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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: Haaks18 on November 27, 2010, 12:15:17 am

Title: Any Chem AS question to be posted here :):)
Post by: Haaks18 on November 27, 2010, 12:15:17 am
all the questions right here will be mainly about Chem AS.. Here u can discuss and the questions u r confused about and OFCOURSE nothing is possible in SF ;)
Title: Re: Any Chem AS question to be posted here :):)
Post by: Haaks18 on November 27, 2010, 12:18:04 am
What does Shielding in the Atomic Structure chapter means??
And in Atomic Structure do we have to knw about Nuclear fission and fusion?!
Thanks aloot :)
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 27, 2010, 08:15:01 am
Quote from: Haaks18 on November 27, 2010, 12:15:17 am
all the questions right here will be mainly about Chem AS.. Here u can discuss and the questions u r confused about and OFCOURSE nothing is possible in SF ;)

You mean impossible, buddy.  ;)

Sheilding Effect of Electrons in an atom.
All electrons are negetively charged and repel each other. Electrons in filled inner shells repel electrons in the outer shells and reduce the effect of positive nuclear charge. This is called Shielding effect. The greater the shielding effect upon an electron, the lower is the Ionization energy.

(These come under the heading of Nuclear Chemistry)
Nuclear Fission is when a nucleus splits into half and produces a great amount of energy. The energy generated by splitting the atom was called atomic energy.

Nuclear Fusion is when  two small nuclei such as those in Hydrogen combine to form a large nucleus. The energy is released in tremendous amount.

Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 27, 2010, 08:19:56 am
You can post your doubts, here

https://studentforums.biz/sciences-149/chemistry-doubts-10366/
or here
https://studentforums.biz/sciences-149/edexcel-chemistry-doubts
(depending on what you take)

P.S - Good luck!
Title: Re: Any Chem AS question to be posted here :):)
Post by: AS-Girl on November 27, 2010, 11:19:36 am
hey again
i have a question that came to my mind yesterday..
we did solubiltiy product for compounds which have the same mole ratio like   AgCl---->Ag +   and Cl-

but what if the compound has a different miole ration like Mg(OH)2-------->Mg2+ and 2OH-

how can we get the solubility of both ions??

i know we get Ksp= [Mg2+] [Oh-]2

then what??
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 27, 2010, 02:40:08 pm
For eg:- The Solubility Product of Mg(OH)2 is 1.00x10-12                        

                    Mg(OH)2----->Mg2++2OH-


Ratio =                          1                  :          1              :       2

(2+1 = 3)
 Ksp = [Mg2+]3
find the cuberoot of 1.00x10-12 = 1x10-4 (this answer will be for Mg2+ since its ratio is 1)
For OH- = 2x1x10-4 = 2x10-4
Since it is 2OH-, we do 2x10-4 = 4x10-8
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 27, 2010, 02:48:33 pm
I'll give another example with the same numbers.

The solubility product of Siver Chromate (Ag2CrO4)at 25degree celcius is 1.00x10-12.
Calculate the solubility of silver chromate in moldm-3 at this temperature.

           Ag2CrO4----->2Ag2++CrO42-
Ratio = 1:2:1

Ksp = [Ag2+]3
cube root of 1.00x10-12 = 1x10-4 for chromate.
2x1x10-4 = 2 x10-4 for Ag2+ multiply this by 2
Title: Re: Any Chem AS question to be posted here :):)
Post by: AS-Girl on November 27, 2010, 08:24:55 pm
Another question...i know i made all of u teird from my questions!!

25. If the solubility product (Ksp) for lead oxalate (PbC2O4) is equal to 8.5 x 10-9,
what is the molar solubility of a saturated solution of lead oxalate?

(a) 8.5 x 10+9 mole / liter (c) 9.2 x 10-5 mole / liter
(b) 9.2 x 10+5 mole / liter (d) 8.5 x 10-9 mole / liter

??:S :S
Title: Re: Any Chem AS question to be posted here :):)
Post by: Haaks18 on November 28, 2010, 04:22:52 am
Is This Chemistry AS edexcel :/
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 28, 2010, 04:48:56 am
Quote from: AS-Girl on November 27, 2010, 08:24:55 pm
Another question...i know i made all of u teird from my questions!!

