Basic salts contain the OH – anion in their solids. For example, alkali hydroxides, such as sodium and potassium, NaOH, and KOH, are considered members of these salts; although they are extremely caustic, which is why they deserve the denomination of hydroxides instead of being called salts.
Other basic salts, on the other hand, have anions such as carbonate, CO 3 2- . Carbonate is derived from carbonic acid, H 2 CO 3 , a weak acid. Therefore, carbonate salts, such as calcium carbonate used in antacids, are classified as basic salts. The same reasoning applies to sodium bicarbonate, NaHCO 3 , and to all other bicarbonate salts.
Basic salts have two definitions that complement each other: they contain OH – anions in their solids, or they generate these same hydroxyl anions once their crystals dissolve in water.
Regardless of which definition is chosen, the pH of your aqueous solutions will be greater than 7, and therefore, they will be alkaline or basic.
General formula of basic salts
Having clarified what is meant by basic salt, its formula, although not strictly general, is as follows:
M n (OH) w XO v
Where M is the metal or ammonium cation, OH the hydroxyl anions, and XO the anion derived from a weak or strong acid. The subscripts n , w, and v indicate how many M, OH, and XO, respectively, make up the basic salt, as well as their proportions.
Note that v can be equal to zero, which means that we have an alkaline or alkaline earth hydroxide. This is what happens with NaOH and KOH. Similarly, w can be zero, which means that there are no OH – ions . For example, CaCO 3 does not have OH – , and yet it is still a basic salt.
From the above it is concluded that the general formula of basic salts is M n (OH) w XO v , but not all salts comply with this. Therefore, a more important factor to consider is the nature of the XO anion. Thus, it will be known when a salt is basic, regardless of whether or not it has OH – ions in its formulas.
The basic salts are dissolved in water following the following equation:
M n (OH) w XO v (s) → n M + (ac) + w OH – (ac) + v XO – (ac)
Note that when it dissolves it releases the OH – ions into the water. This affects the pH of the solution, becoming alkaline with a value higher than 7. For example, basic calcium nitrate dissolves in water according to the following:
Ca (OH) NO 3 (s) → Ca 2+ (aq) + OH – (aq) + NO 3 – (aq)
The values of n , w, and v are equal to 1 for this salt.
On the other hand, basic salts that do not have OH – , but do have an anion derived from a weak acid, are hydrolyzed in water:
CaCO 3 (s) → Ca 2+ (aq) + CO 3 2- (aq)
CO 3 2- (aq) + H 2 O (l) ⇌ HCO 3 – (aq) + OH – (aq)
Note that the product of this hydrolysis is an OH – anion . Hence the alkalinity of these bases. However, and as expected, they are less basic than those that already have OH – ions present in their crystals. For example, NaOH is extremely basic:
NaOH (s) → Na + (aq) + OH – (aq)
Well, it releases the OH ions – it just touches the water directly; Or worse yet, it barely touches the skin’s moisture.
The other physical or chemical properties of the basic salts do not differ too much from those of other neutral or acid salts.
The nomenclature of the basic salts depends on the nature of the XO anion: if it is monatomic, or if it is an oxoanion. However, this section will focus especially on basic salts with OH – anions . Those that do not have them have nomenclatures much easier to memorize or reason.
With monatomic anions
Monatomic anions are not represented as XO, but as X. They are derived from a hydracid HX, such as hydrofluoric acid, HF, or hydrochloric acid, HCl, and so on.
In these cases, they are systematically named in two ways:
(Numeral prefix except mono) hydroxy + name of the anion ending with the suffix –uro + name of the metal with its valence in parentheses (if it has more than one)
For example, the Ni (OH) Cl salt is called nickel (II) hydroxychloride.
Name of the anion with the ending –uro + – (numeral prefix except mono) hydroxide + name of the metal and its valence in parentheses
For example, the Ni (OH) Cl salt can also be named nickel (II) chloride hydroxide.
We also have the traditional nomenclature, sometimes mixed with the systematic:
Name of the anion followed by (numeral prefix except mono) basic and the name of the metal with the suffixes –oso or –ico as applicable.
For example, Ni (OH) Cl is called basic nickel chloride, or basic nickel (II) chloride.
The systematic nomenclature for the basic salts that have oxoanions is a bit more complicated. However, the simplest version is built as follows:
(Prefix) hydroxide- (name of the anion) + de + name of the metal and its valence in parentheses
For example, Fe (OH) NO 3 is called: iron (II) hydroxide-nitrate.
Likewise, there is the traditional nomenclature:
Anion name + (numeral prefix) basic + of + metal name ending in –oso or –ico
Thus, Fe (OH) NO 3 is called: ferrous basic nitrate, or basic iron (II) nitrate.
Basic salts are the product of acid-base neutralizations, specifically between a hydracid or an oxoacid with an excess of a base or hydroxide:
Base (excess) + acid → basic or alkaline salt + water
For example, Ca (OH) NO 3 is formed by neutralizing nitric acid with an excess of calcium hydroxide:
Ca (OH) 2 (excess) + HNO 3 → Ca (OH) NO 3 + H 2 O
Another training example would be the following:
Fe (OH) 3 (excess) + H 2 SO 4 → Fe (OH) SO 4 + 2H 2 O
This salt is called: basic ferric sulfate, basic iron (III) sulfate, or hydroxide-iron (III) sulfate.
Examples of basic salts
Finally, some other examples of basic salts will be listed together with their simplest names:
-NaCH 3 COO: sodium acetate
-Na 2 S: sodium sulfide
-KCN: potassium cyanide
-MgCO 3 : magnesium carbonate
-Fe (OH) SO 3 : basic iron (III) sulfite
-Fe (OH) (C 6 H 5 COO) 2 : basic iron (III) benzoate
-AuCl (OH) 2 : dibasic gold (III) chloride
-CuClO 3 (OH): basic copper (II) chlorate
-Al (OH) SO 4 : basic aluminum sulfate
-Pb (OH) 2 CO 3 : lead (IV) dibasic carbonate
The problem with basic salts is that not all of them can be prepared, since an excess of base or hydroxide is not enough to crystallize them without resorting to other processes. This is the case with Pb (OH) 2 CO 3 . However, this carbonate does exist as a white lead (II) pigment, whose formula is 2PbCO 3 · Pb (OH) 2 or Pb 3 (OH) 2 (CO 3 ) 2 .