Chemistry: Post your doubts here!

[♣♠ Magnanimous ♣♠]

Can someone please explain protonation??

protonation is addition of proton to an atom, molecule, or ion, forming conjugate acid.

 

[Raiyan3]

Can someone please thoroughly explain Question 5.a)
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_42.pdf

 

[saadgujjar]

lys-val-ser-ala-gly-ala-gly-asp ?

why this sequence

 

[MiniSacBall]

How does oxidation and reduction occur when ally alcohol is converted into propanal using a ruthenium catalyst

Actually with out catalyst you need two steps to convert ally alcohol into propanal, while when you use catalyst they both oxidation and reduction happens.
You won't be asked how but, but i guess ruthenium catalysis both reduction and oxidation so that's why you will get propanal, or else it won't make propanal.

 

[princeali97]

the marking scheme says it all
something like this
sorry coundnt do an exact drawing but i guess will now understand what the ms says

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

 

[sitooon]

Question 2c(iii)
Find PH

 

[goodluckayesha]

Question 2c(iii)
Find PH

pH of a buffer is pKa so apply the formula pH=pKa+log10(salt/acid)= 7.2+ log10(0.002/0.005) =6.8 understood?

 

[goodluckayesha]

Can someone please thoroughly explain Question 5.a)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_42.pdf

This stuff isn't in the syllabus or taught. This is precisely why it has shown you the 4 figures above the actual question. The examiner wants you to analyze those figures, see whats going on, and apply THAT to the question.

The question shows that all carbons in Benzene can be made to lie on the same plane, but not in cyclohexane. The question also shows that butane Carbons can be made to lie on the same plane, but methylpropane, also an alkane, cannot.
This tells us that if a compound has a ring, OR branching, it cannot be made to lie on the same plane.

All of them are co-planer apart from B.

C is coplaner because you don't have to consider the Oxygen atoms. The others are unbranched and two individual chains lying on the same plane.

 

[NinjaInPyjamas]

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

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

 

[chocolate_girl]

Help in following questions
1)http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_23.pdf
Question 3 a-ii)
2)http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_21.pdf
Question 3 d)
3)http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_22.pdf
Question 3 c)
4)http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_s11_qp_23.pdf
Question 4 c-ii)

Suchal Riaz

 

[chocolate_girl]

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?

These are factual answers they dont really have any explanation

 

[ZaqZainab]

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

Well i guess its cause Cl^- is smaller than I^-
So fitting 7 atoms of F around a Cl atom is difficult due to a lot of repulsion between the electrons.
But cause an I atom is bigger it can attach to 7 F atoms easily

this would make more sense
you know that electrons repel so more the place the have future away they will be and more the stable than being in tiny place
think of a lot of people in a car they would argue to get 1 full seat and no one to sit next to them but if you have a bigger car more places to sit....this is just an example

 

[princeali97]

this would make more sense
you know that electrons repel so more the place the have future away they will be and more the stable than being in tiny place
think of a lot of people in a car they would argue to get 1 full seat and no one to sit next to them but if you have a bigger car more places to sit....this is just an example

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

 

[sitooon]

pH of a buffer is pKa so apply the formula pH=pKa+log10(salt/acid)= 7.2+ log10(0.002/0.005) =6.8 understood?

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

 

[Suchal Riaz]

Help in following questions
1)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_23.pdf
Question 3 a-ii)
2)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_21.pdf
Question 3 d)
3)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_22.pdf
Question 3 c)
4)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_23.pdf
Question 4 c-ii)

Suchal Riaz

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

 

[Sijal Mirza]

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

 

[WaqarAhmedJamali]

why carboxylic acid does not undergoes nuclophilic addition by HCN

 

[sitooon]

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

P1 > 32-34 mostly
P2 > 48 &above

 

[MiniSacBall]

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

As sitoon said:
P1 > 32-34 mostly
P2 > 48 &above
But it also depends on number of other factors. Especially the marks curve or such in your area. If many people didn't score high marks or most of them have low marks then the curve will go down, i.e. you might need less marks to score an A in p1 it might be 25 or more.
Curse is like some sort of chart depending on your grade and all other candidates in your area grades/marks. If the average mark per candidate is low then the, marks for getting A will become low. If they are high, then for getting A you might need higher marks.

 

[AbbbbY]

As sitoon said:
P1 > 32-34 mostly
P2 > 48 &above
But it also depends on number of other factors. Especially the marks curve or such in your area. If many people didn't score high marks or most of them have low marks then the curve will go down, i.e. you might need less marks to score an A in p1 it might be 25 or more.
Curse is like some sort of chart depending on your grade and all other candidates in your area grades/marks. If the average mark per candidate is low then the, marks for getting A will become low. If they are high, then for getting A you might need higher marks.

According to the trend table I've drawn up on Excel from last year (updated it right now though), the average P1 A in the last 4 years is at 28.5 raw marks with a standard deviation of 2.03 while the average A in P2 in the same time is 44.8 with a standard deviation of 2.5. Both of which are easily achievable if you're thorough with your concepts btw.