Sciencemadness Discussion Board

Metal Oxides in water

Fifth_Ghost - 28-1-2018 at 05:22

Part of my job I work with metal oxides. Commonly there is a desire to use DI as a solution medium. With that I have learned the following rules and have a question. Is this true for all cases?

Metal oxides of with a +1 or +2 charge hydrolyze when combined with water, immediately becoming a basic solution. Metal oxides of +3 charge are hygroscopic absorbing water until it is inundated. Then the +3 metal oxide hydrolyzes making a somewhat basic solution. Metal Oxides with +4 to +7 might have hygroscopic tendencies, but will not hydrolyze under normal conditions.

unionised - 28-1-2018 at 06:04

It is very rare to find any rules in chemistry that have no exceptions.
The alkaline earth metals form oxides that react with water (and where the metal has a +2 charge).
However copper, iron, nickel etc form insoluble oxides with +2 charges on the metal ions.
Copper and silver both form oxides with +1 charges which are insoluble in water.
There aren't many +7 oxides (and most of them are not nice to work with).
I'm fairly sure that they will react with water to form the corresponding acids.

If you are looking for a general rule it's probably more nearly true that higher oxidation states tend to dissolve better in alkaline solutions whereas lower oxidation states tend to dissolve better in acid conditions.


What are you actually seeking to do?

Fifth_Ghost - 28-1-2018 at 06:49

I am seeking to expand my understanding of metal oxides in water.

symboom - 28-1-2018 at 08:33

Vanadium(V) oxide dissolves slightly in water 8.0 g/L
Chromium trioxide is souble 169 g/100 mL
These two are souble oxides

DraconicAcid - 28-1-2018 at 10:36

Quote:
Part of my job I work with metal oxides. Commonly there is a desire to use DI as a solution medium. With that I have learned the following rules and have a question. Is this true for all cases?

Metal oxides of with a +1 or +2 charge hydrolyze when combined with water, immediately becoming a basic solution.


True for soluble metal oxides such as those of the alkali metals and alkaline earth metals. Transition metal oxides of +1 or +2 charge (copper(I), silver, copper(II), zinc, nickel(II), etc) are not sufficiently soluble to change the pH of the water.
Quote:
Metal oxides of +3 charge are hygroscopic absorbing water until it is inundated. Then the +3 metal oxide hydrolyzes making a somewhat basic solution.


Most +3 metal oxides are basically rocks, generally not hygroscopic, and will not change the pH of the solution. They will react to neutralize strong acid solution; how quickly this happens will generally depend on the degree of calcination of the oxide. Some of them will also react with strong base to form complex anions (chromium, aluminum are classic examples).
Quote:
Metal Oxides with +4 to +7 might have hygroscopic tendencies, but will not hydrolyze under normal conditions.


Mn2O7 will hydrolyze rapidly to give permanganic acid. Chromium trioxide gives chromic acid.

Edit by Texium: Fixed broken quote

[Edited on 1-28-2018 by Texium (zts16)]

AJKOER - 29-1-2018 at 05:05

Formulating rules with respect to the chemical inertness of metal oxides is even more problematic if one is inclusive of nano oxides, like nano-ferric oxide. Broad range of their application suggests significant reactivity differences, as for example, from Wikipedia (https://en.wikipedia.org/wiki/Iron_oxide_nanoparticle ):

"Applications of iron oxide nanoparticles include terabit magnetic storage devices, catalysis, sensors, Superparamagnetic Relaxometry (SPMR), and high-sensitivity biomolecular magnetic resonance imaging (MRI) for medical diagnosis and therapeutics. These applications require coating of the nanoparticles by agents such as long-chain fatty acids, alkyl-substituted amines and diols."