All chemistry Doubts here :)

[xIshtar]

it's 6. but can i know why?

I did 4+7 = 11/2 5.5.. But the answer is 6, they expect you to know that? Question please..

See what i think is, if H and OH will go from both sides, the polymer should be :- -OC-C6H4-COOCH2CH2-0-
My polymer is correct, but in the mark scheme they are adding one more O in the start :- -OOC-C6H4-COOCH2CH2-0- and i dont understand why there is this addition :unknown:

You have taken too much OH off.. OH only comes off one end, the H just comes off the other end as there is a continuation..

It may be easier if you draw the structural formula, I find it easier that way. I'll draw it on paint.

 

[JmCullen]

that's the question. but it's MCQ.. paper 1..
i just want to know.. in case they ask in paper 3..

 

[JmCullen]

another question..

http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf

question 29..
how did you know the starting volume???

 

[xIshtar]

another question..

http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf

question 29..
how did you know the starting volume???

Estimate it using what percentage of air is oxygen, as it is used for the formation of the rust.. I'd say 150cm^3
As oxygen is 20 something percent of air. So C.

 

[zkapoor]

JmCullen - Since the amount of water added is unknown, I reckon that the answer lies in the range 5-7. Since 6 is the midpoint of the two the mark scheme probably says that but I think fluctuation around the value should be fine

 

[xIshtar]

I'd just like to apologise for my poor drawing above

If anyone needs help, I'll do my best

 

[HyDraZin3]

Here u have to apply ur math knowledge.
In air there is 20% of oxygen.
So therefore 80% of x =x-30 (x is the total air)
80x=100x-3000
-20x=-3000
x=150cm^3

You can also cross-check ur answer
80% of 150=120
150-120=30
Therefore 30cm^3 is reduced

 

[xIshtar]

Here u have to apply ur math knowledge.
In air there is 20% of oxygen.
So therefore 80% of x =x-30 (x is the total air)
80x=100x-3000
-20x=-3000
x=150cm^3

You can also cross-check ur answer
80% of 150=120
150-120=30
Therefore 30cm^3 is reduced

Read my solution to your problem?

 

[HyDraZin3]

Hey, u added a O at the last but from where that O came?

 

[JmCullen]

Thanks guys, for helping my questions..
i get it already.
appreciate it!

Good luck to all of you in chemistry!

*i might still have loads of questions. haha*

 

[xIshtar]

Hey, u added a O at the last but from where that O came?

I showed you in the diagram.

 

[lychee26]

18 Which statement about bromine is correct?
A Bromine is insoluble in non-polar solvents.
B Bromine vapour is more dense than air.
C Bromine will not vapourise significantly under normal conditions.
D Gaseous bromine is purple.

 

[xIshtar]

18 Which statement about bromine is correct?
A Bromine is insoluble in non-polar solvents.
B Bromine vapour is more dense than air.
C Bromine will not vapourise significantly under normal conditions.
D Gaseous bromine is purple.

That was in an igcse paper? Link to the paper please

 

[HyDraZin3]

I saw it in the diagram but as H20 is eliminated from both sides, that O in the end should not be there but in the diagram it is there.Thats what i was asking in the previous post "From where did the O come from" :%)

 

[xIshtar]

I saw it in the diagram but as H20 is eliminated from both sides, that O in the end should not be there but in the diagram it is there.Thats what i was asking in the previous post "From where did the O come from" :%)

You don't eliminate H2O from both ends.. Basically, think of it as a neverending chain.. Eliminate H from both ends of the full chain, then eliminate the H2O in the middle.

 

[HyDraZin3]

Can u tell me where these things are written.. and in which book?

 

[gary221]

y only temperature decrease and not increase? and can u explain me the whole question step by step? :sorry:

since its an endothermic reaction, the temperature will decrease(as energy is being taken in from the surroundings)
also since the quantity of water has reduced the tamp change will be greater

 

[xIshtar]

Can u tell me where these things are written.. and in which book?

Not specifically in my book, if my diagram didn't help then... Page 235 - Chemistry for IGCSE 2009 edition - Roger Norris and Roger Stanbridge..

 

[lychee26]

http://www.xtremepapers.me/CIE/International A And AS Level/9701 - Chemistry/9701_w10_qp_12.pdf

Qestion 18.

 

[HyDraZin3]

i am not saying that ur diagram didnt help, but i didnt understand that H and OH thing, so i wanted to have a look at that book.
Do u have the pdf file of that book?