Chemistry: Post your doubts here!

[CaptainDanger]

*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?

 

[Sabcore]

Hey guys, I need that explained. I don't have an idea how to do this whole question. Someone please explain to me in clear details if possible on how to solve this question. I need this by tomorrow.

Thanks.

 

[Dayyanah]

I need help with mass spectrometer in applications... how do u draw the peaks n how are their heights calculated?

 

[smzimran]

Hey guys, I need that explained. I don't have an idea how to do this whole question. Someone please explain to me in clear details if possible on how to solve this question. I need this by tomorrow.

Thanks.

(a) You may use the method in which you put your reacting flask on an electronic balance and measure the rate of decrease of mass as brown N2 gas escapes, i am not giving the details of this procedure, i hope you know it.

(b) check the initial rates
It is 7 when 0.01 mol/dm3 is used and
it is 3.5 when 0.005 mol/dm3 is used
We can see that as concentration increases by 2, the rate is also doubled
Therefore, the order of reaction is 1

(c) Increasing temp should increase rate as a higher temp means that reacting particles will have greater energy and so, more effective collisions take place which increases rate of production of products...

 

[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!!