Volumetric analysis

The calculation should be carried out in a logical order as follows:

1. Write the balanced equation for the reaction between the standard and the test substance.
2. From the stoichiometry of the reaction, determine how many moles of the test substance react with 1 mole of the standard substance. For example, in the reaction between an H₂SO₄ standard solution and an NaOH test solution:
   ⇒Equation [21.2]
   H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
   Therefore 2 moles of NaOH react with 1 mole of H₂SO₄.
3. Calculate the number of moles of standard substance used to reach the end-point of the reaction. This can be determined from knowledge of the concentration of the standard solution (mol L⁻¹) and the volume of titrant used (mL). Remember to take care with units - in this instance division by a factor of 1000 is required to convert mL to L:

   Number of Moles =	concentration (mol L−1) × volume (mL)
   	1000

   
   
4. The number of moles of test substance present in the titrand is then obtained from knowledge of the equivalences. In the example given above (point 2) the number of moles of test substance is twice the number of moles of standard substance. Therefore, if X moles of H₂SO₄ are used (as calculated in point 3), 2X moles of NaOH were present in the initial volume of test solution.
   
5. Finally, the concentration of the test solution can be calculated using the formula:
   
   

   Concentration of test solution (mol L−1)=	l000 × amount of test substance (mol)
   	initial volume of test solution (mL)

   
   Again, the factor of 1000 is used to convert mL to L.