Engineering Chemistry Lab Experiments

Estimation of total hardness of water by complexometric method using EDTA

Dec 31 2023

Aim

To estimate the total hardness, permanent hardness and temporary hardness of water by using standard solution of EDTA

Apparatus Required:

Burette, pipette, Conical flask, Beakers, Standard flask, Burette stand and funnel etc.,

Chemicals Required :

Magnesium sulphate, Buffer, Disodium salt of EDTA, Eriochrome black-T or Solochrome balck -T etc.

Principle :

Hard water which contains Ca ²⁺ and Mg ²⁺ ions which forms wine red color complex with the indicator

Ca ²⁺ or Mg ²⁺ + EBT ———> C ^a-EBT (or) M ^g-EBT (Wine red colour complex)

EDTA forms a colour less complex with the metal ions (C _a ²⁺ and M ^g²⁺)

(Wine red colour complex) (Colorless stable complex) (Blue)

When free ions are not available, EDTA extracts the metal from (ion) metal ion indicator complex, there by releasing the free indicator.

Procedure:

Step-I

Preparation of Standard Solution of MgSO4: Weigh the approx 0.25gm of MgSO4 and transfer into 100ml standard flask through the funnel and dissolve in minimum quantity of distilled water. Make up the solution up to the mark with distilled water and shake the flask well for uniform concentration then calculate the Molarity of MgSO4

Molecular Weight of MgSO4 = 246.48gm

Molarity of MgSO4=0.01M

Step-II

Standardization of EDTA solution: Pipette out 20ml of MgSO4 solution into a clean conical flask. Add 2ml of buffer solution and add 2 to 3 drops of EBT indicator and it gets wine red color solution Take EDTA solution in a burette after titrate with EDTA solution till wine red color changes to blue color. Note the burette reading and repeat the titration to get concurrent values.

S. No	Volume of MgSO4 in ml	Burette Reading (ml)/Initial/Final	Volume of EDTA consumed (ml)
1	20
2	20
3	20

M ₁ = MgSO4 molarity M ₂= EDTA molarity

V ₁ = volume of MgSO4 V ₂= Volume of EDTA consumed

M ₁ V ₁ = M ₂ V ₂

M ₂ = M ₁V ₁/V ₂

Step-III

Standardization of Permanent Hardness of Water :Pipette out 100ml of hard water sample into a beaker containing 250ml and boil the water till volume reduces to 50ml (all the bicarbonates of Ca ₂₊, Mg ₂₊decomposes toCaCO3and Mg(OH) ₂ respectively). Cool the solution and filter the water into beaker then pipette out 20ml of this cool water sample in to 250ml conical flask add 2ml of buffer solution and 2-3 drops of EBT indicator. Titrate the wine red color solution with EDTA taken in the burette, till a blue colored solution end point is obtained. Repeat the titration to get concurrent values.

S. No	Volume of Hard water in (ml)	Burette Reading (ml)/Initial/Final	Volume of EDTA consumed (ml)
1	20
2	20
3	20

M ₃ = molarity of hard water M ₂= EDTA molarity

V ₃ = volume of hard water V ₂ ¹ = Volume of EDTA consumed

M ₃ V ₃ = M ₂ V ₂ ¹

M ₃ = M ₂V ₂ ¹/V₃

Total hardness= M ₃X100X1000 =------------PPM

Step-IV

Standardization of Permanent Hardness of Water : Pipette out 100ml of hard water sample into a beaker containing 250ml and boil the water till volume reduces to 50ml (all the bicarbonates of Ca ₂₊, Mg ₂₊ decomposes to CaCO3and Mg(OH) ₂ respectively). Cool the solution and filter the water into beaker then pipette out 20ml of this cool water sample in to 250ml conical flask add 2ml of buffer solution and 2-3 drops of EBT indicator. Titrate the wine red color solution with EDTA taken in the burette, till a blue colored solution end point is obtained. Repeat the titration to get concurrent values.