Biology; Chemistry; Physics: Post your doubts here!

[Abdul Hanan]

About the last line, the statement is incorrect. We have added the KMnO4 in excess (KMnO4 is purple in colour), and as a result, the solution has turned purple

it is added till the "end point",which i think makes KMnO4 not in excess......
but do tell me how it is in excess if i am incorrect.......

 

[FLRNAB]

http://papers.xtremepapers.com/CIE/...l O Level/Chemistry (5070)/5070_w10_qp_41.pdf
Question 8 . Part J <-- Help
(f) = 2.23x10^-2
(i)=1.58x10^-1

 

[asadalam]

it is added till the "end point",which i think makes KMnO4 not in excess......
but do tell me how it is in excess if i am incorrect.......

End point is the exact point when the indicator changes color,so in this case at the end point,it would be in excess and show its color

 

[Mahnoorfatima]

By the way when we're calculating that CxHy thing , we will always consider H diatomic. ? The Mr has to be 14 in total? Always???

 

[funky brat]

By the way when we're calculating that CxHy thing , we will always consider H diatomic. ? The Mr has to be 14 in total? Always???

No, you won't, you don't know the value of y.

 

[funky brat]

End point is the exact point when the indicator changes color,so in this case at the end point,it would be in excess and show its color

I don't really get this thing. End point is the exact point when the acid/ alkali has been neutarlised but when we write the colour we consider it in excess. :/

 

[funky brat]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w10_qp_41.pdf
Question 8 . Part J <-- Help
(f) = 2.23x10^-2
(i)=1.58x10^-1

Wait.

 

[Abdul Hanan]

End point is the exact point when the indicator changes color,so in this case at the end point,it would be in excess and show its color

i agree

 

[Faizan Muhammmad]

green/yellow/colourless- to- purple
as the solution(P) in flask is very dilute it will show a very light colour (a mixture of the fe 2+ and fe 3+ ions) its not red-brown or dirty green as solution DILUTE.
when potassium manganate(VII) is added, the solution changes colour as potassium manganate in excess.

to yellow kaisay hua?

 

[exploded diper]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_w10_qp_41.pdf
Question 8 . Part J <-- Help
(f) = 2.23x10^-2
(i)=1.58x10^-1

so u see we have moles for iron sulphate which are (f)
we have moles of water which are (i)
this (i)moles are for this(f)moles...and we need water moles for one feso4.......
so divide (1) by (f) which cums to be 7.18.....so round it of to 7.......

 

[asadalam]

I don't really get this thing. End point is the exact point when the acid/ alkali has been neutarlised but when we write the colour we consider it in excess. :/

Yes,it changes color as acid/alkali goes into excess.We cant stop at the exact moment when its neutralized,there is still a small amount that is present and even that small amount would be in excess.

 

[exploded diper]

I don't really get this thing. End point is the exact point when the acid/ alkali has been neutarlised but when we write the colour we consider it in excess. :/

mostly yes....

 

[Mahnoorfatima]

No, you won't, you don't know the value of y.

Whaaaaat? Check out Question 8 part L .Why are we taking the MR as 14 then? http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s07_qp_4.pdf

 

[Mahnoorfatima]

C ---H
12 + 2 =14
always divide by 14

Theres ALWAYS a CH2 group difference so CxHy will ALWAYS be 14 hence H will be twice of C.. the two types are :
e.g 1) CxHy = 128
x will be 8 H will be 16
e.g 2) H2NCxHyCOOH = 145
CxHy= 145 - (mass of H2NCOOH)
x=6 H=12
ALWAYS divide by 14 when it comes to CxHy
we even use this technique to find number of carbon atoms

*CH2 sorry my bad .. It's CH2
FUNKY BRAT! See we have to take CH2 . But I dont get why! :'(

 

[kirann]

He gets frightened or shocked so adrenaline is secreted which causes the heart to pump faster so that oxygen and glucose could go faster to the muscles..

Whats the need for oxygen and glucose to be pumped faster to muscles?

 

[Abdul Hanan]

to yellow kaisay hua?

yellow is in marking scheme because very little fe3+ ions presant which instead of giving red-brown, will give yellow as they are very less (DILUTE SOLUTION)

 

[exploded diper]

Whaaaaat? Check out Question 8 part L .Why are we taking the MR as 14 then? http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_4.pdf

u can take the formula c ( N) h 2 (N)
so y is equal to two x......

 

[exploded diper]

Whats the need for oxygen and glucose to be pumped faster to muscles?

so the person can use it for fight or flight....

 

[Maganius]

yellow is in marking scheme because very little fe3+ ions presant which instead of giving red-brown, will give yellow as they are very less (DILUTE SOLUTION)

Right

 

[exploded diper]

yellow is in marking scheme because very little fe3+ ions presant which instead of giving red-brown, will give yellow as they are very less (DILUTE SOLUTION)

which question are u guys talking about...