Salts and electrolytes as acid or base
When substances are composed of ions, we often call them electrolytes.
The word has to do with the property of ionic substances (there are charged particles present!) to conduct electrical current (see module 5),
at least when those particles can move freely (are not hold in an ionic lattice).
Electrolytes are salts in the first place, but also other substances with ions, like acids and bases (certain when they contain OH-), belong to the electrolytes.
If a reaction takes place with ionic substances (substances with ions), then you can write the reaction equation in ionic formulas, but also in empiric formulas. We prefer here the ionic formulas.
Only when you must execute calculations on basis of the reaction equation, then it is better to work with empiric formulas.
Example: In that case do not use Na+ and Cl-, but NaCl.
Example:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) empiric formulas
H3O+ + OH- → H2O(l) ionic formulas
The two equations represent exactly the same process.
The substances built up of ions, carry the character of those ions; you must consider any ion.
An ion has a neutral or an acid or a basic character. The dominant character determines the final character of the salt as a whole.
In the case of NaCl, built up of the ions Na+ and Cl- not any of the ions has an acid of basic character.
The salt as a whole must be a neutral substance; does not influence the pH of its solution.
But many other salts do have that influence: like Sodium carbonate, built up of ions Na+ and CO32-.
Analysis shows that the first ion is neutral, but the second is rather basic.
A solution of this salt wil have a pH above 7. The solution will be basic.
Copper(II)sulfate contains ions of sulfate (very weak basic) and ions of Copper(II) (rather acid).
In a solution of this copper sulfate, the acid character will dominate.
Copper(II)sulfate will cause in the solution a pH lower then 7.
Concluding: You must consider any ion apart, and analyse and compare.
Examples:
Use table I
We have a solution of Sodium Hydrogen carbonate in water. Let's analyse this solution:
First you must know that all salts with Sodium ions are soluble in water. Our salt will dissociate in ions:
Na+ and HCO3-; these ions remain hydrated in water.
Na+ with its charge of +1 will have no influence on the water molecules, does not cause any formation of protons and does not influence the pH of the water.
HCO3- is another story:
The table shows a KA = 10-10 and a KB of 10-8
KA (10-10) < KB (10-8), so, HCO3- has an amphoteric character, where the basic character dominates, because KB > KA.
The ion remains in the water with a basic character, and the solution of the salt NaHCO3 in water is not neutral,
but will have a pH above 7 (somewhere between 8 and 10, depending on the amount of salt).
In this way you must be able to analyse any (salt)solution in water.
Connected to this topic, it remains important to check the solubility of the salt.
The active ions must really be present in the solution for influencing the pH in that solution.
A very bad soluble salt does not deliver enough ions to have direct influence. Apart from the table with acids and bases, you must also consult the table with solubility of salts to make sense.