1. Convert mM to M (molarity):

* 50 mM = 0.05 M (since 1 M = 1000 mM)

2. Calculate the moles of NaCl needed:

* Molarity (M) = moles of solute / liters of solution

* 0.05 M = moles of NaCl / 0.5 L

* moles of NaCl = 0.05 M * 0.5 L = 0.025 moles

3. Calculate the mass of NaCl needed:

* mass = moles * molecular weight

* mass = 0.025 moles * 58.5 g/mole = 1.4625 g

Therefore, you would dissolve 1.4625 grams of NaCl in water to make a 50 mM solution with a final volume of 500 ml.