Colorimetry is a technique used to determine the concentration of a specific substance in a sample by measuring the absorbance of light at a particular wavelength. The underlying principle behind colorimetry is the Beer-Lambert Law, which states that the absorbance of light by a solution is directly proportional to the concentration of the absorbing substance and the path length of the light through the solution.Here is a stepwise procedure to determine the concentration of a specific substance in a sample using colorimetry:1. Preparation of standard solutions: Prepare a series of standard solutions with known concentrations of the substance of interest. These solutions will be used to create a calibration curve.2. Selection of wavelength: Choose an appropriate wavelength at which the substance of interest absorbs light. This can be done using a spectrophotometer or by consulting the literature for the substance's absorption spectrum.3. Calibration curve: Measure the absorbance of each standard solution at the selected wavelength using a colorimeter or spectrophotometer. Plot the absorbance values against the known concentrations of the standard solutions to create a calibration curve. The calibration curve should be a straight line that passes through the origin, indicating a linear relationship between absorbance and concentration.4. Sample preparation: Dilute the sample, if necessary, so that its concentration falls within the range of the calibration curve. Make sure to record the dilution factor for later calculations.5. Measurement of sample absorbance: Measure the absorbance of the diluted sample at the selected wavelength using the colorimeter or spectrophotometer.6. Determination of concentration: Use the calibration curve to determine the concentration of the substance in the diluted sample. Locate the measured absorbance value on the y-axis of the calibration curve, and find the corresponding concentration on the x-axis.7. Correction for dilution: If the sample was diluted in step 4, multiply the determined concentration by the dilution factor to obtain the concentration of the substance in the original, undiluted sample.By following these steps, you can accurately determine the concentration of a specific substance in a sample using colorimetry. The key to this method's success is the establishment of a reliable calibration curve and the careful selection of an appropriate wavelength for absorbance measurements.