Gchem question

[lor]

Gurus,
Some Gchem question for you:
what is the molecular formula if a compound contains 40.9%C, 4.58%H and 54.52%O, molecular weight is 264

what is the quickest way to solve this problem by looking at the ansswer choices
C9H12O9
C3H4O3

Question: which one has the greatest atomic radius and why did you pick that?
Ca+2 F- Ar O-2 He

which one has the greatest ionization energy and why did you pick that one
K K+ Na Na+ Ca

Thanks for your help!

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[skyisblue]

quickest way? add them up

 

[joonkimdds]

Gurus,
Some Gchem question for you:
what is the molecular formula if a compound contains 40.9%C, 4.58%H and 54.52%O, molecular weight is 264

what is the quickest way to solve this problem by looking at the ansswer choices
C9H12O9
C3H4O3

Question: which one has the greatest atomic radius and why did you pick that?
Ca+2 F- Ar O-2 He

which one has the greatest ionization energy and why did you pick that one
K K+ Na Na+ Ca

Thanks for your help!

are there 4 different questions in this thread? or is it 3?
if first and second questions are 1 problem instead of 2 problems, then
your answer choices of the 2nd part of the first problem is wrong.
Anyway, my answer for the first problem is C9 H1 O12.

my answer for the 2nd or the third or whatever is Ca+2.
I think Ca+2 is basically same as Ar so I hope someone could clarify this for me.

my answer for the last is Na+
ionization energy = how hard it is to remove electron from nucleus.
Na + is octet(Ne) so it is in stable form and it definitely doesn't want to be unstable on purpose, understand?
K+ is also octet(Ar) but it is furthur away from the nucleus compared to Ne thus it is easier to remove.

If any of my answers are wrong, or if you have more questions, please PM me, since I usually don't read the same thread twice.
I will gladly answer your questions, so feel free to ask questions. I check my email 24hours/7days and it's [email protected]. so send me email too if u wish.

 

[doc toothache]

Quickest way: there are 18 atoms (C9 O9)with ave. mol. wgt. of 14;
14x18=?; or 6 atoms (C3 O3) with ave. mol. wgt. of 14; 6x14=?
Which is larger and closer to 264?

Atomic radius- Based on mol. wgt the top 3 need to be Ca+2, F-; and Ar. Positive ions tend to be smaller than parent ion as they lose electrons. Negative ions are bigger than the atoms they come from. In this case, it is, at best, a lucky guess since the values for Ca+2 is 114pm, F- is 119pm and Ar is 98pm.

The ionization energy to remove the 1st electron (1st ionization) is lower than the energy to remove the second electron. Therefore, eliminate Na, K, and Ca. The ionization energy increase going up the periodic table. Na+ (2nd ionization energy 4,562 kj/mole) is chosen over K+ (2nd ionization energy 3,051 kj/mole).

 

[joonkimdds]

Atomic radius- Based on mol. wgt the top 3 need to be Ca+2, F-; and Ar. Positive ions tend to be smaller than parent ion as they lose electrons. Negative ions are bigger than the atoms they come from. In this case, it is, at best, a lucky guess since the values for Ca+2 is 114pm, F- is 119pm and Ar is 98pm.

aren't Ca+2 and Ar the same?

 

[doc toothache]

The same? How?

Ca atomic radius 197pm
Ca+2 114pm
Ar 98 pm

www.chemicool.com/elements/argon

 

[joonkimdds]

The same? How?

Ca atomic radius 197pm
Ca+2 114pm
Ar 98 pm

www.chemicool.com/elements/argon

hm...because they got the exact same amount of electrons

 

[doc toothache]

hm... I see.

Argon has 18 protons tugging on 18 electrons.
Ca+2 has 20 protons tugging on 18 electrons! Apparently the 2 extra protons have more influence on the atomic radius than the loss of the 2 electrons.

 

[joonkimdds]

hm... I see.

Argon has 18 protons tugging on 18 electrons.
Ca+2 has 20 protons tugging on 18 electrons! Apparently the 2 extra protons have more influence on the atomic radius than the loss of the 2 electrons.

then shouldn't Ca+2 have smaller radius since it has more protons than Ar and so Ca+2 attracts the same amount of electrons more than Ar would attract.

 

[doc toothache]

then shouldn't Ca+2 have smaller radius since it has more protons than Ar and so Ca+2 attracts the same amount of electrons more than Ar would attract.

Maybe Ca+2 should have a smaller radius, but based on the information supplied, it apparently does not.