Chemistry: Post your doubts here!

[smzimran]

*Which one these always applies to a nucleophile?

A) It attacks a double bond.
B) It has a lone pair of electrons.
C) It has a single atom.
D) It is negatively charged.

Why its not D?

It is not D because there are some nucleophiles which are not negatively charged, for example:
NH3 (ammonia) is a nucleophile as it has lone pair of electrons but it is not negatively charged...

 

[Muhammad Bin Anis]

It is not D because there are some nucleophiles which are not negatively charged, for example:
NH3 (ammonia) is a nucleophile as it has lone pair of electrons but it is not negatively charged...

yeah the same goes for water H2O
H2O is a nucleophile because it has a LONE PAIR OF ELECTRONS.

every nucleophile must have a lone pair!

 

[Muhammad Bin Anis]

Have a look At the question and explain it to me

Please someone explain it
marking scheme says D
and i chose"B"

 

[Muhammad Bin Anis]

Heres another one
Q10
Examiner report says "A"
Can u explain it to me?

 

[Muhammad Bin Anis]

Here one more:
Marking scheme says "c" and i chose "D"

 

[Muhammad Bin Anis]

Can anyone explain these to me (Both of them are from p1 , sec3
Amswers are :
38 : B ( 1 and 2 are corrct)
39 : C (2 and 3 are correct)

 

[samwickz]

Here one more:
Marking scheme says "c" and i chose "D"

View attachment 5823

im not sure but i think its C tooooooo cuz u c when algae grow it covers up the water surface lyk floating on it and stuff so then as a result the plants underwater dont get sunlight so no photosynthesis can happen etc etc So eventually d plants die this causes bacteria to grow again by feeding on the dead plants. now this can cause marine animals to die due to lack f oxygen well ya thats wat i think then again i myt b wrong

 

[Muhammad Bin Anis]

im not sure but i think its C tooooooo cuz u c when algae grow it covers up the water surface lyk floating on it and stuff so then as a result the plants underwater dont get sunlight so no photosynthesis can happen etc etc So eventually d plants die this causes bacteria to grow again by feeding on the dead plants. now this can cause marine animals to die due to lack f oxygen well ya thats wat i think then again i myt b wrong

fine got it : thankieee

 

[Dayyanah]

Heres another one
Q1
Examiner report says "A"
Can u explain it to me?
View attachment 5822

I think it shud b A bcz carbon is found in different allotropes such as diamond and graphite so it needs to be converted to a single atom first. Hydrogen is found as a diatomic molecule and that too needs to b atomised then comes the enthalpy of formation.
Im not 100% sure but i think thats how it it

 

[DragonCub]

Have a look At the question and explain it to me

Please someone explain it
marking scheme says D
and i chose"B"

H2O in the reactants does not count as solute molecule. So the reaction actually increases the mole number of solute molecule. nRT is now bigger, so Π ought to increase.

 

[Muhammad Bin Anis]

H2O in the reactants does not count as solute molecule. So the reaction actually increases the mole number of solute molecule. nRT is now bigger, so Π ought to increase.

Dont you think the nummber of moles decreases because as the reaction proceeds the amount of reactant decreases and the amount of product increases???

 

[Muhammad Bin Anis]

Another one
someone please explain!

 

[smzimran]

View attachment 5876 Another one
someone please explain!

Should be D

 

[USMAN Sheikh]

Quickly need help !!!! how to do molar calcu lation in 1st question of titration the value of titre is 43.75 !!! need help with full details !!

 

[xhizors]

May/June 2011 Q7, Q10, Q12
http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s11_qp_12.pdf

plz help

 

[USMAN Sheikh]

In question no 7 use hess law !! the equation build by using hess law will be -940+X=2*(-110) it will be C +720!!

 

[USMAN Sheikh]

in quesstion 12 ans should be B in it u have to use common sense as accross the group EN inc and Down the group it decreases !! so Be will be the answer asfrom Be to Al we are moving one step in fovour to inc EN and one step down in order to dec EN hence both will cancel each other !

 

[USMAN Sheikh]

In ques 17 find out epirical formula using percentage it will be values of empirical will be 1:1.5:1.5:10:7
in above eq Ca is 2 so we can do it by ratio method if ca is 1---------- 1.5 of AL so if Cais 2 ---------X
ie al=X=3 si will also be three similar rations C is your ans

 

[USMAN Sheikh]

Quickly need help !!!! how to do molar calcu lation in 1st question of titration the value of titre is 43.75 !!! need help with full details !!

 

[xhizors]

In question no 7 use hess law !! the equation build by using hess law will be -940+X=2*(-110) it will be C +720!!

Thanks i forgot the fact of 2 mol


Thanks for other two answers aswell