When working with dilutions we usually use this formula:
Vi * Mi = Vf * Mf
Where:
Vi = initial volume or the volume before the dilution
Mi = initial molarity or the molarity before the dilution
Vf = final volume or the volume after the dilution
Mf = final molarity or the molarity after the dilution
According to the problem we have:
Vi = ? mL
Mi = 11.65 M
Vf = 500 mL
Mf = 3.00 M
Since the initial volume is our unknown we will solve the formula for Vi:
Vi = Vf * Mf / Mi
Replacing:
Vi = 500 mL * 3.00 M / 11.65 M
Vi = 129 mL
We have to take 129 mL of the solution.
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