Analytical Chemistry

Question

A 100.0 mL sample of drinking water was treated with ammonia buffer and after the addition of the Eriochrome Black T indicator, required 18.0 mL of 0.00559 M EDTA for titration.

(a) Identify the role of ammonia buffer in the analysis.

(b) Identify the indicator and endpoint color.

(c) Calculate the total hardness of the water sample as ppm CaCO3

Answer 1

This is an example of complexometric titrations; once you read the passage, you will need to write a net ionic (chemical) equation.

a. You need to understand the definition of buffers or buffered solution and their role in a chemical reaction. You may review basics in chemical equilibrium, acid/base theories and aqueous ionic equilibrium.

b. besides EDTA, the ligand, what is the other reactant or the ion in the drink water? You may get hints from Part C.

Regarding how those indicators work, you need to understand what chemical species are in the reaction mixture before the titration starts and after it completes, then the colors could be either Blue/Red or Red/Blue.

c. Complete the calculation of this chemical equation (stoichiometry) to determine the concentration of THE metal cation, then convert the concentration to mass of CaCO3 (mg) per liter of drinking water.

Consider a tutor and you may seek help on a regular basis. Good luck!