To determine the concentration of iron III ions in the water sample, the student should follow these steps:1. Prepare a series of standard solutions with known concentrations of iron III ions by diluting the iron III ion standard solution. For example, prepare five standard solutions with concentrations of 1, 2, 4, 6, and 8 ppm parts per million .2. Measure the absorbance of each standard solution using the spectrophotometer at the appropriate wavelength for iron III ions typically around 510 nm . Record the absorbance values.3. Plot a calibration curve by graphing the absorbance values y-axis against the known concentrations of iron III ions x-axis . The graph should be a straight line, and the equation of the line can be determined using linear regression y = mx + b, where m is the slope and b is the y-intercept .4. Measure the absorbance of the unknown water sample using the spectrophotometer at the same wavelength as the standard solutions.5. Use the equation of the calibration curve to calculate the concentration of iron III ions in the water sample. Plug the absorbance value of the unknown sample into the equation and solve for x the concentration .For example, if the equation of the calibration curve is y = 0.5x + 0.1 and the absorbance of the unknown sample is 1.7, the calculation would be:1.7 = 0.5x + 0.11.6 = 0.5xx = 3.2 ppmSo, the concentration of iron III ions in the water sample would be 3.2 ppm.