Final answer:
To make 15.0mL of a .500M Na2CO3 solution from 10.0mL of 1.25M solution, use the formula M1V1 = M2V2 to calculate that 5.0mL of water is needed to dilute the existing solution.
Step-by-step explanation:
To prepare 15.0mL of a .500M Na2CO3 solution using a more concentrated 10.0mL of a 1.25M solution, one can employ the dilution formula M1V1 = M2V2, where M is molarity and V is volume. In this case, we want to find out how much water (V_water) we need to add to the existing 10.0mL of 1.25M Na2CO3 to obtain a final volume (V2) of 15.0mL of a .500M solution. Plugging in the known values into the formula gives us (1.25M)(10.0mL) = (.500M)(15.0mL). Solving for V_water, we find that we need to add 5.0mL of water to the existing solution.
Dilution calculations are commonly used in various chemistry experiments to obtain solutions of desired concentrations from more concentrated stock solutions. By understanding the relationship between the initial and final concentrations and volumes, one can accurately prepare solutions with specified molarity.