Most common electrolytes in water

What are the most common electrolytes in water?

Water is an ionic compound. Therefore, in liquid state, it is a good solvent for compounds with ionic character. 

Compounds that dissolve in water can be classified into electrolytes and non-electrolytes. Electrolytes are molecules with at least one ionic bond, which when dissolved dissociate into a cation, positively charged, and a anion, negatively charged.





Non-electrolytes dissolve without dissociating; they are dissolved without a charge and do not add conductivity to the water.

Water without electrolytes does not conduct electricity: it is a dielectric.

water chemistry studies the interaction between water and the compounds that dissolve in it.

Ionic compounds that dissolve in water can be solids, liquids or gases at the conditions of the Earth.

When water comes into contact with the earth, it dissolves mainly ionic compounds. For example: NaCl, CaCO3 okay2SO4. Each of these compounds will dissolve in an amount that will depend on the time of contact with water and its solubility at the prevailing temperature. 

Some ionic compounds in liquid state that dissolve in (or mix with) water would be H2SO4, HNO3.

Water dissolves or absorbs gases like HCl, SO2, CO2, H2S. In doing so, these form: H3O+(hydronium ion), Cl (chlorides), SO4-2(sulfates), HCO3(bicarbonates) and S-2 (sulfides).

The most common cation and anion in water found in natural bodies (seas, lakes, rivers, wells) are:


The most common cation:

Na+ (sodium)

The most common anion:

Cl (chloride)

The cations and anions that include what is known as physicochemical analysis of the water are:


The sum of the following two cations is known as total hardness:

Ca+2 (calcium)

Mg+2 (magnesium)

The concentration of this cation is measured through what is called the pH, and has an absolute dependence relationship with the concentration of the OH anion:

H3O+ or H+ (hydronium or hydrogen)

The sum of the next three anions is known as total alkalinity:


CO3-2 (carbonates)

OH (hydroxides)


Other typical cations and anions in waters of natural origin


Two cations that usually represent a problem.

They can be retained by oxidation. The reaction is slow, but can be accelerated by MnO2 as a catalyst:

Fe+2(iron or iron)


Others (just a few examples):

K+ (potassium)

Pb+2 (lead)

Cu+2 (copper)

Zn+2 (zinc)

NH4+ (ammonium)

An anion that usually represents a problem whose solution is not cheap:

F (fluorides)

An anion that also often represents a problem, which is solved by oxidation that is catalyzed on an MnO surface2 (the same one used to accelerate the oxidation reaction of Fe+2 and Mn+2):

S-1 (sulfides)

Others (just a few examples):

SO4-2 (sulfates)

DO NOT3 (nitrates)

PO4-3 (phosphates)


The most used reference to analyze a water is the well-known Standard Methods [Standard Methods for the Examination of Water and Wastewater, sponsored by three coordinated US agencies:  American Public Health Association (APHA), American Water Works Association (AWWA) and Water Environment Federation (WEF)].

The physicochemical analysis of a water provides essential information to predict its behavior and to address a suitable or necessary treatment. It comprises the following analyzes:

  1. Total dissolved solids (mg / L).
  2. Total hardness (mg as CaCO3/ L or meq / L).
  3. Total alkalinity (mg as CaCO3/ L or meq / L).
  4. pH (dimensionless; it has values between 0 and 14).

In water chemistry, mg / L is not the same as ppm.

When the concentration of a compound dissolved in water is reported, it is not the same to speak of ppm (parts per million) than of mg / l.

In the case of liquids and solids, the ppm they refer to the number of milligrams of the compound whose concentration is reported, between one million milligrams of the solution (if it is a liquid) or of the mixture (if it is a solid). This is the same as the number of mg of the compound in 1 kg of the solution or mixture.

In the case of gases or vapors, the concentration of a compound, reported in ppm, means the number of moles of the compound, per one million moles of the mixture. At not very high pressures, this is the same as the number of milliliters of the compound, per one liter of the mixture (that is, per one million milliliters of the mixture).

If the density of water were exactly 1.0000 g / cm3, then it would be exactly the same ppm as mg / L. The density of totally pure water at 20 ° C is 0.9999 g / cm3. This changes with temperature or with the presence of dissolved compounds in the water.

When talking about the concentration of a compound in water, as long as the concentration of the total dissolved compounds is not high and as long as the temperature is not far from 20 ° C, the ppm is close to mg / L, but they are not identical. .

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