25. If the solubility product (Ksp) for lead oxalate (PbC2O4) is equal to 8.5 x 10-9,
what is the molar solubility of a saturated solution of lead oxalate?

(a) 8.5 x 10+9 mole / liter (c) 9.2 x 10-5 mole / liter
(b) 9.2 x 10+5 mole / liter (d) 8.5 x 10-9 mole / liter

??:S :S

You have asked this question before(And Deadly_King had already solved it.). The only difference is that the question is the other way round. ;)
https://studentforums.biz/sciences-149/chemistry-people-come-in!!/

@Haaks - I dont know, but I've answered your questions above. :P
Title: Re: Any Chem AS question to be posted here :):)
Post by: Haaks18 on November 29, 2010, 10:32:25 pm
Thanks for answering :p
Title: Re: Any Chem AS question to be posted here :):)
Post by: Deadly_king on November 30, 2010, 05:04:55 am
Quote from: Haaks18 on November 28, 2010, 04:22:52 am
Is This Chemistry AS edexcel :/

Nope that is A2. ;)

Good job daughter. ;D
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on November 30, 2010, 05:19:05 am
Quote from: Martin Luther King Jr on November 30, 2010, 05:04:55 am
Nope that is A2. ;)

Good job daughter. ;D

You just made me smile. ;D :D
Title: Re: Any Chem AS question to be posted here :):)
Post by: AS-Girl on December 09, 2010, 06:54:48 pm
here are 2 questions :

1) If the pH of a tomato juice is 4.50, then the hydroxide ion concentartion [OH]- of the juice is:
a) 3.16X 10^(-5) mole/litre
b)1.00X 10^(-14) mole/litre
c) 3.16X10^(-9) mole/litre
d) 1.00X 10^(-7) mole/litre


2)How many ions per formula unit would you find if you dissolve (NH4)2[Ce(NO3)6] in water?
a) 3
b)9
c) 2
d) 6


Thanks in advance :)

Title: Re: Any Chem AS question to be posted here :):)
Post by: tmisterr on December 10, 2010, 06:51:03 am
Quote from: AS-Girl on December 09, 2010, 06:54:48 pm
here are 2 questions :

1) If the pH of a tomato juice is 4.50, then the hydroxide ion concentartion [OH]- of the juice is:
a) 3.16X 10^(-5) mole/litre
b)1.00X 10^(-14) mole/litre
c) 3.16X10^(-9) mole/litre
d) 1.00X 10^(-7) mole/litre


2)How many ions per formula unit would you find if you dissolve (NH4)2[Ce(NO3)6] in water?
a) 3
b)9
c) 2
d) 6


Thanks in advance :)



1. hmm, i'm getting an answer not included in the choices......Since pH is -log[H+], we need to un-log the pH value to find the hydrogen ion concentration. which is 10-4.5= 3.16x10-5. since the tomato juice is in aqueous form and we know the ionic product of water (assuming it is at rtp its value is 1x10-14), we can use it to find the hydroxide ion concentration. Kw=[H+]*[OH-] so [OH-]=Kw/[H+] which is 1x10-14/3.16x10-5=3.16x10-10

2. it will dissolve into 2NH4+ and the complex ion [Ce(NO3)6]2- where NO3 is the ligand, assuming that it completely dissociates. so 2 ammonium ions and one complex ion to give a total of 3 ions per unit formula so a is your answer
Title: Re: Any Chem AS question to be posted here :):)
Post by: AS-Girl on December 10, 2010, 10:38:33 am
thanks tmisterr! :)
The answer for the first question is C..but it's not exactly the same answer i got..so u r probably right ;)


I did it in an easier way
this was my way
p[H+] + p[OH-]=14
4.5 + x= 14
x=9.5

so i replaced all the values given in the equation -log[oh] =9.5
C was the only one close to 9.5..so predicted it was the answer!

