Water Hardness Instructor / Prep Information

This experiment requires the following items.

Supplies

• Burettes

• Stir plates + stir bars

• Erlenmeyer flasks or beakers

• Ring stands and burette clamps

• 20-ml pipettes

• 10-ml pipettes

• PE bottles for sample collection (1 L)

• 500 ml PE bottles for samples storage

• Sample storage at 4 C

• Waste container (4 L)

Reagents

• Analytical grade disodium EDTA - to be made to 0.02 N in lab

• 0.02 N Calcium Carbonate (primary standard)

  • Standard calcium solution 0.02 N: Place 1.000 g anhydrous calcium carbonate (primary standard low in metals) in a 500 mL flask. Add, a little at a time, 1 + 1 HCl (6.4.2) until all of the \(\ce{CaCO3}\) has dissolved. Add 200 mL distilled water. Boil for a few minutes to expel \(\ce{CO2}\). Cool. Add a few drops of methyl red indicator (6.4.3) and adjust to intermediate orange color by adding 3N \(\ce{NH4OH}\) (6.4.4) or 1 + 1 HCl (6.4.2) as required. Quantitatively transfer to a 1 liter volumetric flask and dilute to mark with distilled water.

  • Methyl red indicator: Dissolve 0.10 g methyl red in distilled water in a 100 mL volumetric flask and dilute to the mark.

  • Ammonium hydroxide solution, 3 N: Dilute 210 mL of conc. \(\ce{NH4OH}\) to 1-liter with distilled water.

• HCl and \(\ce{HNO3}\) (1:1)

• Water hardness odorless buffer (LabChem)

• Calmagite indicator, 0.1% (LabChem)