Let’s look at how temperature can affect solubility.
Solubility tells us the maximum amount of solute that can dissolve in a certain amount
of solvent.
In this video, we’ll look at how temperature affects the solubility of solids dissolving
in water, and how it affects the solubility of gases dissolving in water.
We’ll look at some patterns for temperature and solubility,
And we’ll see some real-life examples.
First off, let’s look at the solubility of solids dissolving in water.
How does temperature affect this?
You’ve probably seen this for yourself.
Say you have hot coffee and iced coffee.
You can dissolve lots of sugar into hot coffee. Many many many spoons of sugar can dissolve
in hot coffee: just a ton.
But for cold iced coffee, a lot less sugar dissolves.
After a certain point, you can stir as much as you want, but you just can’t get any
more to dissolve.
The sugar is just going to end up on the bottom of the glass, not dissolved.
So more sugar dissolves in the hot coffee, and less dissolves in the cold iced coffee.
What’s true for sugar is true for most other solids as well.
Let’s describe this trend.
At higher temperatures, more solute (more sugar) can dissolve.
This means that as temperature goes up, solubility goes up as well.
Now, what about the other direction?
When we look at the cold iced coffee, we see that at lower temperature, less solute
can dissolve.
So speaking in terms of solubility, as temperature goes down, solubility does
as well.
Here, solubility and temperature have a direct relationship: they move in the same direction:
they both go up, or they both go down.
Now what we see here is typically true, but the full story is a little more complicated.
To get that full story, let’s take a look at a graph.
Check it out.
This shows the solubility of various solids in water, at different temperatures.
This axis is temperature.
And this axis is solubility: how much solute can dissolve in a certain amount of water.
The different lines are different chemicals: this is potassium nitrate, and we have
sugar, and a bunch of others.
And just looking at this, you can see that most of these lines really go up.
So yeah, the solubility of most solids in water increases as the temperature of the
solution increases.
But this isn't always true, there are some things
to note.
Look at sodium chloride here, it's this green line.
Its solubility doesn’t change much as temperature increases.
It just goes up a tiny tiny bit.
And a few compounds are real exceptions: they actually get less soluble with temperature.
For example, cerium sulfate is a compound that becomes less soluble as temperature rises.
You can see it right here.
Temperature goes up, solubility goes down.
So there are some exceptions.
And to account for such exceptions, we’ll say that “generally” or “usually,”
the solubility of solids in water increases as the temperature of the solution increases.
That’s the main point here.
Next, let’s see how temperature affects the solubility of gases.
For gases, we see pretty much the opposite trend that we see for solids.
Here's the solubility graph for gases.
These lines are some different gases.
And check it out: the pattern is different here.
In this case, the gas solubility goes down as temperature increases.
For gases, when you increase the temperature of the solution, the solubility decreases.
It’s the reverse of what we see with solids.
Let’s use this graph to look at the trend a little deeper.
As we increase the temperature, we decrease the gas solubility.
And that also means that as we decrease the temperature, we increase the solubility.
Here, solubility and temperature move in opposite directions.
It can also be helpful to think about these trends in terms of the amount of gas that
can dissolve.
This means that at higher temperatures, less gas can dissolve.
And at lower temperatures, more gas can dissolve.
Also, it’s worth mentioning that this is pretty much always true.
We don’t really have the exceptions that we saw for solids.
So this is the trend for gases.
And we call this an inverse relationship: as one goes
up, the other goes down, and vice versa.
. . Now, let’s take a look at two examples of temperature and gas solubility.
Here’s something that you’ve probably experienced yourself.
As soda gets hotter, it becomes more bubbly.
There are lots of big bubbles in warm soda, but there are fewer, smaller bubbles in colder
soda.
The reason for that is because of these gas solubility trends.
Soda is a solution where carbon dioxide gas is dissolved in water.
So let’s see how much gas can dissolve at the different temperatures.
For the colder soda.
At low temperature, solubility is higher, so the gas is more soluble, and more of it
stays dissolved in the soda.
Then, as the temperature increases…
The solubility goes down, the gas is less soluble so less of it dissolves.
More gas dissolves at the lower temperature, less gas at the higher temperature.
Now what about the bubbles here?
When gas can’t dissolve any more, it bubbles out.
At high temperature, less gas can dissolve, so more of it is going to bubble out.
And at low temperature, more gas dissolves, so less of it is going to bubble out: it’s
going to stay dissolved in the liquid.
So, as temperature increases, less gas dissolves.
The gas that can’t dissolve anymore is gonna bubble out, and that’s why soda is more
bubbly at higher temperature.
. . OK, let’s see the last example.
The way gases dissolve in water is very important for the environment, and temperature can affect
this.
Let’s take a look at a lake.
The water in that lake has oxygen gas dissolved in it.
Here it is: a bunch of O2’s: molecules of oxygen gas
Fish (and other living things) are able to pull that dissolved oxygen out of the water.
That’s how fish breathe: using their gills, they pull in oxygen gas that was dissolved
in the water.
But the amount of oxygen gas that's dissolved depends on the temperature of the
water.
And that can change.
Sometimes, power plants or factories dump hot water into lakes.
This may not seem like a big deal,
but that hot water raises the temperature of the lake.
As the lake gets hotter, what’s going to happen to the solubility of this dissolved
oxygen?
As the temperature rises, gas solubility goes down.
Less and less oxygen will be able to dissolve in the water.
It might bubble right out.
So oh, we lose that one, oh, we lose another one.
And eventually, it could get to a point where there’s not enough dissolved oxygen for
the fish, and they die, along with other living things.
This is an example of what we call “thermal pollution.”
If you change the temperature of something in the environment, it can be a really big
problem, particularly for water ecosystems.
So, as we’ve seen with this example and others:
as temperature rises, less gas can dissolve.
So let’s review everything that we've talked about.
For solids dissolved in water, there is a direct relationship between temperature
and solubility.
If the temperature increases, the solubility generally increases as well.
There may be rare exceptions, but it’s a pretty reliable relationship.
And this is why more sugar dissolves in hot coffee, and less dissolves in iced coffee.
For gases dissolved in a liquid, there is an inverse relationship between temperature
and solubility.
If the temperature increases, the solubility decreases.
That's why soda gets more bubbly at higher temperatures.
Less gas dissolves when it's hotter, so the extra gas bubbles out.
And if a lake temperature rises less oxygen will dissolve, which can have a very negative
impact on the living things in that lake.