Molarity Of Solutions Calculations Chemistry Tutorial - AUS-e-TUTE

Amount of Substance Concentration (Molarity) Calculations Chemistry Tutorial

Key Concepts

⚛ Concentration of a solution refers to the amount of solute dissolved in a given solvent to make a solution. When water is the solvent, the formula of the solute is immediately followed by aq enclosed in round brackets, (aq).

term	description	example
solute	substance that dissolves	solid sodium chloride, NaCl(s)
solvent	substance that enables solute to dissolve	liquid water, H2O(l)
solution	homogeneous mixture of solute dissolved in solvent	sodium chloride dissolved in water, NaCl(aq)

⚛ Concentration of a solution can be given in moles of solute per litre of solution (mol L-1 or mol/L or M), or, in moles of solute per cubic decimetre of solution (mol dm-3 or mol/dm3)(1)

solute	solution
units of measurement (symbol)	moles (mol)	moles per litre (mol L-1 or mol/L or M)
units of measurement (symbol)	moles (mol)	moles per cubic decimetre (mol dm-3 or mol/dm3)

⚛ Molarity is the term used to describe a concentration given in moles per litre.

Alternative names for molarity are · amount of substance concentration (IUPAC preferred term) · amount concentration · molar concentration

⚛ Amount of substance concentration, molarity, has the units mol L-1 (or mol/L or M) or the equivalent SI units of mol dm-3 (mol/dm3)

⚛ Amount of substance concentration, molarity, the concentration of a solution in mol/L, mol L-1, mol dm-3 or mol/dm3, is given the symbol c (sometimes M).

For a 0.01 mol L-1 HCl(aq) solution we can write :

(i) [HCl(aq)] = 0.01 mol L-1 = 0.01 mol dm-3 = 0.01 M (amount concentration implied by square brackets around solvated solute formula)

(ii) c(HCl(aq)) = 0.01 mol L-1 = 0.01 mol dm-3 = 0.01 M (c stands for amount concentration, solvated solute formula given in round brackets or parentheses)

⚛ Mathematical equation (formula or expression) to calculate the molarity of a solution (concentration in mol L-1) is

c = n ÷ V

c = concentration of solution in mol L-1 (mol/L or M) n = amount of substance being dissolved (moles of solute) V = volume of solution in litres (L) or cubic decimetres (dm3)

⚛ This equation (formula or expression) can be re-arranged to find:

(i) moles of solute given molarity and volume of solution:

n = c × V

(ii) volume of solution given moles of solute and molarity:

V = n ÷ c