Determination of water hardness

Determination of water hardness

Introduction :

When water contain Ca²⁺, Mg²⁺, and HCO^3– ions in high amount or number than we called it hard water.

Purposes :

1. To determine the concentrations of Ca2+(aq) and Mg2+(aq) ions in a commercial

sample of bottled mineral water.

2. To compare experimental results with the concentrations of the metal ions claimed

by the manufacturer.

Materials :

1.      Erlenmeyer flask.

2.      Buffer Solution.

3.      Indicator solution.

4.      0.01 M EDTA.

5.      Dropper.

Testing Procedure :

1.      Use a graduated cylinder to measure 50 mL of your water sample into a 250 mL Erlenmeyer flask.

2.      Add 1 ml of Hardness 1 Buffer Solution to the Erlenmeyer flask using the 1 ml

calibrated dropper or 4/5 drops by any dropper. Than mix it.

3.      Add 2/3 drops Indicator solution in Flask. Than mix it.

Titrate

4.      Slowly add 0.01 M EDTA titrant to the sample in the Erlenmeyer flask start with

1 ml dropper.  Mix the sample after each addition of titrant.

5.      Near the equivalence point, the red color will start to fade, and become more violet (just between of red and blue). You should stop the adding EDTA at the time. Reading the EDTA amounts.

Note: The reaction at the equivalence point is very slow (~1 second), so take your time.

Calculations :

Ø  30 * ml of EDTA (For 50 ml water)

Ø  75 * ml of EDTA (For 20 ml water)

Grade :

                          • Soft: 0-30

                          • Moderately soft: 30-60

                          • Moderately hard: 60-120

                          • Hard: 120-180

                          • Very hard: >180