Analysis of a spring water

• Standard laboratory equipment, in particular: graduated burette, glassware, pipette filler.
• A sand-bath hot plate
• Concentrated sulfuric acid at ½ dilution
• Saturated solution of monosodium carbonate NaHCO₃
• Titrated solution of potassium permanganate KMNO₄ at 0.0025 mol/L (i.e. N/80)
• Iron and ammonium sulfate solution (FeSO₄(NH₄)₂SO₄, 6H₂O) (Mohr’s salt; M = 392.14 g/mol) at about 5 g/L (slightly sulfuric) – This solution is difficult to keep- it must be compared to the potassium permanganate solution every day.

Comparison of the oxidizing and reducing solutions:

In 200 mL of distilled water, add 5 mL of sulfuric acid, 20 mL of KMNO₄ at 0.0025 mol/L, then 20 mL of Mohr salt.
Titrate the excess of Mohr salt with the solution of KMNO₄ at 0.0025 mol/L, until a pink color appears (persistent for 1 min).
This excess of Mohr salt must exist and remain small, corresponding to maximum 0.5 mL of potassium permanganate.
Let V₀ be the volume (mL) of potassium permanganate solution used to titrate this excess of Mohr salt.