Given a 0.5 M stock solution of aqueous NaCl, how much of the stock solution would you need to make a 50 mL sample of 0.25 M aqueous NaCl solution? How much water would you need to add to the NaCl solution?

25 ml of stock

Explanation:

Molarity x Volume of Concentrated Stock = Molarity x Volume of  Diluted Stock

=> Mc x Vc = Md x Vd => (0.5M)(x) = (0.25M)(50 ml)

=> x = Vc = (0.25M x 50 ml) / (0.50M) = 25 ml of stock

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