Biology; Chemistry; Physics: Post your doubts here!

[kirann]

Not much!! But in ur formula u convert it into dm^3 to solve further. But here u need to put in the values and voila!!

both methods are same bro i just stretched my working so that he may understand it better

 

[Ram97]

both methods are same bro i just stretched my working so that he may understand it better

 

[kirann]

plz show your working as well for the second question...and explain it too

 

[Abdul Hanan]

View attachment 41641 View attachment 41642
plz show your working as well for the second question...and explain it too

oxygen is 20% in air when a sample is 100cm^3 the oxygen in it is 20cm^3
so when air 80cm^3 then,,,, 80 x 20/100= 16 cm^3
so yea remaining gas = 80-16=64 cm^3

 

[FLRNAB]

how come the tota l is 250????

http://en.wikipedia.org/wiki/Copper(II)_sulfate

249.685 g/mol (pentahydrate)

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_w12_qp_42.pdf
Question 8 part L

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_w11_qp_42.pdf
last part of the paper?
Question 10 f part i. How come the moles are equal to the previous part??

 

[Fate0]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w12_qp_42.pdf
Question 8 part L

Mass of G is 132.
Sum of all elements in G needs to be 132.
Subtract the known elements with coefficients from 142, that is 90.
132 - 90 = 42
CxHy = 42
Hit and trial
12(3)+6(1) = 42.

Thus x = 3 and y =6

 

[Fate0]

View attachment 41641 View attachment 41642
plz show your working as well for the second question...and explain it too

It will be 64%.
As air contains 20% oxygen, this 20% reacts with iron.
20/ 100 x 80 = 16cm3
16cm3 of O2 reacts.
Remainder =80-16 = 64

 

[Mahnoorfatima]

Mass of G is 132.
Sum of all elements in G needs to be 132.
Subtract the known elements with coefficients from 142, that is 90.
132 - 90 = 42
CxHy = 42
Hit and trial
12(3)+6(1) = 42.

Thus x = 3 and y =6

Where did 90 come from?

 

[FLRNAB]

Where did 90 come from?

2 Carboxyl Groups
C - 12 x 2 = 24
H - 1 x 2 = 2
O - 16 x 4 = 64

64+2+24 = 90

 

[FLRNAB]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w11_qp_42.pdf
last part of the paper?
Question 10 f part i. How come the moles are equal to the previous part??

Same as (E 250cm) because adding water does not add any more moles of ethanoic acid but only changes the concentration so moles would remain same. The answer is the same as "Part E"

Or start reading from this post

 

[Muhammad_Hamza]

please help me in this part?
For 3 marks.

 

[Hazel-logy]

Guys i need help pleaseee http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s04_qp_4.pdf
Question 9 last one

 

[Mahnoorfatima]

2 Carboxyl Groups
C - 12 x 2 = 24
H - 1 x 2 = 2
O - 16 x 4 = 64

64+2+24 = 90

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_w11_qp_42.pdf
How to calculate the last part? :/

 

[Mahnoorfatima]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_s12_qp_42.pdf
Last two parts... ????

 

[Ram97]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s12_qp_42.pdf
Last two parts... ????

For part (d) 35g/50cm^3 is 70g/100cm^3
From your graph where solubility is 70g/100cm^3 u find the temperature

For part (e) you find the solubility when temperature is 50
Then subtract both the solubulities i.e 150 - (whatever answer u get)
You'll find the mass which crystallises out

 

[Dark Destination]

How to prepare for Chemistry? :/

 

[kirann]

It will be 64%.
As air contains 20% oxygen, this 20% reacts with iron.
20/ 100 x 80 = 16cm3
16cm3 of O2 reacts.
Remainder =80-16 = 64

y 80-16 ?

 

[Qasim Hafeez]

Hey friends,
Today I had my physics exams at my school. The subject was really easy and I got a straight 'A' in the first term with only 2/3 marks short of a 'A*'
I find the subject easy, and did score good marks at test, but today everything seemed so difficult. I studied late night, and checked everything from past papers but in my exam papers the questions were so twisted I didnot know what to do.

Please any suggest how to improve.