To calculate the original concentration of phosphate in the lake water sample, the dilution equation M1V1 = M2V2 is used, but the necessary final volume and concentration values after dilution are missing, making it impossible to determine the original concentration without additional information.
To find the concentration of phosphate in the original lake water sample after dilution, we use the dilution equation, which is M1V1 = M2V2. In this equation, M1 and V1 represent the molarity and volume of the original solution, while M2 and V2 represent the molarity and volume after dilution. Unfortunately, the question does not provide the final volume (V2) or the final concentration (M2) to which the 25.0 mL of lake water was diluted. To perform the calculation, these values are necessary. Without them, we cannot determine the original concentration of phosphate in the lake water.