All chemistry Doubts here :)

[PUSHPAK1321]

I asked the wrong question,the paper is same but i want the answer for the 11th question srry guys i posted the wrong question number

HyDraZin3, I guess markscheme is complicated, the best way, is to try balancing the equation, keeping in mind co-efficent of hydrocarbon is 1, for Oxygen it is 2. The only variation must be on the product side. Usually such question either have answer as A) or B), to keep it simple for candidates.
So try for answer B:

C6H9OH + 8O2 => 6CO2 + 5H2O EQUATION IS BALANCED

Hope u understood.

Good Luck.

 

[HyDraZin3]

THANKS a lot, i understood what u said

 

[Abid357]

Salaams,

http://www.xtremepapers.me/CIE/index.ph ... _qp_03.pdf

Qns. 4 (b) (ii) and (iii) of Second Variant... I'm not getting the correct mole ratio somehow, could anyone please do the working for me?

Jazakum Allah.

 

[HyDraZin3]

K,see
In 4 (b) (ii) they are asking the mole ratio so work out the number of moles for carbon and hydrogen
they say that benzene is composed of 92.3% of carbon so therefore number of moles of carbon=92.3/12=7.7Moles
then the amount of hydrogen is 7.7% so the number of moles of hydrogen=7.7/1 =7.7
Therefore the mole ratio=7.7:7.7
=1:1
4 (b) (iii) For the emperical formulae as we have worked out the mole ratio, the formulae would be CH
For the molecular formulae, they have said that the molecular mass of benzene is 78.To work out the molecular formulae we should divide the molecular mass by the empercial mass
So the emperical mass=12+1=13 (CH)
so 78/13=6
Therefore molecular formulae=6* (CH)
=C6H6
I hope u have understood it

 

[Abid357]

Ohhh the atomic mass for Carbon was 12 ! And I thought it was 16 >_<''

Thanks so much pal. Wow, you're really good at explaining

 

[HyDraZin3]

 

[xIshtar]

I have one more doubt :bad:
http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf
Question 3 and question 21

In question 21 can someone explain me the answer by writing reactions?

If you still don't get these, I'll explain now:

Question 3, NaCl is a salt, and thus is neutral. When you dissolve something in a pure substance, it's melting and boiling point change, so it is B.
Question 21, relies on your cation tests, which are essential for the paper we have already done. Basically, Sodium hydroxide gives a Green ppt. when added to Iron(ii) and a Pale Blue ppt. when added to Copper(ii)
Thus the answer is C..

If anyone has any other Paper 1/Paper 3 doubts, I'll do my best to help

 

[HyDraZin3]

I have a doubt about oxidation and reduction.
Fe2O3 +3CO->2Fe +3CO2

Here only oxidation state of Fe is reducing from 3 to 0 but the oxidation state of O3 which is -2 remains the same but then too is it like the whole Fe2O3 is reduced and is this the case in all reactions? :unknown:

 

[HyDraZin3]

But the Nacl is not dissolved in water i think and cant the melting point be less than 100 degree celsius?

 

[xIshtar]

But the Nacl is not dissolved in water i think and cant the melting point be less than 100 degree celsius?

I read the wrong questions xD... My bad.. For that question 3.. The answer is still B, but it is because the NaCl will cause the melting point and boiling point to rise above 100C.. And in addition as it is an ionic compound it's MP and BP are likely to be quite high.

As for Question 21, the answer is C because the test is that for nitrates..

I have a doubt about oxidation and reduction.
Fe2O3 +3CO->2Fe +3CO2

Here only oxidation state of Fe is reducing from 3 to 0 but the oxidation state of O3 which is -2 remains the same but then too is it like the whole Fe2O3 is reduced and is this the case in all reactions? :unknown:

I don't quite understand what you are asking, the Fe is being reduced and the CO is being oxidised, so it is a redox reaction. The CO is the reducing agent as it gets oxidised and it causes the reduction of something else, the iron.

 

[HyDraZin3]

Yaa,only Fe is getting reduced but the answer is the whole Fe2O3 will reduce and is this the case in other reactions also?

 

[xIshtar]

Yaa,only Fe is getting reduced but the answer is the whole Fe2O3 will reduce and is this the case in other reactions also?

Yes, I get what you are saying now.. You have to say the entire reactant getting oxidised.. Ie, if it was ZnO, then you would say the Zinc Oxide was reduced rather than just the Zn.

 

[HyDraZin3]

So if in ZnO, only Zn is getting reduced and if Oxygen neither gets oxidised nor reduced, then too we should write that the whole ZnO is getting reduced?

 

[xIshtar]

So if in ZnO, only Zn is getting reduced and if Oxygen neither gets oxidised nor reduced, then too we should write that the whole ZnO is getting reduced?

Yeah, don't just say that the Zinc is getting reduced, because it's not necessarily true as Zinc alone cannot be reduced.. Zinc Oxide however can, so you write ZnO is being reduced.

 

[HyDraZin3]

K,thnx a lot

 

[xIshtar]

K,thnx a lot

No problem, if you need anything else, just post here xP

 

[haochen]

ｏｈｈ　ｉｍ　ｏｕｔ　ｏｒ　ｏｎｌｙ　３　ｄａｙｓ　ａｎｄ　＊ｂａｎｇ＊　ｆｕｌｌ　ｏｆ　ｓｕｐｐｏｒｔｅｒ (especially xIshtar)
no offence：）

 

[Divalicious]

Guys I was wondering what did you do for the last question in paper 6 variant 1, where it says what happens when the cleaning liquid is added to a sink containing a fizzy drink?
I wrote that fizzy drinks contain carbonic acid which will react with the cleaner and release/liberate chlorine which is a toxic gas [as it was mentioned in the question]. But some of my friends have been saying that will explode and other stuff like that....anyone got a confirmed answer?

 

[haochen]

ｎｅｕｔｒｌｉｚａｔｉｏｎ　ｒｅａｃｔｉｏｎ　ｏｃｃｕｒ　ｓｏ　ａｎｙｔｈｉｎｇ　ｒｅｌａｔｅｄ　ｔｏ　ｉｔ　ｉｓ　ｃｏｒｒｅｃｔ　ｅｖｅｎ　ｕｒｓ　：Ｄ

ｈｏｐｅ　ｕ　ｇｏｔ　ｉｔ

 

[HyDraZin3]

I have a doubt
1.http://www.xtremepapers.me/CIE/Cambridg ... _qp_12.pdf
Question (14)
I think chlorine will go to anode (yellow green) and hydrogen at cathode (colourless) because it is concentrated NaCl but the answer is something else
2.http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_1.pdf
Question 15

THANKS