[orgoclear]

Which of the following is most hydrated?
(a) H+   (b) Li+   (c) Be(2+)    (d) Al3+

I know that amount of hydration depends on charge density. But here I am unable to compare with that

[orgoclear]

anyone?

[Ranadeep]

Be⁺² because its the smallest i guess

[orgoclear]

hydration enthalpies say something else

http://www.science.uwaterloo.ca/~cchieh/cact/applychem/hydration.html

it says Al3+ has highest enthalpy .. any plausible reasons?

[orgoclear]

can anyone explain the values obtained ?

[savy2020]

Be and Al are diagonal elements. So they've nearly similar Electronegativities and atomic/ionic radii.
So in comparing the heats of hydration of Be2+ and Al3+, Al3+ has higher enthalpy of hydration due to higher charge density on it.

[Schrödinger]

Please think on the following lines:

Hydration enthalpy depends mainly upon :
1.size of the ion
2.charge on the atom

Please try to figure out how 1 and 2 are related to hydration enthalpy - it's quite simple, plain logic.

I'd be glad to help once you reply.

[orgoclear]

thanks savy.. the diagonal relationship escaped my mind.. (best of luck for incho)

@schrodinger: we three (savy, me and u) are a bunch of iit preparing students so you can expect me to know what hydration enthalpy depends upon.. Look at the initial question

I know that amount of hydration depends on charge density. But here I am unable to compare with that

[Schrödinger]

i'm sorry orgo... didn't read that bit   

[diptarka]

actually hydration energy is directly proportional to charge squared and inversely to radius. Thus effect of charge is much more important making Al3+ the answer