Profile
Settings
Refer your friends
Sign out
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
