### Moles: Concentration and titration calculations

Understanding how to use moles to find the concentration of solutions, and how to deal with titration calculations.

### Test yourself: Have you mastered the equation?

Make sure you have a copy of the periodic table (or open the periodic table window on this site).

2.00 moles of sodium chloride is dissolved in water and made up to 250cm3 of solution. What is the concentration of the solution (mol dm−3)?

Concentration (mol dm−3) = moles (mol) / volume of solution (dm3)

Concentration = 2.00 / 0.250 = 8.00 mol dm−3

15.0g of magnesium chloride is dissolved in water and made up to 250cm3 of solution. What is the concentration of the solution (mol dm−3) to 3 sf?

Moles = mass / molar mass = 15.0 / 95.21 (MgCl2) = 0.1575464 mol

Concentration (mol dm−3) = moles (mol) / volume of solution (dm3)

Concentration = 0.1575464 / 0.250 = 0.6301859 mol dm−3 = 0.630 mol dm−3 (3sf)

How many moles (3sf) of sodium hydroxide is dissolved in 500cm3 of a solution of concentration 0.800 mol dm−3?

Moles (mol) = concentration (mol dm−3) × volume of solution (dm3)

Moles = 0.800 × 0.500 = 0.400 mol (3sf)

What mass, in g (3sf), of potassium hydroxide is dissolved in 250cm3 of a solution of concentration 0.600 mol dm−3?

Moles (mol) = concentration (mol dm−3) × volume of solution (dm3)

Moles = 0.600 × 0.250 = 0.150 mol

Mass = moles × molar mass = 0.150 × 56.11 (KOH) = 8.4165 = 8.42g (3sf)

A student takes 150 cm3 of a 1.75 mol dm−3 aqueous solution and dilutes it with water to 500cm3 in a volumetric flask. What is the concentration of the new solution (mol dm−3) to 3sf?

Moles (mol) = concentration (mol dm−3) × volume of solution (dm3)

Moles in the sample of original solution = 1.75 × 0.150 = 0.2625 mol

Concentration (mol dm−3) = moles (mol) / volume of solution (dm3)

Concentration of the new solution = 0.2625 / 0.500 = 0.525 mol dm−3

0.450 moles of sodium hydroxide is dissolved in water and made up to 750cm3 of solution. What is the concentration of the solution in g dm−3 (3sf)?

Concentration (mol dm−3) = moles (mol) / volume of solution (dm3)

Concentration = 0.450 / 0.750 = 0.600 mol dm−3

Converting moles to mass: mass = moles × molar mass = 0.600 × 40.00 = 24.0g

Concentration = 24.0 g dm−3