Colorimetric analysis of a solution of unknown concentration
Goal: to determine the unknown concentration of a transition metal in solution by interpolating a
calibration curve.
Relevant skills:
Tool 1: Use and apply colorimetry
Tool 1: Prepare a standard solution
Tool 1: Carry out dilutions
Tool 3: Interpolate graphs
Tool 3: Draw and interpret uncertainty bars
Inquiry 1: Calibrate measuring apparatus, including sensors
Inquiry 3: Discuss the impact of uncertainties on the conclusions
Inquiry 1: Formulate research questions
Transition metal solutions: Copper sulfate, potassium permanganate
Method:
1. Prepare a standard solution of the ion you will be analysing, and perform a serial dilution to
obtain five solutions of different concentrations.
2. Depending on the colour of the solution, determine a suitable wavelength of incident light.
3. Calibrate the colorimeter
4. Determine the absorbances of the five standard solutions
5. Plot a calibration curve that shows absorbance vs. concentration
6. Check for errors by verifying that your line of best fit goes through the origin
7. Propagate uncertainties and include error bars on your graph. Draw lines to determine the
maximum and minimum gradients.
8. Obtain a small sample of the solution of unknown concentration. Determine the absorbance of
the analysed solution
9. Use your calibration curve to determine the concentration of the analysed ion in the solution
Developing a research question
Brainstorm possible research questions that could involve using this analytical technique.
Title:
Title: