The chemical formulas of ternary salts conserve the anion of their precursor ternary acid (oxoacid), exchanging the H + for a metal cation or for the ammonium ion (NH 4 + ). In other words, in an oxo acid with the simple formula HAO, its ternary salt will have the formula MAO.
An illustrative example is in the case of the substitution of the two acidic protons of H 2 SO 4 (sulfuric acid) by the cation Cu 2+ . Because each proton adds a +1 charge, the two protons equal the +2 charge on the copper ion. Then there is CuSO 4 , whose corresponding nomenclature is copper (II) sulfate or cupric sulfate.
There are many methods and mnemonics for memorizing and learning the nomenclature of ternary salts.
The first confusions can originate because it varies, either by the valence of the metal M or by the oxidation state of the non-metallic element.
However, the number of O atoms in the anion is very useful when naming them. This anion, coming from the precursor ternary acid, defines a large part of the nomenclature.
For this reason, it is advisable to first remember the nomenclature of certain ternary acids, which serve as a support to name their salts.
The nomenclature of some ternary acids with suffix “ico”, and the corresponding oxidation number of the central element, are:
H 3 BO 3 – Boric acid.
H 2 CO 3 – Carbonic acid.
H 4 SiO 4 – Silicic acid.
HNO 3 – Nitric acid.
H 3 PO 4 – Phosphoric acid.
H 3 AsO 4 – Arsenic acid.
HClO 3 – Chloric acid.
HBrO 3 – Bromic acid.
HIO 3 – Iodic acid.
H 2 SO 4 – Sulfuric acid.
H 2 SeO 4 – Selenic acid.
H 6 TeO 6 – Telluric acid.
The oxidation states (+3, +4, +5 and +6) are equal to the number of the group to which the elements belong.
So up to group 7A (17) of halogens, which do not comply with the rule of ternary acids “ico”. When these have oxidation states of +7, the prefix “per” is added to their “ico” acids.
Number of oxygen atoms
By memorizing the above ternary acids “ico”, the nomenclature is modified according to the increasing or decreasing number of O atoms.
If there is a lesser unit of O, the acid changes the suffix “ico” to the suffix “bear”; and if there are two units less, the name additionally adds the prefix “hiccup”.
For example, for HIO 2 nomenclature is acid yod bear ; for HIO, acid hypo yod bear ; and HIO 4 , acid per Yod ico .
So, to name the ternary salts, the anions of the “ico” acids are changed with the suffix to “ato”; and for those with the suffix “bear”, they are changed to “ito”.
Returning to the example of iodic acid HIO 3, changing the H + by sodium Na + , it has the name of the ternary salt: yod ato sodium, NaIO 3 .
In the same way, for iodous acid HIO 2 , its sodium salt is yod ito sodium (NaIO 2 ); for hipoyoso acid HIO is hypo yod ito sodium (NaIO or Naoi); and periodic acid, per yod ato sodium (NaIO 4 ).
The same applies to the rest of the “ico” acids listed by the oxidation states mentioned above, under the limitation that the prefix “per” occurs in those salts with a higher O unit (NaClO 4 , per sodium chlorate ).
For example, carbonic acid H 2 CO 3 can lose a single proton per sodium, remaining as NaHCO 3 . For these acid salts, the recommended nomenclature is to add the word “acid” after the name of the anion.
Thus, the salt is referred to as: sodium acid carbonate . Here again the suffix “ico” is changed to the suffix “ato”.
Another unconventional rule, but very popularly accepted, is to add the prefix “bi” to the name of the anion to indicate the existence of an acidic proton. This time, the name of the salt above is mentioned as: sodium bi carbonate.
If all the protons are replaced by Na + cations , neutralizing the two negative charges of the carbonate anion, the salt is simply referred to as sodium carbonate, Na 2 CO 3 .
Valencia of metals
Knowing the anion in the chemical formula, the valence of the metal in the ternary salt can be calculated arithmetically.
For example, in FeSO 4 it is now known that sulfate comes from sulfuric acid, and that it is an anion with two negative charges (SO 4 2- ). Thus, to neutralize them, iron must have two positive charges, Fe 2+ .
Therefore, the name of the salt is iron (II) sulfate. The (II) reflects the valence 2, equal to the positive charge +2.
When metals can only have one valence – as in the case of group 1 and 2 – the addition of the Roman numeral is omitted (it is incorrect to say sodium carbonate (I)).
Properties of ternary salts
They are predominantly ionic, crystalline compounds, with intermolecular interactions governed by electrostatic forces, which results in high melting and boiling points .
Because they have negatively charged oxygen, they can form hydrogen bonds in aqueous solution, dissolving their crystals only if this process benefits the ions energetically; otherwise, the ternary salt remains insoluble (Ca 3 (PO 4 ) 2 , calcium phosphate).
These hydrogen bonds are responsible for the hydrates of these salts, and these water molecules are known as water of crystallization.
Examples of ternary salts
Ternary salts occupy a place in daily life, enriching food, medicine or in inanimate objects such as matches and a fire extinguisher.
For example, the freshness of fruits and vegetables is preserved for longer periods by the action of sodium sulphite and sodium acid sulphite (Na 2 SO 3 and NaHSO 3 ).
In red meat, its red meat is preserved by the additives of sodium nitrate and nitrite (NaNO 3 and NaNO 2 ).
Also, in some canned products the unpleasant metallic taste is counteracted by sodium phosphate additives (Na 3 PO 4 ). Other salts, such as FeSO 4 , CaCO 3 , Fe 3 (PO 4 ) 2 , are also found in cereals and breads.
Carbonates are the chemical agent in fire extinguishers, which at high temperatures produce CO 2, smothering the fire.
Additional ternary salts
- Ba (NO 3 ) 2.
- (NH 4 ) 3 PO 4.
- SrSO 4.
- KClO 3.
- CaCrO 4 (calcium chromate).
- KMnO 4 (potassium permanganate).