Ek 1001 gc #805

[TotalDomination]

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Which of the following cations is the strongest acid in aqueous solution?

Fe+3, Ca+2, Cu+2, or Zn+2.

Answer is Fe+3 because it is the smallest size and has the greatest charge.

Greatest charge part I can understand....because it wants electrons more (def. of a lewis acid). But...how is Fe+3 the smallest ion? I'm looking at Cu+2 and thinking it might be smaller because it has more protons and is also to the right of Fe. Can anyone provide some insight??? Thanks a bunch, first post and all that shizz.

 

[sdm33]

less electrons is smaller Fe +3 is smaller because it has less electrons, also zeff gets bigger going left to right. Zeff = valence electrons
it is easier if they ask Mg and Mg+2 , Mg+2 is smaller.
only if they were isoelectronic series then I would look at the largest atomic number to be the smallest atom

 

[TotalDomination]

Thanks....that still makes zero sense to me. Maybe I need to sleep and look at it again tomorrow....any alternative explanations would be appreciated as well. Having a dumb day.

Additionally, how high do people generally score on EK1001 q's? I'm on my first go around. I haven't reviewed the material in 6 months...briefly looked at the end of kaplan chapters. I'm scoring consistently about ~70% on all sections in gen chem. I feel extremely stupid, but I figure I would rather make mistakes now and learn from them asap. Still, kind of messing with my head that i'm getting so many concepts wrong.

Advice? Comments? Do I just need to chill out?