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Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: ashwinkandel on October 04, 2010, 01:35:39 pm

Title: chemistry MCQ
Post by: ashwinkandel on October 04, 2010, 01:35:39 pm
i have attached question of chemistry. i am confused with question number 2. how do we determine the proton, neutron and electrons of the compounds given in option B, C and D respectively.
Title: Re: chemistry MCQ
Post by: ashwinkandel on October 04, 2010, 02:36:41 pm
one more question . i m having problem with question no. 5 in the following attachment. can someone reply me with the solution and reasoning. i am having my chemistry internal exams tomorrow so plz reply me quickly.
Title: Re: chemistry MCQ
Post by: nid404 on October 04, 2010, 03:01:57 pm
i have attached question of chemistry. i am confused with question number 2. how do we determine the proton, neutron and electrons of the compounds given in option B, C and D respectively.

B- H3O+

here's the structure.

(http://image.wistatutor.com/content/chemical-bonding/hydronium-ion.jpeg)

There are 8 electrons + 2 in the first orbit of O.  = 10 electrons. Neutrons= 8(no neutrons in H) in O Protons=8  and 1 each H= 11

C- OD-

So O2- and D+ --> OD-

10 electrons, 9 neutrons(Deuterium has 1 neutron) and 9 protons(8 of O and 1 of D)

D- OH-


So O2- + H+--> OH-

10 electrons, 8 neutrons(no neutrons in H) and 9 protons( 8 in O and 1 in H)

Questions asks which one has more electrons than protons. So B is ruled out.

Now which one of C and D have more protons than neutrons. It's D. Hence D :P


Title: Re: chemistry MCQ
Post by: nid404 on October 04, 2010, 03:22:09 pm
one more question . i m having problem with question no. 5 in the following attachment. can someone reply me with the solution and reasoning. i am having my chemistry internal exams tomorrow so plz reply me quickly.

8 electrons.

Electronics config.

1s22s22p4

A is not the right configuration because electrons do not couple when there's an empty pz orbital.
B is the right one, the electrons fill up individually first in px, py and pz and then start coupling after each of them has at least 1 electron.
C and D are hybridized states..high energy.

So B
Title: Re: chemistry MCQ
Post by: nid404 on October 04, 2010, 03:25:15 pm
Was going to post...
anyways, got your 1st answer!!

Ms. Garfieldo. :P

The orbit nearest to the nucleus has the most energy!

So the electrons will start filling in different orbitals.

See the 2px orbital, the left of the three orbitals, it has got only one electron, and hence, others have two in them.

so this atom will be in it's lowest energy state compared to the others.

I tried, hope i was not wrong and u understood!!  8)

What according to you is the answer to this question?  ::)
Title: Re: chemistry MCQ
Post by: Deadly_king on October 04, 2010, 03:38:15 pm
8 electrons.

Electronics config.

1s22s22p4

A is not the right configuration because electrons do not couple when there's an empty pz orbital.
B is the right one, the electrons fill up individually first in px, py and pz and then start coupling after each of them has at least 1 electron.
C and D are hybridized states..high energy.

So B

Wow.........nice explanation :)

+ rep though I must spread the love first  ;)
Title: Re: chemistry MCQ
Post by: ashwinkandel on October 04, 2010, 03:49:25 pm
thank you Garfield very much. simple and great explanation .i understood it very nicely. thanks. and +rep too
Title: Re: chemistry MCQ
Post by: Arthur Bon Zavi on October 04, 2010, 04:23:31 pm
What according to you is the answer to this question?  ::)

was B i didn't see the arrangement of B prop.. sorry!!

Though I deleted my post! Forgive.  :P
Title: Re: chemistry MCQ
Post by: nid404 on October 04, 2010, 04:46:59 pm
You're welcome =)

@theonlyone- lol...no problem  ;)
Title: Re: chemistry MCQ
Post by: Arthur Bon Zavi on October 04, 2010, 04:56:17 pm
You're welcome =)

@theonlyone- lol...no problem  ;)

 :-* :-* Thank You..!