hello and welcome to a video about solubility and saturation so what we're gonna look at today is
solubility and the solubility curve saturation three equilibrium unsaturated solution for
solubility curves revisited five saturation vs. super saturation and six gas solubility and its
significance water is a solvent and water is usually the solvent that people are interested
in because of water's ability to dissolve a huge variety of compounds and that includes all of
the reactants that react in living organisms to produce very valuable products a solute is
the compound that gets dissolved a salt crystal large enough to see with your own eyes would have
greater than 10 to the 22 ions in it so that is what this is representing and when we put it in
the water it splits apart they dissociate and here we have a solution composed of water and
the dissolved particles solubility is the maximum amount of solute that can dissolve and we will go
into much more detail shortly solubility curves give us maximum amounts that can dissolve and
we will explore that intimately starting now let's just look at one of these curves for now
is that of sodium acetate and let's see what sort of information this curve gives us so we call this
a solubility curve or the solubility line and that shows the maximum solute that can be dissolved for
100 grams of h2o which is what we put on the y-axis but that maximum is per some specific
temperature so at any given temperature you have a specific amount that you can dissolve and that
amount increases as the temperature increases so for example if we have a maximum amount dissolved
at 40 degrees Celsius the amount that can dissolve was simply read on the y-axis so 93 grams is the
solubility of this substance at 40 degrees Celsius 93 grams is the maximum that can be dissolved at
40 degrees Celsius the term saturation tells us that the maximum amount of solute is dissolved
so in these conditions 93 grams saturates 100 grams of water at 40 degrees Celsius the term
solubility however is more specific it is quantitative solubility is the maximum mass
of solute that can be dissolved per given mass of water at a given temperature so any condition
of concentration and temperature below the line is considered unsaturated less than the maximum
solute is dissolved any condition of concentration and temperature above the line is saturated so
what's the difference between that and being on the line let's take a look so let's say you're
at room temperature and unsaturated we're on the graph would you be well about 22 or 23 degrees is
room temperature and we're gonna be below the solubility line so we'll put our point right
there that's room temperature and unsaturated now we're going to assume that adding this amount will
results in maximum dissolved solute we're on the graph would we be what do you think let's take a
look so here we are now if we drop this in and it dissolves we are now at the maximum amount that
can be dissolved so we are now on the solubility curve we are both at solubility and saturation
so we can use the graph to see the amount added to saturate the solution what's going to happen
if we add even more solute let's take a look it does that appear to dissolve and they see the
word appear very specifically we will explore that very soon so what you would see visually
is undissolved solute sitting at the bottom and as we know we can't actually see those individual
particles that are dissolved and so the solution looks clear and so the graph tells us the amount
that remains as a solid but what's really going on here let's go back to is the solubility curve and
drop that same amount in again so what happens is that actually does dissolve the particles in that
solid continually go into solution while particles in solution continually join the crystal it keeps
going back and forth but the amount the total amount of solid remains virtually constant so
on a macro scale we actually don't see any change in the salad that is there so if you
see salad sitting at the bottom of a solution then the solution is saturated and it is in
equilibrium with the salad what does that mean the amount of solid that dissolves into solution
is equal to the amount of dissolved particles that join the crystal that is our equilibrium
so the difference between being saturated on the solubility line is that there's no
equilibrium there's no visible solid everything is dissolved but if you go above the solubility
line you're still saturated but now you have solid that is in equilibrium with the solution
solid particle is continually dissolving while dissolved particles continually recrystallize
so let's look at something interesting solubility is dependent on temperature let's see what happens
to that salad as we heat up the solution yes it dissolves it breaks apart let's watch it
again closely right as the blue dot crosses the solubility line the last of the particles break
up so we are now unsaturated we have heated it up where we can actually add more solute
to this solvent and have them dissolve what's really interesting about this that Brown area
the condition of concentration and temperature above the solubility line can also be something
called supersaturated it can be supersaturated under specific conditions we just cool it down
carefully and do not provide a small crystal face for the dissolved particles to start crystallizing
on to the particles will stay in solution unless they have a crystalline face to join and become
solid so here's an unsaturated solution of sodium acetate and the blue dad tells us where we are on
the solubility graph and then this was cooled down but now the solute above maximum remains as all so
now we're looking at a supersaturated solution it looks the same we don't see any difference
so what we're gonna do now is drop in a couple of seed crystals in other words tiny crystals
that provide a little face for those particles above solubility to grab on to and start to form
a solid and as you can see those particles on the graph are coming out of solution and
becoming a solid and the graph tells us how much is actually crystallized out of solution
the energy changes that take place here are very interesting when looked at from the perspective
of changing potential on kinetic energies in the cool down solution at room temperature the
solute above solubilities should solidify and get to a more favorable position the crystalline form
which is a lower potential energy which is the direction that nature is pushing it however it
needs a path to get to that lower potential energy which in this case is provided for by a small seed
crystal dropped into the stew saturated solution the path to crystallization lower potential energy
but where did that loss potential energy go law of conservation of energy it went to kinetic energy
the particles solidifying increased their kinetic energy which means an increase in temperature the
solidifying sodium acetate gets quite warm okay so we've been talking about sodium acetate here
but there's lots and lots of other compounds that will dissolve in water and they all have positive
slopes and this is what we would normally see and the graphs of solubilities of solids in water but
what about gases gases have negative slopes as you increase temperature gas has become less soluble
and in particular the fact that that happens with oxygen has great consequences for life in
water you can see here the different temperatures that occur at the ocean's surface what happens to
the availability of oxygen in the very cold water versus warmer water as the water gets
warmer the availability of oxygen decreases so where life thrives in the ocean is a compromise
between temperature and accident availability so the warmest water that the bright-red has less
diversity of life than if you go a bit further north or south or go to a greater depth of 100
to 200 meters where temperatures are cooler but there's more oxygen available I'm gonna go back
I want you to take a look at the carbon dioxide line at the bottom so carbon dioxide is not
very soluble and the solubility actually doesn't change much and this has a lot to do with ocean
acidification which we will get to a bit later and this has been a mad scientist production see