Title: Re: Any Chem AS question to be posted here :):)
Post by: Haaks18 on December 10, 2010, 02:29:13 pm
There is a question which says Na,Na+,Mg,Mg+2,Cl,Cl- Arrange in order of the largest radius first and the smallest last

Another question says :D:D Arrange in order of polarising power..strongest first..Na+,Mg+2,Al+3 & K

Last Question  ::) ::) Arrange in order of the strongest bond first.. C-Cl, C-C and C-Br

Tada :D
Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on December 10, 2010, 04:02:52 pm
Quote from: Haaks18 on December 10, 2010, 02:29:13 pm
There is a question which says Na,Na+,Mg,Mg+2,Cl,Cl- Arrange in order of the largest radius first and the smallest last
Another question says :D:D Arrange in order of polarising power..strongest first..Na+,Mg+2,Al+3 & K
Last Question  ::) ::) Arrange in order of the strongest bond first.. C-Cl, C-C and C-Br
Tada :D

1) Cl-, Cl, Mg2+, Na+, Mg, Na.
cations are smaller in size then there metal atoms, and anions are larger then their nonmetal atoms.

2) smaller size and greater charge creates high charge density and has the most polarizing power.
    Al3+, Mg2+, Na+, K+

3) C-C, C-Cl, C-Br.
Title: Re: Any Chem AS question to be posted here :):)
Post by: tmisterr on December 11, 2010, 05:30:03 pm
Quote from: Hamlet on December 10, 2010, 04:02:52 pm
1) Cl-, Cl, Mg2+, Na+, Mg, Na.
cations are smaller in size then there metal atoms, and anions are larger then their nonmetal atoms.

2) smaller size and greater charge creates high charge density and has the most polarizing power.
    Al3+, Mg2+, Na+, K+

3) C-C, C-Cl, C-Br.


For 1 I disagree, I think it should be:
Na, Cl-, Mg, Cl, Na+, Mg2+

Since the are all in the same period they have the same number of energy levels, but as you move along the period, the nuclear charge increases so size of ATOMS get smaller, hence Na is the largest atom, then Mg then Cl. When it comes to ions, since Na+ and Mg2+ are bother losing an energy level so they only have 2 shells now. they will be the smallest, however Mg2+ has a higher nuclear charge so it will be smaller than Na+. for Cl-, it still has 3 energy levels since it has gained an electron to the third energy level. since nuclear charge is the same as Cl, it will be larger that a Cl atom, and even Mg atom, but smaller than Na+ since Na has a much smaller nuclear charge than Cl-

Title: Re: Any Chem AS question to be posted here :):)
Post by: Amelia on December 11, 2010, 06:46:12 pm
Quote from: tmisterr on December 11, 2010, 05:30:03 pm
For 1 I disagree, I think it should be:
Na, Cl-, Mg, Cl, Na+, Mg2+

Since the are all in the same period they have the same number of energy levels, but as you move along the period, the nuclear charge increases so size of ATOMS get smaller, hence Na is the largest atom, then Mg then Cl. When it comes to ions, since Na+ and Mg2+ are bother losing an energy level so they only have 2 shells now. they will be the smallest, however Mg2+ has a higher nuclear charge so it will be smaller than Na+. for Cl-, it still has 3 energy levels since it has gained an electron to the third energy level. since nuclear charge is the same as Cl, it will be larger that a Cl atom, and even Mg atom, but smaller than Na+ since Na has a much smaller nuclear charge than Cl-

You are right. It said largest radius first, I misread the question.
 Thanks for the correction. ;)
Title: Re: Any Chem AS question to be posted here :):)
Post by: Haaks18 on December 13, 2010, 10:03:11 am
Thaaanks you but isnt it Na and then Mg and then Cl- and then Cl and then Na+ and at last Mg+2?!
Title: Re: Any Chem AS question to be posted here :):)
Post by: Deadly_king on December 13, 2010, 10:57:59 am
Quote from: Haaks18 on December 13, 2010, 10:03:11 am
Thaaanks you but isnt it Na and then Mg and then Cl- and then Cl and then Na+ and at last Mg+2?!

The answer is as follows:

Na, Cl-, Mg, Cl, Na+, Mg2+

NOTE :
1. Leaving the noble gases out, atoms get smaller as you go across a period.

2. The ionic radii fall as you go across the period though we need to look at the positive and negative ions separately.

3. You're provided the exact length for the radii of these elements in the data booklet.

Click here (http://www.chemguide.co.uk/atoms/properties/atradius.html) for more notes about it.