"Determination of nickel ions Ni²⁺ by using EDTA with the help of back titration"

 

Experiment # 1: Determination of nickel ions Ni²⁺ by using EDTA with the help of back titration

Objective:

This experiment aims to determine the concentration of Ni²⁺ ions in a given solution through a back titration technique using ethylenediaminetetraacetic acid (EDTA) as a complexometric titrant while employing magnesium sulfate as a masking agent.

Introduction:

Back titration is a chemical analysis technique used to determine the concentration of a substance by reacting it with an excess of a known reagent, then titrating the unreacted excess with another reagent of known concentration.

Nickel ions (Ni²⁺) can be quantitatively determined by complexometric titration with EDTA. In this back titration, excess EDTA is added to react with the metal ions, and the unreacted EDTA is then titrated with a standardized solution of a metal ion (usually Zn²⁺) to determine the amount of excess EDTA. The addition of magnesium sulfate helps prevent interference from other metal ions.

Materials Required:

• Nickel sample solution with an unknown concentration
• EDTA solution of known concentration
• Buffer solution (pH ~ 10)
• Standardized Zn²⁺ solution (0.01M ZnSO₄)
• Eriochrome Black T indicator solution

Equipment Required:

• Burette
• Conical flask/Erlenmeyer flask
• Pipette
• pH meter
• Glass stirring rod
• Analytical balance
• Distilled water

Chemical Equation:

Procedure:

1. Prepared 100 mL of 0.01 M of EDTA solution and 100 mL of 0.01 M of ZnSO₄ solution. 

2. Attach the clamp to the stand, and then attach the clamp to hold the burette. Leave enough room for glassware

below the burette. And placed the 250mL beaker, containing 25 mL NiCl₂ below the burette, filled with EDTA

solution

3. Add 2-3 drops of indicator and buffer solution to maintain pH at 10 in the 250 mL beaker and swirl.

4. Open the tap of the burette to add excess EDTA to the beaker, the speed should be dropwise, and the solution will turn from

red to blue. Record the volume of EDTA solution used. 

5. To determine the moles of EDTA combined with Ni²⁺ ion, replace the EDTA solution-filled burette with ZnSO₄

solution-filled burette.

6. And slowly add the ZnSO₄ solution into the beaker till all of the EDTA gets consumed, record the volume of

ZnSO₄ was used in the titration of left EDTA. The solution color gets changed which indicates the end point.

7. Repeat the titration two more times for accuracy.

Calculations

Initial n_EDTA = 25/1000X0.01 = 0.00025 moles

Number of moles of EDTA = 0.00025 moles

Final n_EDTA = 17.6/1000X0.01 = 0.000176 moles

Number of moles of EDTA = 0.000176 moles

Reacted EDTA = Initial n_EDTA - Final n_EDTA

Reacted EDTA = 0.00025 - 0.000176

Reacted EDTA = 0.00008 moles

Number of moles of EDTA= Number of moles of Ni⁺²

                   0.00008            =          0.00008

Molarity of Ni⁺² =  n _Ni+2 / Volume in Liter

Molarity of Ni⁺² = 0.00008/25X1000 =0.0032 mol/L

Safety Precautions:

• Handle chemicals and glassware with care.
• Use appropriate personal protective equipment (lab coat, gloves, safety goggles).
• Work in a well-ventilated laboratory.
• Dispose of chemical waste according to laboratory guidelines.