Question on Gchem

[YoonS]

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My test date is approaching and I am reall really nervous.

Score isn't improving much

I came up with some questions while I was taking Gchem section test.



1. What is the best explanation for why Ca2+ has a larger atomic radius than Ar?

A. The Ca cation has less electrons
B. The Ca cation is not a noble gas
C. The Ca cation has more electrons
D. The Ca cation has less protons
E. The Ca cation has more protons


I put E as my answer but it was D. What am i missing??

And here is one more question


2. If enough water is added to 11g of CaCl2 to make 100ml of solution, what is the molarity of the solution

A. 9M
B. 10M
C. 11M
D. 12M
E. None of the above


Thank you so much!

 

[qkchen]

My test date is approaching and I am reall really nervous.

Score isn't improving much

I came up with some questions while I was taking Gchem section test.



1. What is the best explanation for why Ca2+ has a larger atomic radius than Ar?

A. The Ca cation has less electrons
B. The Ca cation is not a noble gas
C. The Ca cation has more electrons
D. The Ca cation has less protons
E. The Ca cation has more protons


I put E as my answer but it was D. What am i missing??

And here is one more question


2. If enough water is added to 11g of CaCl2 to make 100ml of solution, what is the molarity of the solution

A. 9M
B. 10M
C. 11M
D. 12M
E. None of the above


Thank you so much!

for the first question, i thought Ca2+ would have a smaller ionic radius compared to Ar (because Ca has more protons than Ar).

for the second question, i got 1M as my answer.

 

[sacapuntas]

11g of CaCL2 and 100 ml of solution
CaCL2 = 40.078 + 35.453*2 gm/mole or 110.984 grams per mole
11g/110.984 grams per mole = about .1 mole
Molarity = moles/liters so .1 moles/.1 L = 1M so none of the above

 

[sacapuntas]

And for your first question, I think you are right, the Ca cation has more protons and that is why it is bigger...I think it must be a typo in the answer key.

 

[RCLEE]

I agree with you guys that Ca2+ has a smaller atomic radius. It has a higher effective nuclear charge than Ar.

1M [] for the second.

Yoons, what's the source of these test questions?

 

[dantemac]

1. What is the best explanation for why Ca2+ has a larger atomic radius than Ar?

A. The Ca cation has less electrons
B. The Ca cation is not a noble gas
C. The Ca cation has more electrons
D. The Ca cation has less protons
E. The Ca cation has more protons


I think less protons would hold the electrons less tightly to the nucleus. That way, the electron "orbits" are larger in radius. Perhaps D is correct? Not sure...

 

[sacapuntas]

I guess I am confused why D could be correct...Ca has more protons than Ar so how can D be correct?

A is not correct - they have the same electrons.
B doesn't matter for size
C - Ca does not have more electrons
D - Ca does not have less protons
E - Ca having more protons is the only answer that makes sense. I think it must be a typ.

1. What is the best explanation for why Ca2+ has a larger atomic radius than Ar?

A. The Ca cation has less electrons
B. The Ca cation is not a noble gas
C. The Ca cation has more electrons
D. The Ca cation has less protons
E. The Ca cation has more protons


I think less protons would hold the electrons less tightly to the nucleus. That way, the electron "orbits" are larger in radius. Perhaps D is correct? Not sure...

 

[2th Doc]

D cannot be correct because if the Ca2+ ion has less protons then Ar, then it cannot be a Ca2+ ion. An element is defined by the number of protons in its nucleus. The Ca2+ ion will not have less protons than Ar or a neutral Ca atom for that matter... so answer D makes no sense by that logic.

 

[dantemac]

Ca2+ has lost two electrons so it has the same number of electrons as Argon. But remember the trend for atomic radius: down and to the left.