Name of Experiment: Preparation of Hardness In Water

Apparatus: 1. 250 ml conical flask 2. 100 ml pipettes and pipette filler 3. 50 ml burette 4. 10 ml measuring cylinder 5. Clamp 6. Retort stand
Reagents: 1. Ammonium hydroxide/ammonium chloride ( NH4OH/NH4CL) buffer at pH 10 2. M ethylenediamminetetraacetic acid (EDTA) [Atomic weight: 372.74g] 3.Eriochrome Black T indicator 4. Water sample (e.g tap,river or lake water)

Procedure: 1. 100ml of tap water was pipette into a 250 ml conical flask.
2. 5ml of NH4Cl/NH4OH buffer was added to the conical flask then 4 drops of Eriochrome Black T indicator was added.
3. The solution was titrated with 0.01 M EDTA until the indicator color changed from red to pure blue
4. The titration was repeated thrice to achieve consistent results.

Calculations and result
1 ml 0.01 M EDTA = 1 MG CaCO3
After three titration the result obtained were 6.8, 6.6 and 6.7.
We know,
1 ml = 1mg CaCo3
6.8 = 6.8 mg CaCo3
100 ml – 6.8 mg CaCo3
1ml – 6.8/100ml
1000 – 68mg/l of hardness.

Precaution : Conical flask should me moved back and fro till the color change is sharp from red to blue.

Comments: Hardness is defined as the sum of the concentration of Ca2+ and Mg2+, traditionally expressed as milligrams per liter of water of calcium carbonate.
The experiment helped us determined the level of hardness through break down of calcium carbonate and presence of Ca2+.