Determination of Percentage Purity

When an impure chemical substance is used in titration, only the pure part of that substance takes part in the chemical reaction and is consumed. The impurity will not react. 

Example 1.2.1:

A is 0.100 mol dm^-3 solution of HNO₃. 
B is a 5.00 g mixture of Na₂CO₃ and NaCl in 500 cm³ of solution.

Put A into a burette and titrate it against 25 cm³ portions of B using methyl orange as an indicator. Tabulate your burette readings and determine the average volume of A used. From your result and the information provided, calculate the

i. Concentration of Na₂CO₃ in mol dm^-3
ii. Concentration of Na₂CO₃ in g dm^-3
iii. Percentage purity

The equation for the reaction is: 

2HNO_3(aq) + Na₂CO_3(aq) → 2NaNO_3(aq) + H₂O_(l) + CO_2(g)

Results and Calculations

• Indicator used – methyl orange
• Volume of pipette – 25 cm³