Question

Describe how to analyze a solution of NaI by using the Volhard

titration.

Short answer

Complex shows us the end point of the titration.

Step-by-step solution

Volhard Method

The Volhard method is an indirect or back titration method in which an excess of a standard solution of silver nitrate is added to a chloride containing sample solution. The excess silver is then back titrated using a standardized solution of potassium or ammonium thiocyanate with ferric ion as an indicator.

Explanation of how shows us the end point of the titration 

We use the Volhard method to analyze certain anions that react with Ag⁺ cation, for example iodide in NaI. First we add AgNO₃ to the NaI solution and solid AgI forms:

${\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)+{\mathrm{l}}^{-}\left(\mathrm{aq}\right)𝆏\mathrm{Agl}\left(\mathrm{s}\right)$

The solution is then filtered and washed with HNO₃ to collect Ag⁺.

Then Fe(NO₃)₃ is added to put free Fe³⁺ in the solution. KSCN is added to solid AgSCN forms:

${\mathrm{Ag}}^{+}\left(\mathrm{aq}\right)+{\mathrm{SCN}}^{-}\left(\mathrm{aq}\right)𝆏\mathrm{AgSCN}\left(\mathrm{s}\right)$

At the end, when all Ag⁺ reacts, SCN^- reacts with Fe³⁺ and forms a red complex and that complex shows us the end point of the titration.

Hence, the final answer is that complex shows us the end point of the titration.