Hydroxides Nomenclature

Hydroxides are a group of compounds not well known in general, although you might know them by their commercial name in some cases.

Copper Hydroxide

                

Sodium Hydroxide

 

Some Hydroxides are present on drain cleaners; some are used on making soap and detergents.

Hydroxides are formed when Metal Oxides react with Water.

CaO + H₂O ---> Ca(OH)₂

Hydroxides have this writing structure:

Metal OH

And like with Oxides we just need to figure out the subscripts A,B.

Metal_A (OH)_B

For Hydroxides the (OH) radical works with -1. Now you write the oxidation number of the metal and the valence of the OH radical.

Now you just have to SWITCH the numbers like this and you are done, know you know how to make Hydroxides. Metal oxidation numbers can be found here

Never write the subscript of the OH radical WITHOUT ( ).

HYDROXIDE NOMENCLATURE

There are 3 ways of naming Hydroxides.

• TRADITIONAL nomenclature
• IUPAC nomenclature
• STOCK nomenclature

TRADITIONAL NOMENCLATURE

You need to learn a little system of prefixes and suffixes (for the oxidation numbers)

• If it only has 1 oxidation number there isn’t a suffix to use, some people use the –ic suffix.

• If it has 2, the higher is –ic and the lower is –ous.

-ous	-ic
+2	+3
+1	+2

Note that the suffix does not depend on the number but on how many valences the element has. I’ve seen people making the mistake to think that +2 is always –ous or always –ic.

EXAMPLE

Name this Hydroxide

Fe(OH)₃

Remember how to make hydroxide formulas? Now we just need to go backwards to figure out which oxidation number the metal is using.

Now that we know which it is, let’s find the correct suffix to use. It has 1 oxidation numbers:

+2 ----> -ous

+3 ----> -ic

Traditional nomenclature has this writing structure:

[ELEMENT NAME][SUFFIX] Hydroxide

So we just need to fill the name of the metal and the suffix

Ferric Hydroxide

Be careful with some element names, some aren’t use in nomenclature, such as IRON (Fe): so it wouldn’t be IRONIC (heheh), but FERRIC.

IUPAC NOMENCLATURE

This one is the easiest in my opinion, it is also called “systematic”; you just need to learn these prefixes:

Number	Prefix
1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-
7	hepta-
8	octa-
9	nona-
10	deca-

EXAMPLE:

Fe(OH)₃

You just need to use the prefixes to name the element according of the subscripts.

 In this case the structure of IUPAC nomenclature is

[PREFIX][ELEMENT NAME]  [PREFIX]Hydroxide

So this is the name of the oxide according to IUPAC Nomenclature (if the metal has a subscript of one we don’t use MONO, we only use MONO if the radical OH has 1 as subscript):

Iron triHydroxide

STOCK NOMENCLATURE

This is an easy nomenclature as well; you don’t have to know anything else but the oxidation numbers of the elements.

EXAMPLE:

Fe(OH)₃

First step is to figure out the oxidation number of the metal:

 The structure of STOCK nomenclature is

[ELEMENT NAME][OX. NUMBER]     Hydroxide

The oxidation number of the metal has to be written in Roman numbers (I, II, III, IV, etc.).

This is the name according to Stock Nomenclature:

Iron(III) Hydroxide

Be careful with writing a space between the name and the Roman number, there isn't one.

Coming up! Hydroxides Exercises