Chemistry: Post your doubts here!

[nightrider1993]

Hey guys, why don't we post all yearly P1 MCQ's preparation thread for chemistry with solved explanations just as there is for physics?

http://www.xtremepapers.com/community/threads/p1-mcqs-preparation-thread-for-chemistry-only.19324/

 

[Amy Bloom]

smzimran
I need your help. can you clear that doubt in me please?
Can you explain the relationship between nuclear charge, effective nuclear charge and shielding effect? Is the nuclear charge concerned with the overall charge of an element/ion???

 

[smzimran]

smzimran
I need your help. can you clear that doubt in me please?
Can you explain the relationship between nuclear charge, effective nuclear charge and shielding effect? Is the nuclear charge concerned with the overall charge of an element/ion???

I believe i have explained this to you before.
ANyways:
Nuclear charge is the charge of ALL protons in the nucleus.
For example, for a nucleus of carbon (which has 6 protons in its nucleus), the nuclear charge is +6

Effective nuclear charge is the net charge on an ion.
In an atom, the charge of protons and charge of electrons cancel each other out as there are equla number of protons and electrons.
In an ion , however, the protons are not equal to electrons so a net charge is developed. This is effective nuclear charge.

Shielding effect is the weakening of electrostatic force of attraction of the nucleus to valence shell electrons by the nearer shell electrons.
It results in the atom losing electrons mostly...

 

[Amy Bloom]

I believe i have explained this to you before.
ANyways:
Nuclear charge is the charge of ALL protons in the nucleus.
For example, for a nucleus of carbon (which has 6 protons in its nucleus), the nuclear charge is +6

Effective nuclear charge is the net charge on an ion.
In an atom, the charge of protons and charge of electrons cancel each other out as there are equla number of protons and electrons.
In an ion , however, the protons are not equal to electrons so a net charge is developed. This is effective nuclear charge.

Shielding effect is the weakening of electrostatic force of attraction of the nucleus to valence shell electrons by the nearer shell electrons.
It results in the atom losing electrons mostly...

Yeah its just that i felt confused again. But now i'm more confident. Thanks mate.

 

[Soldier313]

Assalamon alaykum wrwb

can someone pls pls urgently help me with qn no 1aii.) i am kinda confused, why does the LHS have to be negative electrode, and if possible could a diagram be drawn?

QP: http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s05_qp_4.pdf

MS: http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_s05_ms_4.pdf

Jazakallah!

 

[nightrider1993]

Assalamon alaykum wrwb

can someone pls pls urgently help me with qn no 1aii.) i am kinda confused, why does the LHS have to be negative electrode, and if possible could a diagram be drawn?

QP: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_4.pdf

MS: http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_ms_4.pdf

Jazakallah!

2(H+) + 2(e) = (H2)
A negative electrode(cathode) is a source of electrons. Therefore since hydrogen gas is produced, so left electrode is connected to the negative power source. Hope this answers it.

 

[Soldier313]

2(H+) + 2(e) = (H2)
A negative electrode(cathode) is a source of electrons. Therefore since hydrogen gas is produced, so left electrode is connected to the negative power source. Hope this answers it.

thanx a lot bro, but as you said -ve electrode is a source of electrons, the LHS is accepting electrons rather than donating, so how does it become -ve electrode??
hope my question is understand-able.....

 

[nightrider1993]

thanx a lot bro, but as you said -ve electrode is a source of electrons, the LHS is accepting electrons rather than donating, so how does it become -ve electrode??
hope my question is understand-able.....

The electrode is not accepting the electrons, hydrogen is accepting it. And the electrode is donating the electrons to the hydrogen ions. Hope it clarifies it.. if not say it

 

[Soldier313]

The electrode is not accepting the electrons, hydrogen is accepting it. And the electrode is donating the electrons to the hydrogen ions. Hope it clarifies it.. if not say it

hmmm, it's starting to make sense thanx a lot

 

[nightrider1993]

hmmm, it's starting to make sense thanx a lot

If you still have any doubts say it... i'll try to clarify it otherwise someone else might need to help

 

[Soldier313]

If you still have any doubts say it... i'll try to clarify it otherwise someone else might need to help

thanx you have made it absolutely clear

 

[nightrider1993]

thanx you have made it absolutely clear

No problem. Glad to help

 

[nightrider1993]

Describe and explain how the solubility of sulfates of group 2 elements vary down the group.
Is there a easy way of memorizing how the enthalpy of hydration, lattice enthalpy and enthalpy of solution change down the group?

 

[nightrider1993]

And is there a easy way for memorizing the positive and negative sign of a endo/exothermic reaction? i always get confused b/w the 2

 

[Amy Bloom]

And is there a easy way for memorizing the positive and negative sign of a endo/exothermic reaction? i always get confused b/w the 2

Take it upon yourself like taking chocolates.
"Endo" is a latin word which means to absorb/ to take in/ to accept... you accept chocolates so, its a positive thing. So an endothermic reaction is +ve kJmol-1
"Exo" is yet another latin word which means to release/to give out... so you don't like when chocolates go away from you, so you have a negative feeling. Exothermic reactions are -ve kJmol-1
Hope it helped.

 

[nightrider1993]

Take it upon yourself like taking chocolates.
"Endo" is a latin word which means to absorb/ to take in/ to accept... you accept chocolates so, its a positive thing. So an endothermic reaction is +ve kJmol-1
"Exo" is yet another latin word which means to release/to give out... so you don't like when chocolates go away from you, so you have a negative feeling. Exothermic reactions are -ve kJmol-1
Hope it helped.

Thanks alot Amy Bloom.... talking abt chocolate helped alot as well, bcoz i love chocolates...

 

[Amy Bloom]

Thanks alot Amy Bloom.... talking abt chocolate helped alot as well, bcoz i love chocolates...

Its okay! So, if u have to remember something in chemistry always relate it to something that you like.

 

[Amy Bloom]

Hello there can any1 clear my doubt over:

 

[JulyMei]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_5.pdf

can anybody help???
question 2(e)

what line should I draw? and how to calculate the faraday?

 

[bamteck]

Please someone help me chemistry P53 June 2012 for no. 1 (c) & (e)

https://docs.google.com/viewer?a=v&...qQm-6a&sig=AHIEtbS4YwHRNENYSo0M_FrPwShhfNSZaQ