Physics, Chemistry and Biology: Post your doubts here!

[areebaization]

yeah but y 2Ag?

tin mostly ionizes with the oxidation state +2, and Ag has the valency +1.
In order to replace the silver ions tin has to donate two electrons to silver.
these two electrons r accepted by 2 silver ions. Read the eqn. again. Hope u get the point!

 

[sma786]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_03.pdf
Question 7 , a - i ..

 

[thats_me]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_03.pdf
Question 7 , a - i ..

C4H10 +6.5O2 --->4CO2 +5H2O
ratio =1 : 6.5 :4 : 5
Volume of oxygen =( 1 : 6.5) ratio for butane : oxygen , so used oxygen can be found by cross multiplying i.e if 1=10 , thn 6.5 is how much,(10*6.5) u get 65 ,thn for left oxygen 100-65=35
volume of CO2 = (1 : 4)ratio of butane : cO2 , again cross multiply i.e if 1=10, thn 4 is how much? (4*10)u get 40

 

[areebaization]

C4H10 +6.5O2 --->4CO2 +5H2O
ratio =1 : 6.5 :4 : 5
Volume of oxygen =( 1 : 6.5) ratio for butane : oxygen , so used oxygen can be found by cross multiplying i.e if 1=10 , thn 6.5 is how much,(10*6.5) u get 65 ,thn for left oxygen 100-65=35
volume of CO2 = (1 : 4)ratio of butane : cO2 , again cross multiply i.e if 1=10, thn 4 is how much? (4*10)u get 40

how did u get 1:10? and do we have to convert cm^3 to dm^3?

 

[thats_me]

how did u get 1:10? and do we have to convert cm^3 to dm^3?

from the question hun! 10 cm3 of butane s mixed with.... no we dont the ans is also in cm3 so no need for conversion..

 

[areebaization]

from the question hun! 10 cm3 of butane s mixed with.... no we dont the ans is also in cm3 so no need for conversion..

haha I got confused cause it said the o2 was in Excess
Thanx again

 

[thats_me]

haha I got confused cause it said the o2 was in Excess
Thanx again

hehe HAppens!

 

[sma786]

C4H10 +6.5O2 --->4CO2 +5H2O
ratio =1 : 6.5 :4 : 5
Volume of oxygen =( 1 : 6.5) ratio for butane : oxygen , so used oxygen can be found by cross multiplying i.e if 1=10 , thn 6.5 is how much,(10*6.5) u get 65 ,thn for left oxygen 100-65=35
volume of CO2 = (1 : 4)ratio of butane : cO2 , again cross multiply i.e if 1=10, thn 4 is how much? (4*10)u get 40

where'd you get the 10 and 100 from?

 

[thats_me]

where'd you get the 10 and 100 from?

frm the questionnnn butane 10 cm3 <--limiting reagent ,Oxygen 100cm3 <--- in excess , so we use the limiting reagent to find the used oxygen

 

[sma786]

frm the questionnnn butane 10 cm3 <--limiting reagent ,Oxygen 100cm3 <--- in excess , so we use the limiting reagent to find the used oxygen

ooh oh lol sorry

 

[sma786]

how to express a double bond in a covalent diagram ??
for example , O=C-Cl2

 

[kainat husain]

what values :S
bii higher pressure favours to the side with fewer moles causing the equilibrium position to shift right
biii they can be used again by passing over the heated catalyst

(II) high pressure favors the side with lowest number of moles so increasig pressure will favor the production more ammonia
(iii)i think the remaining h2 andn2 are fed back into the proccess to produce more ammonia.....u do not need to take any values just use ur knowladge the table was just there to help u remember!

because the higer the pressure the more ammonia is formed as they are squashed together more....due to less space the hydrogen and nitrogen have to join up as there is no space for them to move along by themselves...

sorry guys i wasnt askin abt this question paper i m askin abt this
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s03_qp_6.pdf
q- 4 b- (ii) (iii)

 

[sma786]

sorry guys i wasnt askin abt this question paper i m askin abt this
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s03_qp_6.pdf
q- 4 b- (ii) (iii)

lol hahahah xD

 

[areebaization]

sorry guys i wasnt askin abt this question paper i m askin abt this
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s03_qp_6.pdf
q- 4 b- (ii) (iii)

Since in part b i) It says that the pin turns 90 degree (which is 1/4 of a circle) so in part b ii) we will divide the circumference of the heated pin by 4 (to get 1/4th of the circumference, which is the expanded length) then in the next part (iii) we will add this value with the original length of the rod, making sure that the units r the same.
Here are the worked out answers:
bi) 3.8mm
bii) 3.8/4=0.95 mm
biii) 0.95mm+0.75m=
0.00095 + 0.750 = 0.75095m

 

[NIM]

I hope now u'll get it a lil better ..

thnx a lot dude!!!
if i hav any other question lyk this i'll ask u...

 

[AAnsarii]

can some1 tell me wat exactly PARALLAX error is..coz it alwayz cums in d physics ppr...i noe its a dum qs but plzzz..!!

hey, sir said parallax error was to not look straight at where (eg) d level of liquid is in a measuring cylinder
hope u got it..
all d best

 

[AAnsarii]

Can i get a good definition of equilibrium ?

rate of 4wrd rxn= backward rxn
concentrations do not change, n dey say dat macroscopic prop. dont change, what dat means, the Lord knows best.

 

[AAnsarii]

CAN SBY PLZ XPLAIN WHAT IS macroscopic properties?? i'll iA be v greatful
Thank u in adv.

 

[Stormcry72]

Sn + 2Ag2+ ----> Sn2+ + 2Ag

it should be 2Ag+, not 2+
2Ag2+ means Ag lost 4 e-, not 2
and in this case it should lose 2 e-

 

[EpicLol]

The grade boundries are getting lower every year so I'm guessing it would be an A this year
If you're aiming for an A* in the end you have to get a max of 3 faults in paper 1, 10 in paper 3 and 5 in paper 6 ( my teacher told me this)

I think yr teacher tried to simplify this and explain it to u....90 or higher for A* is not the percentage....the percentage is taken and compared to the rest of the world, then the number is decided and if u get more than 90 its an A*...

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w11_gt.pdf look at the bottom part as well for an idea on how to get A*....u have a margin of usually of 160/200 or higher is A*