Given a 20% w/v solution of chlorhexidine gluconate, what volume is required to make 400 mL of a 2% w/v solution?

Step 1 is to identify the concentration and volume of the desired (diluted) solution and the concentration of the stock (concentrated) solution Desired Concentration (C2): 2% Desired Volume (V2): 400 mL Stock Concentration (C1): 20% Step 2 is to use the dilution formula (C1 × V1 = C2 × V2) to solve for the required volume (V1) Required Volume (V1) = (Desired Concentration ÷ Stock Concentration) × Desired Volume (2 ÷ 20) × 400 2 ÷ 20 = 0.1 0.1 × 400 = 40 Result at this step = 40 mL Step 3 is to round to the nearest whole number 40 = 40 Answer: 40 mL