in the previous lesson we learned about concentrations specifically weightto weight concentrations in this lesson we are going explore weight volume concentrations another crucial calculation in Pharmacy practice weight to volume concentrations involve a solid active ingredient like powder combined with a liquid base such as a syrup it is the amount of solute or active ingredient measured in grams present in 100 milliliters of the total mixture the formula to find a weight to volume concentration or percent strength is to divide the weight of the salute which is the substance you are adding to the mixture or active ingredients measured in grams divide this by the volume of the solution which includes both the solute and the base it is mixed in this is measured in milliliters finally multiply this number by 100 to convert it into a percentage this percentage tells you how much of the total mixture is made up of the solute let's look at an example and break down the steps you have 25 gram of an active ingredient in 250 ml of water what is the percent strength in this problem the amount of solute which is the active ingredient is 25 G and the total volume of solution is 250 ml step one establish a ratio using the amount of active ingredient over the total volume G over milliliters for example if you have 25 G of an active ingredient in a 250ml solution the ratio is 25 to 250 or 25 over 250 step two convert this ratio to a decimal by dividing the top value by the bottom value so 25 ID 250 equal .1 step three convert the decimal to a percentage by multiplying by 100 Therefore your 0.1 multiplied by 100 equals 10% now let's practice with an example A 100ml solution has 10 G of an active ingredient what's the concentration remember the steps are one establish the ratio two convert the ratio to a decimal three convert the decimal to a percentage pause the video and try finding the concentration let's walk through it together first first establish the ratio 10 G to 100 ml or 10 over 100 next convert the ratio to a decimal 10 / 100 = 0.1 finally convert the decimal to a percentage 0.1 * 100 = 10% so the concentration is 10% let's try one more a 250ml solution has 5 gr of an active ingredient determine the percent strength pause the video and try it on your own now let's review the solution first establish the ratio 5 G to 250 ml or 5 over 250 next convert the ratio to a decimal 5 / 250 = 0.02 finally convert the decimal to a percentage 0.2 * 100 = 2% so the concentration is 2% in this video we've learned how to calculate weight to volume concentrations and percent strength for compounds these calculations are crucial to accurately preparing medications now it's time to test your knowledge