Question

You have on hand a 14% (w/v) topical antiseptic solution. you receive and order for 1 l of a 1:4000 solution. how much of what is on hand is needed to fill this order?

Answer 1

We are told we have a 14% w/v solution, where w/v is weight/volume. We are asked to prepare 1 L of a 1:4000 solution which can also be written as (1/4000) x 100% = 0.025% w/v solution.

The formula needed here is C1V1 = C2V2 where C1 is the initial concentration, V1 is the initial volume, C2 is the new concentration, and V2 is the new volume.

C1 = 14%
C2 = 0.025 %
V2 = 1 L = 1000 mL
V1 = ?

We must solve for the initial volume V1, which will tell us how much of the initial solution to use.

(14)(V1) = (0.025)(1000 mL)
V1 = 25/14
V1 = 1.8 mL

We will require 1.8 mL of the initial 14% w/v topical antiseptic solution to prepare 1L of a 0.025% w/v solution.