**Molar Concentration**

A molar concentration, often denoted by the symbol [M], is a unit of measurement for the concentration of a chemical species in solution. It is defined as the number of moles of that species present in one litre of solution.

[M] = moles of solute/litres of solution

[M] = n/v

Molar concentration can be calculated from the amount of substance dissolved in a given volume of solution or vice versa. It is most frequently expressed in moles per litre (mol/L) units.

Molar concentration is sometimes called molarity, but this term is less preferred due to ambiguity with the SI unit molality.

**About the Topic**

One mole of a substance is defined as the amount of that substance that contains Avogadro’s number of molecules.

For example, one mole of water contains 6.022×1023 molecules of water. Therefore, the molar concentration of a solution is the number of moles of the dissolved substance per litre of solution.

Molar concentration can be calculated from the amount of substance dissolved in a given volume of solution or vice versa. To calculate the Molarity of a solution, the number of moles of the dissolved substance must first be determined.

Concentration can also be expressed as a mass concentration, the mass of a substance per unit volume of solution.

**Molarity of a Solution**

The molarity of a solution can also be expressed as a percent concentration by mass (% w/v). This is the mass of a substance per 100 mL of solution. To convert from molarity to percent concentration by mass, the following formula can be used:

The formula for molarity is M = moles of solute/litres of solution.

For example, a 1 M NaCl solution would have a percent concentration by mass of 58.44% w/v.

**Solved Examples**

**Calculate the molar concentration of a 10.0 M solution of NaCl?**

The molar concentration of a 10.0 M solution of NaCl would be 10.0 M. To convert from molarity to percent concentration by mass, the following formula can be used:

Molarity x Volume = Concentration

10.0 M x 1 L = 10.0 M

10.0 M x 100 mL = 1,000 mL

1,000 mL = 1 L

Therefore, the percent concentration by mass of a 10.0 M NaCl solution would be 1,000 mL/L or 100% w/v.

**The concentration of**Ca(HCO3)2**is 0.85 gmol/L. Convert this concentration into geq/L.**

Given that:

Concentration, [C] = 0.85 gmol/ L

[C]eq = [C][MM] / equation mass

MM = 40.1(2) + 2{1+12+3(16)}

= 202.2

Total Number of species = 2

Therefore, equation mass = Ca(HCO3)2 / 2

= 202.2 / 2

[C]eq = 0.85[202.2] / 202.2/2

= 1.7 geq/L