What is Molar Concentration?

Molar Concentration, or molarity is an amount of substance, or solute in a given volume of solution. It is usually expressed in moles per liter (mol/L). To understand molarity, one of the basic concepts in physics that helps analyze fluids' behavior and chemical reactions.

Formula of Molar Concentration

The formula of molar concentration is,

 

Where:

• C = Molar concentration (mol/L)

• n = Number of moles of solute (mol)

• V = Volume of solution (L)

Solved Examples

Example 1:Determine the molar concentration of NaOH for the reaction between HCl and NaOH.

Solution:

The balanced chemical equation can be written as,

HCl + NaOH → NaCl + H2O

For an acid 

n(HCl) = (35.0 / 1000 dm3) × 0.250 mol dm-3

= 8.75 × 10-3mol

The mole ratio NaOH: HCl = 1:1.

The moles of NaOH present is 8.75 × 10-3mol.

Now we have the equation,

 

Now convert the volume of aqueous NaOH in dm3

 25 cm3 = 25 / 1000 dm3

              = 25 × 10-3dm3

Thus,

 Molar concentration of NaOH   = 8.75×10−3 / 25.0×10-3

 Molar conc. of NaOH = 0.350 mol dm-3

Example 2: The conc. of Ca(HCO3)2 is 0.85 gmol/L. Express this conc. in geq/L.

Solution:

Given,

[C] = 0.85 gmol/ L

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

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

    = 202.2

Number of reference species = 2

Therefore, eq.mass = Ca(HCO3)2 / 2

                                = 202.2 / 2

However,

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

          = 1.7 geq/L

 

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