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Ch 6.4 Other units for solution concentrations | Donald Hirsh | YouTubeToText
YouTube Transcript: Ch 6.4 Other units for solution concentrations
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This content introduces various units used to express the concentration of solutions beyond molarity, including mass percentage, volume percentage, mass/volume percentage, parts per million (ppm), and parts per billion (ppb), and explains their applications.
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
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
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
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
expect
we're generally most interested in the
mass percentages of solutes but it is
also possible to compute the mass
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
the volume percentage is uh defined in a
manner that's very similar so it's just
simply the volume of solute divided by
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
ml
so there's really not a great deal of
difference and this definition is really
so this is just an example of something
you might see at the hospital or with if
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
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
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
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
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
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