0:03 in section 6.4 we're going to talk about
0:07 other units that are used to measure the
0:08 concentration of solutions or to
0:11 describe the concentration of solutions
0:13 so your learning objectives for this
0:16 section are to be able to define the
0:18 concentration units of mass percentage
0:22 volume percentage mass volume percentage
0:25 parts per million and parts per billion
0:27 and then be able to perform computations
0:29 related relating to Solutions
0:32 concentration and its components volumes
0:39 so while chemists often use units of
0:41 molarity to describe concentration there
0:43 are other units of concentration that
0:45 are commonly used in other fields or in
0:47 different applications
0:50 so for instance mass percent is often
0:52 used to describe Solutions of things
0:54 that you might find in the store like
0:55 your grocery store or your hardware store
0:56 store
1:00 a volume percent is sometimes used mass
1:03 volume percent is a very common unit of
1:04 concentration or measure of
1:07 concentration for medicine
1:11 and finally parts per million or parts
1:14 per billion is often used to describe
1:16 the concentration of toxins that are
1:22 so let's start with mass percentage uh
1:23 the mass percentage of a solution
1:26 component is defined as a ratio of the
1:29 component's mass to the solutions Mass
1:31 expressed as a percentage so very
1:34 straightforward mass percentage of a
1:37 solute is the mass of that component
1:39 divided by the mass of the solution
1:42 times a hundred it's exactly what you'd expect
1:43 expect
1:45 we're generally most interested in the
1:48 mass percentages of solutes but it is
1:49 also possible to compute the mass
1:55 so for example liquid bleach is an
1:57 aqueous aqueous solution of a sodium
2:00 hypochlorite of sorry of sodium
2:03 hypochlorite this brand has a
2:06 concentration of 7.4 percent sodium
2:10 hypochlorite by mass okay so massive
2:13 sodium hypochlorite in this case to the
2:16 mass of this solvent which in this case
2:18 is water
2:20 um just a short note here uh don't be
2:22 confused by the fact that it's
2:24 Representatives ocl this is still
2:27 hypochlorite so we usually write it clo
2:29 um but here they chose to wrote it write
2:37 the volume percentage is uh defined in a
2:39 manner that's very similar so it's just
2:42 simply the volume of solute divided by
2:49 a mass volume percent is a ratio of a
2:52 solute's mass to the solutions volume
2:55 expressed as a percentage
2:59 so the specific units for solute mass
3:01 and solution volume may vary depending
3:03 on the type of solution that you're
3:04 talking about
3:08 but as an example the saline solutions
3:10 that are used to prepare intravenous
3:12 fluids at the hospital have a
3:15 concentration of 0.9 grams of sodium
3:19 chloride per 100 ml of solution or
3:22 they're called a 0.9 percent mass per
3:24 volume solution
3:26 one of the reasons that this is you is
3:28 that this mass per unit volume Solutions
3:31 uses typically used with water and it's
3:34 typically used because it's also very
3:36 close to the mass percentage right
3:38 because the density of a dilute solution
3:40 of water is very close to one gram per ml
3:41 ml
3:43 so there's really not a great deal of
3:45 difference and this definition is really
3:53 so this is just an example of something
3:57 you might see at the hospital or with if
4:04 if you have very low solute
4:06 concentrations then those are often
4:08 expressed using appropriately small
4:10 units such as parts per million or parts
4:12 per billion
4:14 and the mass-based definitions of parts
4:16 per million parts per billion are simply
4:19 the mass of the solute divided by the
4:22 mass of solution times 10 to the 6 right
4:25 because 10 to the 6 represents a million
4:28 uh parts per billion is again simply
4:30 mass of solute divided by a mass of
4:33 solution but this time multiplied by a
4:40 so just as an example of this parts per
4:42 million and parts per billion this is a
4:45 report that I got in 2019 from Trenton
4:47 Waterworks that's where our water comes
4:49 from and
4:51 um what they were one of the important
4:53 things they were reporting was that they
4:55 had exceeded their own
4:58 limits for lead in the water at several
5:00 locations so let me just walk you
5:04 through this so here's the um here's the
5:06 metal that they're following which is
5:08 lead they're also following copper you
5:09 can see that below but I'm going to
5:12 focus on lead and the units that they're
5:21 their action limit is 15 parts per
5:22 billion so
5:27 um uh if 90 of the samples are not less
5:30 than 15 parts per billion then they have
5:32 to take action that's considered a
5:35 violation and you can see that with the
5:38 red yes or Y symbol here so
5:39 so
5:44 um and then mclg stands for maximum let
5:45 me see
5:48 it's basically the maximum level that's
5:51 thought to be safe and for lead there is
5:55 really no maximum level above zero and
5:57 that's because Mac uh lead is a cumulative
5:58 cumulative
6:01 um toxin that can accumulate in the body
6:04 over over many years
6:07 um one thing also that they note is that
6:10 um the typically the source of this is
6:13 corrosion of household plumbing and so
6:16 you may have heard about how Newark a
6:19 few years back had a massive
6:23 campaign to replace the plumbing lines
6:26 going from the main water line into the
6:31 houses and Trenton Waterworks
6:34 has also initiated
6:37 um a pro uh a program like that also
6:40 this is just an example where you would
6:42 see parts per billion or parts per
