Physics, Chemistry and Biology: Post your doubts here!

[GorgeousEyes]

for Q.36 it is D u need to memorize the structures of all hydrocarbons, it cant be explained :/
for Q.40 it is D also because u need to memorize the conditions of the reactions u take, none of these questions can be explained, it can only be memorized

First question , I think it should be anaerobic , so how the cotton wool is used?
Second one , Alkene is unsaturated right ? so how after it polymerized it become saturated ? , cause there is no double bond any more ?

 

[joulie]

Can u explain this to me plz
Biology nov 2009 Q22 why is the answer A not B i thoght its B bcause glucose and protein concentations are 00 in urine.

 

[Abu mota]

First question , I think it should be anaerobic , so how the cotton wool is used?
Second one , Alkene is unsaturated right ? so how after it polymerized it become saturated ? , cause there is no double bond any more ?

srry i think i got the wrong paper :/ rlly srry
for Q.36 it is B and yes it became saturated because there is no double bond anymore and remember its name is poly(ethene)
for Q.40 the cotton wool is used to allow the CO2 to escape without oxygen entering, we dont use a bung because it will cause the build up of CO2 and it is anaerobic respiration

 

[Abu mota]

Can u explain this to me plz
Biology nov 2009 Q22 why is the answer A not B i thoght its B bcause glucose and protein concentations are 00 in urine.

the first column is just to confuse you so leave it, look at the second and the third column and u will find that only glucose and water decrerase while the others dont and so the answer is glucose and water which is A.

 

[GorgeousEyes]

srry i think i got the wrong paper :/ rlly srry
for Q.36 it is B and yes it became saturated because there is no double bond anymore and remember its name is poly(ethene)
for Q.40 the cotton wool is used to allow the CO2 to escape without oxygen entering, we dont use a bung because it will cause the build up of CO2 and it is anaerobic respiration

thank you

 

[Abu mota]

Guys, can you explain to me q 19 and q 22:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf

for Q.19 this isnot an redox reaction and so the oxidation numbers stay the same but the pH increase because the alkali increase the pH.
for Q.22 it is D because zinc is actually not soluble in water and the only way in which u use liquids is in titration reaction and this isnt one

 

[Yousif Mukkhtar]

for Q.19 this isnot an redox reaction and so the oxidation numbers stay the same but the pH increase because the alkali increase the pH.
for Q.22 it is D because zinc is actually not soluble in water and the only way in which u use liquids is in titration reaction and this isnt one

I got it thanks.

 

[Abu mota]

for Q.19 this isnot an redox reaction and so the oxidation numbers stay the same but the pH increase because the alkali increase the pH.
for Q.22 it is D because zinc is actually not soluble in water and the only way in which u use liquids is in titration reaction and this isnt one

and also for Q.19 u can check it if u want for K2Cr2O7 the oxidation state is -14 and K is 2+ and in order to cancel them u need +12 divided by 2 and Cr will have an oxidation state of 6. then for K2CrO4 oxidation state of oxygen is -8 while K 2+ and so to balance them u need +6 and so the oxidation state of Cr didnt change.
if u dont understand how i get these numbers, ask and i will explain it more

 

[Yousif Mukkhtar]

and also for Q.19 u can check it if u want for K2Cr2O7 the oxidation state is -14 and K is 2+ and in order to cancel them u need +12 divided by 2 and Cr will have an oxidation state of 6. then for K2CrO4 oxidation state of oxygen is -8 while K 2+ and so to balance them u need +6 and so the oxidation state of Cr didnt change.
if u dont understand how i get these numbers, ask and i will explain it more

Nah that wasn't the big problem, I found out that vi is same on both sides. The pH part confused me though.

 

[always-smile :)]

PLLZ i need an explanation for this question
p1 chem oct 2008 q-11 (( why B ))

 

[joulie]

the first column is just to confuse you so leave it, look at the second and the third column and u will find that only glucose and water decrerase while the others dont and so the answer is glucose and water which is A.

i see thanks

 

[Ahmed Khider]

PLLZ i need an explanation for this question
p1 chem oct 2008 q-11 (( why B ))

Carbon is in group 4 so its valency is 4.Chlorine is in group 7 so its valency is 1. Now cross the 2 valencies and u get CCl4

 

[Abu mota]

PLLZ i need an explanation for this question
p1 chem oct 2008 q-11 (( why B ))

carbon has a valency of 4 (as it is in group 4) but Chlorine has a valency of 1 (group 7) and so u write something like C4 Cl1 and u exchange the numbers and u will get CCl4 which is B. if u dont understand ask again

 

[always-smile :)]

ooops i'm sorry i mean 2007
thnx for explaining that anyway

 

[Yousif Mukkhtar]

ooops i'm sorry i mean 2007
thnx for explaining that anyway

Try a balanced equations for each compound till you get 802.


For B:
C6H90H + 802 -----> 6CO2 + 5H20

So one molecule of C6H0OH reacted with eight molecules of oxygen.

 

[Yousif Mukkhtar]

Can someone explain q 17:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_1.pdf
Shouldn't increased particle size speed up a reaction?

 

[always-smile :)]

Try a balanced equations for each compound till you get 802.


For B:
C6H90H + 802 -----> 6CO2 + 5H20

So one molecule of C6H0OH reacted with eight molecules of oxygen.

thnx

 

[always-smile :)]

Can someone explain q 17:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_1.pdf
Shouldn't increased particle size speed up a reaction?

when the particle size increase the reaction become difficult so it slows down the reaction

 

[Yousif Mukkhtar]

when the particle size increase the reaction become difficult so it slows down the reaction

Oh okay, thanks.

 

[always-smile :)]

Oh okay, thanks.

any time