Exercise 1: Calculation of the sampling volumes for the calibration

The aim is to carry out an external calibration in order to measure the concentration of a dye in wastewater treated by chemical oxidation, so as to assess the residual amount of dye remaining in the treated water – this will ultimately allow us to estimate the effectiveness of the oxidation treatment in degrading this dye.

In order to do this, a dye stock solution must be prepared beforehand; the standard solutions of the calibration will be prepared from this stock solution.

The dye in question (Acid Black 1) is a toxic diazo dye with a molar mass of 616.5 g/mol – its formula is given below:

Chemical formula of acid black 1

A stock solution of this dye must be prepared at 2.9 x10-4 mol/L: a 1 liter flask is available for this.

Question 1: What is the mass (in mg) of dye to be weighed in order to obtain this stock solution?

Answer: 178.8 mg
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50 mL volumetric flasks are available for preparing standard solutions with the following concentrations: 0.29 x 10-5 mol/L – 0.7 x 10-5 mol/L – 1.5 x 10-5 mol/L – 2.9 x 10-5 mol/L – 5.8 x 10-5 mol/L.

Question 2: What volumes (in mL) of stock solution need to be sampled in order to prepare these standard solutions?
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