Final answer:
To prepare a 30 ppm solution from a 125 ppm stock solution in a 50 ml volumetric flask, you would need to transfer 12.0 ml of the stock solution and then dilute to the mark.
Step-by-step explanation:
To calculate the volume of a 125 ppm phosphate stock solution needed to prepare a 50.0 ml 30 ppm solution, we apply the dilution formula: C1V1 = C2V2, where C1 and C2 are the concentrations of the stock and final solutions, respectively, and V1 and V2 are the volumes of the stock and final solutions, respectively. In this case, we have C1 = 125 ppm, C2 = 30 ppm, and V2 = 50.0 ml. The formula then becomes (125 ppm) V1 = (30 ppm)(50.0 ml). Solving for V1 gives us V1 = (30 ppm)(50.0 ml)/(125 ppm), which simplifies to V1 = (30/125)(50.0 ml).
After performing the calculation, we find that V1 = 12.0 ml. Therefore, to prepare a 30 ppm solution from a 125 ppm stock solution in a 50.0 ml volumetric flask, you would need to transfer 12.0 ml of the stock solution to the flask and dilute it with solvent up to the 50.0 ml mark.