Lab 1: Determination of Water Hardness

🎯 Objective

To determine the hardness of a given water sample by EDTA complexometric titrimetric method and classify the hardness as temporary or permanent.

📖 Principle / Theory

Water hardness is caused by the presence of dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. EDTA (Ethylenediaminetetraacetic acid) forms stable 1:1 complexes with these metal ions at pH 10. The indicator Eriochrome Black T (EBT) forms wine-red complexes with Ca²⁺/Mg²⁺; at the endpoint, all metal ions are complexed by EDTA and the indicator turns blue.

Reaction: M²⁺ + EDTA⁴⁻ → [M-EDTA]²⁻

Hardness (mg/L as CaCO₃) = (Volume of EDTA × Molarity of EDTA × 100 × 1000) / Volume of water sample

BIS Permissible Limit: Total hardness ≤ 300 mg/L (max 600 mg/L)

🧰 Apparatus Required

Conical flask (250 mL), burette (50 mL), pipette (25 mL), measuring cylinder, beakers, pH meter or buffer solution.

🧪 Chemicals Required

EDTA solution (0.01 M), Eriochrome Black T indicator, NH₄Cl-NH₄OH buffer (pH 10), sample water.

⚗️ Procedure

Pipette out 25 mL of water sample into a 250 mL conical flask.
Add 5 mL of NH₄Cl-NH₄OH buffer solution (pH 10) to the flask.
Add 2–3 drops of Eriochrome Black T (EBT) indicator. The solution turns wine-red.
Fill EDTA solution in the burette. Note the initial reading.
Titrate the solution with EDTA (0.01 M) until the colour changes from wine-red to blue.
Note the final burette reading. Calculate the volume of EDTA consumed (V₁).
Repeat the titration for concordant readings (readings within 0.1 mL).
Calculate total hardness using the formula.

📊 Observations & Calculations

ℹ️

Record all burette readings in the observation table below. Calculate hardness in mg/L as CaCO₃.

Observation	Trial 1	Trial 2	Trial 3
Initial burette reading (mL)	______	______	______
Final burette reading (mL)	______	______	______
Volume of titrant used (mL)	______	______	______
Concordant volume (mL)	______

Calculation:
Volume of titrant (V) = ______ mL
Result = ______ (using appropriate formula)

✅ Result

The total hardness of the given water sample is ______ mg/L as CaCO₃. The water is classified as [soft / slightly hard / moderately hard / hard / very hard] as per BIS standards.