Question

Household cleaners, such as Windex, typically are dilute solutions of 5-10% w/v NH₃. Propose a set of conditions that will allow you to determine the concentration of ammonia in samples of a household cleaner using HCl as the titrant.

Answer 1

The concentration of ammonia solution, which is a weak base, can be determined by titrating against known concentration of HCl solution used as titrant.

The reaction between ammonia and HCl is

NH₃(aq) + HCl(aq)NH₄Cl(aq)

HCl solution of known concentration is placed in a burette.

A known volume of ammonia solution of unknown concentration is pipetted into an Erlenmeyer flask.

A few drops of an acid-base indicator like methyl orange is added into the Erlenmeyer flask along with ammonia solution. Methyl orange is yellow in alkaline medium and turns reddish in acidic medium.

HCl solution from the burette is run in to Erlenmeyer flask till the colour of the solution changes from yellow to red.

Then by using the following equation,concentration of ammonia solution can be determined

n_HClM_HClV_HCl=n_NH3M_NH3V_NH3

Where,

n_HCl= no. of moles of HCl in balanced chemical equation of equation

M_HCl= Molarity of HCl solution used

V_HCl= Volume of HCl solution added during titration

n_NH3​​​​​​​=no. of moles of NH₃ in balanced chemical equation of equation

​​​​​​​M_NH3= Molarity of ammonia solution

V_NH3 = VOlume of ammonia solution pipetted in to Erlenmeyer flask

In the give case

n_HCl=n_NH3​​​​​​​=1

Therefore,

​​​​​​​M_NH3=(M_HClV_HCl) / V_NH3