To determine the concentration of zinc from zinc chloride, you can employ various analytical techniques. One common method is titration, specifically known as complexometric titration using a chelating agent called EDTA (ethylenediaminetetraacetic acid). Here's a general procedure for determining the zinc concentration using EDTA titration:
Materials and Equipment:
- Zinc chloride solution (unknown concentration)
- EDTA solution (standardized)
- Eriochrome Black T indicator solution
- Buffer solution (pH-adjusted to a suitable range, usually around pH 10)
- Distilled water
- Burette
- Erlenmeyer flask
- Pipettes and pipette bulb
- Magnetic stirrer (optional)
- Graduated cylinder
- Analytical balance
Procedure:
Preparation: a. Standardize the EDTA solution by titrating it against a known concentration of a zinc standard solution. b. Prepare the buffer solution and adjust its pH to the desired range using a suitable acid or base.
Sample Preparation: a. Accurately measure a known volume of the zinc chloride solution using a pipette and transfer it into an Erlenmeyer flask. b. If necessary, dilute the sample with distilled water to achieve a suitable concentration range for the titration.
Titration: a. Add a few drops of the Eriochrome Black T indicator solution to the flask containing the zinc chloride sample. The indicator will form a colored complex with the zinc ions. b. Place the flask on a magnetic stirrer or use a glass rod to mix the solution gently. c. Slowly add the standardized EDTA solution from a burette into the flask while stirring the solution continuously. d. The EDTA forms a more stable complex with zinc ions, displacing the indicator. The indicator will change color from wine-red (indicating excess zinc ions) to a blue or violet endpoint (indicating all zinc ions have complexed with EDTA). e. Take note of the volume of the EDTA solution added.
Blank Determination: a. Perform a blank determination by repeating steps 3a to 3d with the same amount of distilled water and indicator solution instead of the zinc chloride sample. b. This blank determination accounts for any titration of impurities or background color changes.
Calculation: a. Calculate the concentration of zinc in the original sample using the volume of EDTA solution used in the titration, the molarity of the EDTA solution, and the dilution factor if the sample was diluted.
It's important to note that the specific procedure, including the volumes and concentrations used, may vary depending on the equipment and reagents available and the desired accuracy of the analysis. Always refer to the appropriate literature or consult a qualified chemist for detailed instructions and precautions.