we know how to calculate mass percentage and this can be useful when we want to make a solution using a solute that is solid because we can just measure some mass of solute and we won't have to do any calculations involving moles but we can also generate Solutions according to volume percentage volume percentage refers to the percentage of a solution that is represented by a particular component by vol volume this is useful if we are mixing liquids because it can often be more practical to measure the volume of a liquid than its mass and if we need to discuss the mass of any component we can always use the density to go from volume to mass for example rubbing alcohol that is sold over the counter is called isopropanol and is typically around 70% alcohol by volume with the rest being water in a typical 300 155 mL bottle of rubbing alcohol what mass of isopropanol is present well let's take our total volume and first we must multiply by 0.7 because only 70% of the solution is alcohol so there are only 70 milliliters of alcohol for every 100 milliliters of solution that will give us the volume of alcohol that is present in the bottle which is 248.50 milliliters now to convert this volume into a mass we will need the density which is 0.785 G per milliliter we can simply multiply our volume by the density to get the mass of alcohol in the bottle we should get around 195 gram of isopropanol and that will give us our 70% alcohol by volume let's say we encounter another brand of rubbing alcohol and they advertise that there are two 25 G of isopropanol in each 400ml bottle is this more or less concentrated than the first bottle well in sticking with volume percentage let's convert this Mass into volume by using the density we should get around 274 milliliters 274 mL of alcohol out of a total 400 milliliters makes this solution about 68.5% alcohol by volume so it is actually slightly less concentrated than the first bottle and now we know about volume percentage