
- (delta)Hsoln becomes more endothermic / positive / less exothermic [1]

[max 4]

 

[Namehere]

Yo,.I think i can explain u this.Its a shape that u have to imagine.
K to do this u have to imagine the struc.Its a bit hard to explain i will try my best.
The drawing i drew is how the bond lines look when they r rotated around.Thats why j is selcted.SEE the right hand pattern .....
The idea for the last part is u need to find smthg that is totally diff than all others but as u know rotation must be on the same plane.
For f n g the right part had showed all possibilities with such arrangement so u must take h as an example for right hand side.Now to sort the left side,u need tomake sure its diff than h.So u will get a new isomer.Hope u understand......

Nah don´t get it I seem to get part iii, but now I dont understand what u mean with part ii.

 

[sameen saeed]

can anyone tell me that in AS practical what does permanent colour change refer to ?
does it refer to first appearance of colour change or we have to continue to add titre to see any change.

 

[Namehere]

can anyone tell me that in AS practical what does permanent colour change refer to ?
does it refer to first appearance of colour change or we have to continue to add titre to see any change.

Permanent colour, just like the name suggests. So it would be the colour of the solution for which it does not change anymore.

 

[A star]

can anyone tell me that in AS practical what does permanent colour change refer to ?
does it refer to first appearance of colour change or we have to continue to add titre to see any change.

there is a seperate threads that creep up for the practical see them and one piece of advice I can give what ever you do keep calm cause in 1 hour 30 min there is no recovery time

 

[sameen saeed]

Permanent colour, just like the name suggests. So it would be the colour of the solution for which it does not change anymore.

sometimes it happens that the changed colour which seems to permanent disappears after some time then what to do?????consider that permanent or keep adding titre

 

[periyasamy]

Nah don´t get it I seem to get part iii, but now I dont understand what u mean with part ii.

K.Let me think agn.Sorry.

 

[goodluckayesha]

how much marks do we need to score to get an A in Chem P1 and P2?

abt 30 in ppr 1 and abt 48-50 in ppr 2 this way ull get an A easily and in A2 it will be easier to get an A*

 

[goodluckayesha]

How did you come to that conclusion , what i know about pka that its given by -log ka .. why pka is ph of buffer?

actually my teacher said so to assume so by tht i told so becoz in pst pprs 2-3 similar questions use the same assumption

 

[NinjaInPyjamas]

These are factual answers they dont really have any explanation

yeah, I wanted the factual answers. what reaction is it, and how to complete the reactions.

 

[chocolate_girl]

there is a seperate threads that creep up for the practical see them and one piece of advice I can give what ever you do keep calm cause in 1 hour 30 min there is no recovery time

Its 2 hours in practical

 

[chocolate_girl]

a free radical has one unpaired valence electron which gives it high reactivity.
to make CaSO4 from Ca(NO3)2, you will need a soluble (otherwise no reaction will occur as the salt will not dissolve) salt that has a metal(X) cation that can displace Ca to form XNO3 and a sulfate anion to replace NO3
Sodium Sulphate would do the job.
again the same kind of question. any soluble sulfate salt would do the job. sodium sulfate is, i am sure, soluble.
we have studied in hydroxy compounds chapter that -OH can be replaced by a halogen with help of PCl3 or PCL5 or red phosphorus+halogen(I2, Br2 etc) + acid + heat
that will replace OH group.
CH3(CH2)4CH(Cl)CH=CHCHO

Isnt the salt in second one CaCl as they have referred to reaction 1 and formation of CaCl is reaction 1
Also in the last one why dont we add Cl in double bonds?

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_23.pdf in Q3 a-ii) how do we know what is the shape?

 

[chocolate_girl]

yeah, I wanted the factual answers. what reaction is it, and how to complete the reactions.

The mark scheme would say it all

 

[AbbbbY]

These are factual answers they dont really have any explanation

Everything, my dear Watson, has a logical explanation.

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_21.pdf

q4 (c) (d) (e) can someone explain in detail please?

c)
S into T is hydration so I'd use steam + phosphoric acid catalyst @ 300C
S into U is di-ol so Cold Dilute Acidified KMnO4 in a heartbeat.
T into S is dehydration so I'd use conc H2SO4 @ 180C [Can also use H3PO4 @ 300C but that's not recommended]

T with Na (excess).
Replace all the OH's with O-+Na
NaOOCCH(ONA)CH2COONa

U with Na2CO3 (excess)
Replace the carboxylic OH's with O-+Na but not the alcohol OH's.

NaOOCCH(OH)CH(OH)COONa

Add the +'s and -'s on top. Was making it look all weird in typed format since I can't superscript it here.

e)
It's merely asking for cis trans isomers.

cis will be both COOH's on the same side of the two carbons and trans will be diagnol/opposite sides of the two carbons. If this doesn't make sense let me know and I'll draw it out for you.

why this sequence

Don't you know how to make protein chains from tri-peptides? You gotta join the chain in such a way that it forms the shortest chain with each tripeptide being used. You've to basically connect the dots. See where they overlap.

gly-ala-gly
ala-gly-ser
ser-val-lys

I'm taking these three as a random self created example. I state that the N terminal is glycine.

So, gly-ala-gly to begin with.
Now I'll see if I have tri-peptides starting with ala-gly or just gly and it's basically hit-and-trial and some logical thinking after this. Ofcourse, I don't have to repeat the common aminoacids. Like gly-ala-gly, second tripeptide is ala-gly-ser but I already have ala-gly ending the first tripeptide so my polypeptide with these 2 would be gly-ala-gly-ser

so, gly-ala-gly-ser-val-lys would be my polypeptide.

Soo sorry for the crappy explanation. I know I can do better because I've taught a lot of people how to do this but that involved a paper + vocal communication.

 

[AbbbbY]

okay.I see some things in chemistry are not very logic based

Wrong! Everything in every science is fully logic based. We, students, tend to ignore the logic in finding shortcuts/ways things are easy for US to remember/explain.

 

[AbbbbY]

I know its because of the size.But why? :/

Two words: Steric Hindrance!