Chemistry: Post your doubts here!

[asadalam]

i don't remember any such question like that ... mite have been from the ones i guessed ...
hw many eggshells had to be used in 2nd question?? ... i was just calculating and time was up so i simply chose 4 ...

It was 2.

 

[awesomaholic101]

It was 2.

ohh ... i am bad at guessing :/
last question was A rite?

 

[asadalam]

ohh ... i am bad at guessing :/
last question was A rite?

Yes

 

[Abdel Moniem]

The question with both an NH group and an ester group what was the answer for that?

 

[nehaoscar]

i don't remember any such question like that ... mite have been from the ones i guessed ...
hw many eggshells had to be used in 2nd question?? ... i was just calculating and time was up so i simply chose 4 ...

Me too p12! And even I got 4! Cause they make up 50%mass not the whole thing

 

[awesomaholic101]

Me too p12! And even I got 4! Cause they make up 50%mass not the whole thing

i didnt "get" 4 .. i guessed "4" coz it was the biggest no. .. but asadalam says it is 2?

 

[nehaoscar]

i didnt "get" 4 .. i guessed "4" coz it was the biggest no. .. but asadalam says it is 2?

Oh hahaha either ways others in my class also got 4 So i guess you guess may be correct

 

[awesomaholic101]

Oh hahaha either ways others in my class also got 4 So i guess you guess may be correct

Hopefully, In sha Allah.

 

[shazmina]

Sorry for the late reply, I doubt you need this anymore =P But, you only use the total abundance. For example if the relative abundance was 2 and 7, you will divide by 9.

Lol its okay ... thanks for the explanation

 

[jesse d]

Please help with this question
an aqueous solution contains 1 mol
of S2O32- ions and this reduces 4
mol of Cl2 molecules. What is the
sulfur containing product of this
reaction a) S (b)SO2 (c) SO32- (d)
SO42-. I cnt just come up with the
solution. Answer is D

 

[princess Anu]

Please help with this question
an aqueous solution contains 1 mol
of S2O32- ions and this reduces 4
mol of Cl2 molecules. What is the
sulfur containing product of this
reaction a) S (b)SO2 (c) SO32- (d)
SO42-. I cnt just come up with the
solution. Answer is D

for 1 mole of S203^2- to reduce 4 moles of Cl2 molecules it should give 8 electrons in order to form 8Cl^-
since there are two sulphur in S2O3^2- each sulphur atom gives 4 elecctrons
in S2O3^2- the oxidation number of sulphur is +2. since now sulphur is giving 4 electrons each, its oxidation number becomes +2+4=+6. So find the oxidation number of sulphur in each option & you'll realise only in D sulphur has a oxidation number of +6.

 

[jesse d]

how did you arrive at each sulfur atom giving 4 electrons. Thank you

 

[_MoHD_E]

can someone explain why it's D, and not the others
View attachment 55088

A cannot be an answer
B cannot be an answer because exothermic reactions do not require high temperature because exothermic reactions occur readily and at a fast rate unlike endothermic reactions
C cannot be an answer because breaking of a bond is an endothermic reaction not exothermic

 

[_MoHD_E]

http://onlineexamhelp.com/wp-content/uploads/2014/08/9701_s14_qp_11.pdf
Question 3.......Help please!!!!!!!! The Ans is D
My doubt is why cant the answer be C????

C says -2 x enthalpy change of formation of water
D says +2 x enthalpy change of formation of water
We multiply by +2 not -2

 

[Shahzaib Warraich]

Hey,
can anyone upload solved paper 5 questions(graph questions)

-the construction lines part that is and finding out the equations to be used.
thank you.

 

[qwertypoiu]

Hey,
can anyone upload solved paper 5 questions(graph questions)

-the construction lines part that is and finding out the equations to be used.
thank you.

Perhaps this will help you:
https://www.xtremepapers.com/commun...-a-level-paper-5-p5-solved-past-papers.41363/

 

[shinnyyy]

Oct Nov 2003 paper 1

Can anyone explain Q2,3,15 and 20 ??

 

[shinnyyy]

May June 11 paper 2 and variant 22.
can someone please explain Q1..c i. we get 0.04 moles of acid and alcohol,,dont we subtract it from 0.1 to get moles at equilibrium?

 

[Wkhan860]

Oct Nov 2003 paper 1

Can anyone explain Q2,3,15 and 20 ??

q2 is B
30%=mass of P2O5
? = mass of P2
cross multiply to get the answer

 

[fantastic girl]

Oct Nov 2003 paper 1

Can anyone explain Q2,3,15 and 20 ??

Q15 - see the ones which will decompose
B - MgCO3 -----> MgO + CO2 ---- u are getting one mole ov a gas which means its 24dm3
C- 2Mg(NO3)2 ------> 2MgO + 4NO2 + O2 ---- here its 5 moles of gas

Q20 -try out the structures....thats the only option
if u dont get it tell me

Q3-- its easy
write the equation first
C6H12 + 9O2 ------> 6CO2 + 6H2O
find the mass of CO2 nd H2O
6CO2 = 108
6H20 = 264
108/264 = .41