A chemistry student is asked to determine the concentration of a particular compound in a sample of drinking water. The student collects a 100 mL water sample and adds a known amount of a standard solution containing the compound. After allowing the solution to equilibrate, the student measures the concentration of the compound in the new solution using a spectrophotometer, to be 0.0125 M. Assuming mass balance, calculate the concentration of the compound in the original drinking water sample.

Question

A chemistry student is asked to determine the concentration of a particular compound in a sample of drinking water. The student collects a 100 mL water sample and adds a known amount of a standard solution containing the compound. After allowing the solution to equilibrate, the student measures the concentration of the compound in the new solution using a spectrophotometer, to be 0

Answer 1

To solve this problem, we need to use the concept of mass balance and the formula for dilution:C1V1 = C2V2where C1 is the concentration of the compound in the original drinking water sample, V1 is the volume of the original drinking water sample, C2 is the concentration of the compound in the new solution, and V2 is the volume of the new solution.We are given the following information:- V1 = 100 mL  volume of the original drinking water sample - C2 = 0.0125 M  concentration of the compound in the new solution We also need to know the volume of the standard solution added  V3  and its concentration  C3 . Let's assume the student added V3 mL of a C3 M standard solution. The total volume of the new solution  V2  would be:V2 = V1 + V3Now, we need to consider the mass balance of the compound in the original drinking water sample and the standard solution:C1V1 + C3V3 = C2V2We want to solve for C1, the concentration of the compound in the original drinking water sample:C1 =  C2V2 - C3V3  / V1However, we cannot solve for C1 without knowing the values of V3 and C3. If you provide the volume and concentration of the standard solution added, we can calculate the concentration of the compound in the original drinking water sample.