in the last video we learned how to solve problems with a missing concentration today we'll apply the dilution formula to find the missing volume remember the dilution formula is q1 * C1 = Q2 C2 this formula helps us determine the appropriate quantities and concentrations when diluting a solution sometimes we need to find the missing volume this happens when we know the concentrations and one of the volumes but need to find the other volume let's walk through an example you have a 10% stock solution and want to prepare 500 Millers of a 2.5% solution what is the volume of the stock solution first we'll use the formula q1 * C1 = Q2 * C2 in this problem we need to find the volume of stock solution which is q1 we know C1 is 10% because that is the concentration of the stock solution Q2 is 500 Mill and C2 is 2.5% because those are the values of the desired solution plugging in the values we get q1 * 10 = 500 * 2.5 solving for q1 we divide both sides by 10 so q1 = 500 * 2.5 / 10 this is equal to 125 M so the volume of the stock solution needed is 125 M now let's practice with another example suppose we need to prepare 1,00 000 M of a 3% solution from a 15% stock solution what is the volume of the stock solution pause the video and try setting up the problem using the steps we discussed let's walk through it together using the formula q1 * C1 = Q2 * C2 we know C1 concentration of stock solution equal 15% Q2 volume of new solution equals 1000 ml and C2 equal 3% solving for q1 we get q1 = 1000 * 3 / 15 so q1 = 200 M now let's try one more problem on your own suppose we need to prepare 800 milliters of a 4% solution from a 20% stock solution how do we find the volume of the stock solution pause the video and try it yourself now let's review the solution using the formula q1 * C1 = Q2 * C2 we know C1 = 20% Q2 = 800 M and C2 = 4% solving for q1 we get q1 = 800 * 4 / 20 this equals 160 m to summarize understanding how to find missing volumes using the dilution formula ensures accurate preparation of medications now test your knowledge with these questions