in section 6.4 we're going to talk about other units that are used to measure the concentration of solutions or to describe the concentration of solutions so your learning objectives for this section are to be able to define the concentration units of mass percentage volume percentage mass volume percentage parts per million and parts per billion and then be able to perform computations related relating to Solutions concentration and its components volumes and our masses using these units so while chemists often use units of molarity to describe concentration there are other units of concentration that are commonly used in other fields or in different applications so for instance mass percent is often used to describe Solutions of things that you might find in the store like your grocery store or your hardware store a volume percent is sometimes used mass volume percent is a very common unit of concentration or measure of concentration for medicine and finally parts per million or parts per billion is often used to describe the concentration of toxins that are found in the environment so let's start with mass percentage uh the mass percentage of a solution component is defined as a ratio of the component's mass to the solutions Mass expressed as a percentage so very straightforward mass percentage of a solute is the mass of that component divided by the mass of the solution times a hundred it's exactly what you'd expect we're generally most interested in the mass percentages of solutes but it is also possible to compute the mass percentage of solvent so for example liquid bleach is an aqueous aqueous solution of a sodium hypochlorite of sorry of sodium hypochlorite this brand has a concentration of 7.4 percent sodium hypochlorite by mass okay so massive sodium hypochlorite in this case to the mass of this solvent which in this case is water um just a short note here uh don't be confused by the fact that it's Representatives ocl this is still hypochlorite so we usually write it clo um but here they chose to wrote it write it as ocl the volume percentage is uh defined in a manner that's very similar so it's just simply the volume of solute divided by the volume of solution times a hundred a mass volume percent is a ratio of a solute's mass to the solutions volume expressed as a percentage so the specific units for solute mass and solution volume may vary depending on the type of solution that you're talking about but as an example the saline solutions that are used to prepare intravenous fluids at the hospital have a concentration of 0.9 grams of sodium chloride per 100 ml of solution or they're called a 0.9 percent mass per volume solution one of the reasons that this is you is that this mass per unit volume Solutions uses typically used with water and it's typically used because it's also very close to the mass percentage right because the density of a dilute solution of water is very close to one gram per ml so there's really not a great deal of difference and this definition is really one of convenience that's used so this is just an example of something you might see at the hospital or with if EMS comes to treat somebody if you have very low solute concentrations then those are often expressed using appropriately small units such as parts per million or parts per billion and the mass-based definitions of parts per million parts per billion are simply the mass of the solute divided by the mass of solution times 10 to the 6 right because 10 to the 6 represents a million uh parts per billion is again simply mass of solute divided by a mass of solution but this time multiplied by a billion or 10 to the ninth so just as an example of this parts per million and parts per billion this is a report that I got in 2019 from Trenton Waterworks that's where our water comes from and um what they were one of the important things they were reporting was that they had exceeded their own limits for lead in the water at several locations so let me just walk you through this so here's the um here's the metal that they're following which is lead they're also following copper you can see that below but I'm going to focus on lead and the units that they're using are parts per billion their action limit is 15 parts per billion so um uh if 90 of the samples are not less than 15 parts per billion then they have to take action that's considered a violation and you can see that with the red yes or Y symbol here so um and then mclg stands for maximum let me see it's basically the maximum level that's thought to be safe and for lead there is really no maximum level above zero and that's because Mac uh lead is a cumulative um toxin that can accumulate in the body over over many years um one thing also that they note is that um the typically the source of this is corrosion of household plumbing and so you may have heard about how Newark a few years back had a massive campaign to replace the plumbing lines going from the main water line into the houses and Trenton Waterworks has also initiated um a pro uh a program like that also this is just an example where you would see parts per billion or parts per million in your everyday life