Chemistry: Post your doubts here!

[Scafalon40]

need explanations to some questions in paper 1 nov/oct 10..
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_11.pdf

Q7....why is it C and not D
Q10

Angle 1)109.5
Angle 2)120
Angle 3)104.5
For Q10
It forms a quadratic equation
The answers are 4 and 2/3

 

[iKhaled]

Angle 1)109.5
Angle 2)120
Angle 3)104.5
For Q10
It forms a quadratic equation
The answers are 4 and 2/3

for question 10 ik that it has something to do with algebra but can u please show me the work out if u dont mind bro..?

 

[Scafalon40]

for question 10 ik that it has something to do with algebra but can u please show me the work out if u dont mind bro..?

You'll have to wait a little: busy but i'll post in a few minutes

 

[Scafalon40]

lets do this, i'll need your input too because you'll learn it better...
What are the initial moles?
1,1,0,0 ( form the equation for the reaction)
what are the equilibrium moles?
1-x,1-x,x,x
What is the expression for the Kc?
What is the value of Kc?
Ring a bell?

 

[kagome]

can anyone teach me how to obtain the formula of compound through NMR please? Chemistry A2 Section B

 

[Jaf]

Look at the equation even more closely, option A is that HSO3^- is acting as a base.

Sorry, I was explaining it right but I miswrote the ions.
They show the products as ions, but what is really forming is H2SO3. HSO3- is accepting protons to form H2SO3. SO3 (2-) is the ion acting like an acid.

 

[geek101]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf Q5, please explain! thank you

 

[Scafalon40]

Sorry, I was explaining it right but I miswrote the ions.
They show the products as ions, but what is really forming is H2SO3. HSO3- is accepting electrons to form H2SO3. SO3 (2-) is the ion acting like an acid.

Electrons...wait, aren't we supposed to answer in terms of protons?

 

[étudiante]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf Q5, please explain! thank you

i think its B
A- not possible because electrons will first fill up singly in subshells
B- after single filling-up, the last e- is in the 2p sub-shell
C- for low-energy state, 3p sub-shell needs 2 be filled-up first
D- excited state (they want low energy so not possibe)

 

[Jaf]

Electrons...wait, aren't we supposed to answer in terms of protons?

Ugh sorry, again. I haven't had my daily cup of tea. There's too much on my mind at the moment (exams?).

I meant protons.

 

[Jaf]

Wait... so lemme take everything from the top so there's no confusion.
Reaction 1:
This does not seem to have an acid/base in it.
However, we do know from our knowledge about the use of SO2 as a preservative that it acts as a reducing agent (so B is eliminated) and also makes food acidic.

Reaction 2:
HSO3- in the base. H+ is the acid.
H2SO3 is the product. So in effect, HSO3- is accepting a proton making it act like a base.
Remember how adding SO2 made food acidic? H2SO3 is what does this.

I hope I've gotten everything correct this time.

 

[Scafalon40]

Ugh sorry, again. I haven't had my daily cup of tea. There's too much on my mind at the moment (exams?).

I meant protons.

Um...yeah... well done Jaf; you have me throughly confused!

 

[étudiante]

Wait... so lemme take everything from the top so there's no confusion.
Reaction 1:
This does not seem to have an acid/base in it.
However, we do know from our knowledge about the use of SO2 as a preservative that it acts as a reducing agent (so B is eliminated) and also makes food acidic.

Reaction 2:
HSO3- in the base. H+ is the acid.
H2SO3 is the product. So in effect, HSO3- is accepting a proton making it act like a base.
Remember how adding SO2 made food acidic? H2SO3 is what does this.

I hope I've gotten everything correct this time.

YES! done nice n neat! thanx boss!

 

[Scafalon40]

Wait... so lemme take everything from the top so there's no confusion.
Reaction 1:
This does not seem to have an acid/base in it.
However, we do know from our knowledge about the use of SO2 as a preservative that it acts as a reducing agent (so B is eliminated) and also makes food acidic.

Reaction 2:
HSO3- in the base. H+ is the acid.
H2SO3 is the product. So in effect, HSO3- is accepting a proton making it act like a base.
Remember how adding SO2 made food acidic? H2SO3 is what does this.

I hope I've gotten everything correct this time.

Strange explanation, lemme think over it....

 

[Scafalon40]

Strange explanation, lemme think over it....

Kinda makes sense now, I think...
A lot of thinking for one mark though, damn CIE

 

[Scafalon40]

Thanks Jaf, I've been at this for quite some time now; finally solved!

 

[iKhaled]

lets do this, i'll need your input too because you'll learn it better...
What are the initial moles?
1,1,0,0 ( form the equation for the reaction)
what are the equilibrium moles?
1-x,1-x,x,x
What is the expression for the Kc?
What is the value of Kc?
Ring a bell?

ting ting ting..thats what my brain responded..got it now thank uuuu bro u owwwnn

 

[Scafalon40]

ting ting ting..thats what my brain responded..got it now thank uuuu bro u owwwnn

Nice one

 

[Scafalon40]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf
Q34
Ans b
Why is statement 3 false?
Ca ions will react with carbonic acid to give CaCO3, no?

 

[Jaf]

Can ethene be polymerized in a single reaction or no?
I remember seeing a question that tests the knowledge of this twice (maybe more) and now I can't remember the answer.