You need to prepare 100 mL of a 10 mg/mL solution. Stock concentration is 50 mg/mL. How many mL of stock are required, and what is the final total volume?

You need to prepare 100 mL of a 10 mg/mL solution. Stock concentration is 50 mg/mL. How many mL of stock are required, and what is the final total volume?

• A. 10 mL stock; final volume 100 mL
• B. 25 mL stock; final volume 125 mL
• C. 20 mL stock; final volume 100 mL
• D. 30 mL stock; final volume 130 mL

Answer: (C)

To get 100 mL of a 10 mg/mL solution, you need a total of 1000 mg of solute (100 mL × 10 mg/mL). The stock solution has 50 mg of solute per mL, so the volume of stock needed is 1000 mg ÷ 50 mg/mL = 20 mL. After drawing 20 mL of stock, you add diluent to reach the final volume of 100 mL (80 mL of diluent). This way, the final solution is 100 mL at 10 mg/mL.

To get 100 mL of a 10 mg/mL solution, you need a total of 1000 mg of solute (100 mL × 10 mg/mL). The stock solution has 50 mg of solute per mL, so the volume of stock needed is 1000 mg ÷ 50 mg/mL = 20 mL. After drawing 20 mL of stock, you add diluent to reach the final volume of 100 mL (80 mL of diluent). This way, the final solution is 100 mL at 10 mg/mL.