Why is #"H"_2# not very soluble in water?

2 Answers
David Drayer
Oct 27, 2017

dihydrogen or Hydrogen gas is a non polar molecule. Water is highly polar, non polar and polar do not mix.

Explanation:

dihydrogen of # H_2# is a purely polar molecule as both atoms have the same electro negativity of 2.2.
Hydrogen oxide water # H_2O# is a highly polar molecule with a difference of 1.3- 1.4 in electro negativity. ( 3.5 -2.2)

Non polar molecules are not soluble in polar molecules.

Truong-Son N.
Oct 27, 2017

Because its intermolecular forces are drastically weaker than those in water.

#bb("H"_2)#, a nonpolar molecule, has only dispersion forces, i.e. van der Waals forces.

Water, on the other hand, is a polar molecule, having dispersion as well as dipole-dipole forces. In addition, having a highly-electronegative atom on it attached to an #"H"# atom, it also "hydrogen-bonds" to other water molecules.

The trade in energy sucks for #"H"_2# (but not so much for water), so the #"H"_2cdots"H"_2"O"# interaction is highly unfavored for #"H"_2#, compared to the #"H"_2cdots"H"_2# and #"H"_2"O"cdots"H"_2"O"# interactions.

So, #"H"_2# is very poorly soluble in water. Its solubility at #"1 atm"# at #20^@ "C"# is #"0.00016 g H"_2/"100 g water"#.

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