Posts Tagged ‘Properties of water’

Autoionization of hydrogen fluoride.

Sunday, April 24th, 2016

The autoionization of water involves two molecules transfering a proton to give hydronium hydroxide, a process for which the free energy of reaction is well known. Here I ask what might happen with the next element along in the periodic table, F.


Deuteronium deuteroxide. The why of pD 7.435.

Friday, April 22nd, 2016

Earlier, I constructed a possible model of hydronium hydroxide, or H3O+.OH– One way of assessing the quality of the model is to calculate the free energy difference between it and two normal water molecules and compare the result to the measured difference. Here I apply a further test of the model using isotopes.


Oxane oxide: a tautomer of hydrogen peroxide.

Friday, April 15th, 2016

If H3N+-O is viable compared with its tautomer H2N-OH when carrying water bridges, then why not try H2O+-O vs HO-OH?


Azane oxide, a tautomer of hydroxylamine.

Friday, April 15th, 2016

In the previous post I described how hydronium hydroxide or H3O+…HO, an intermolecular tautomer of water, has recently been observed captured inside an organic cage[1] and how the free-standing species in water can be captured computationally with the help of solvating water bridges. Here I explore azane oxide or H3N+-O, a tautomer of the better known hydroxylamine (H2N-OH).



  1. M. Stapf, W. Seichter, and M. Mazik, "Unique Hydrogen-Bonded Complex of Hydronium and Hydroxide Ions", Chemistry - A European Journal, vol. 21, pp. 6350-6354, 2015.

Hydronium hydroxide: the why of pH 7.

Thursday, April 14th, 2016

Ammonium hydroxide (NH4+…OH) can be characterised quantum mechanically when stabilised by water bridges connecting the ion-pairs. It is a small step from there to hydronium hydroxide, or H3O+…OH. The measured concentrations [H3O+] ≡ [OH] give rise of course to the well-known pH 7 of pure water, and converting this ionization constant to a free energy indicates that the solvated ion-pair must be some ~19.1 kcal/mol higher in free energy than water itself. So can a quantum calculation reproduce pH7 for water?


How many water molecules does it take to form ammonium hydroxide from ammonia and water?

Sunday, March 20th, 2016

This is a corollary to the previous post exploring how many molecules are needed to ionise HCl. Here I am asking how many water molecules are required to form the ionic ammonium hydroxide from ammonia and water.