# 4.2.10 Titration Calculations

Higher Tier Only

### Titration Calculations

• Once a titration is completed and the average titre has been calculated, you can now proceed to calculate the unknown variable using the formula triangle as shown below Formula triangle showing the relationship between concentration, number of moles and volume of liquid

#### Worked Example

A solution of 25.0 cm3 of hydrochloric acid was titrated against a solution of 0.100 mol dm-3 NaOH and 12.1 cmwere required for complete reaction.

Determine the concentration of the acid.

Step 1: Write the equation for the reaction:

HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)

Step 2: Calculate the number of moles of the NaOH

Moles = (volume ÷ 1000) x concentration

Moles of NaOH = 0.012 dm3 x 0.100 mol dm-3 = 1.21 x 10-3 mol

Step 3: Deduce the number of moles of the acid

Since the acid reacts in a 1:1 ratio with the alkali,  the number of moles of HCl is also 1.21 x 10-3 mol

This is present in 25.0 cm3 of the solution

Step 4: Find the concentration of the acid

Concentration = moles ÷ volume

Concentration of HCl =1.21 x 10-3 mol  ÷ 0.025 dm3 = 0.0484 mol dm-3 ### Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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