Hey it’s professor Dave, let’s discuss the solubility of gases.
Hey it’s professor Dave, let’s discuss the solubility of gases.

We know that solutions involve one or more solutes that have been dissolved in some solvent.
We know that solutions involve one or more solutes that have been dissolved in some solvent.

And typically, when we talk about solutions, we are looking at solids that have been dissolved
And typically, when we talk about solutions, we are looking at solids that have been dissolved

in a liquid to form a solution, such an aqueous solution of some ionic solid like sodium chloride.
in a liquid to form a solution, such an aqueous solution of some ionic solid like sodium chloride.

But in actuality, solutions can involve any combination of phases.
But in actuality, solutions can involve any combination of phases.

One possible type of solution involves gaseous solutes dissolved in liquid solvent.
One possible type of solution involves gaseous solutes dissolved in liquid solvent.

Different gases, like oxygen, hydrogen, methane, or carbon dioxide, will have greatly varying
Different gases, like oxygen, hydrogen, methane, or carbon dioxide, will have greatly varying

solubilities in water, and these solubilities depend on the ability of the different gas
solubilities in water, and these solubilities depend on the ability of the different gas

particles to make electrostatic interactions with water molecules in solution, just like
particles to make electrostatic interactions with water molecules in solution, just like

the way ionic solids dissociate in aqueous solution to make ion-dipole interactions.
the way ionic solids dissociate in aqueous solution to make ion-dipole interactions.

Take for example, oxygen and helium.
Take for example, oxygen and helium.

Oxygen is completely nonpolar, and helium is monoatomic, so there are no dipoles present
Oxygen is completely nonpolar, and helium is monoatomic, so there are no dipoles present

for interaction in either of these substances.
for interaction in either of these substances.

That means that oxygen and helium are only able to interact with water molecules in the
That means that oxygen and helium are only able to interact with water molecules in the

way of dipole-induced dipole interactions, which are rather weak.
way of dipole-induced dipole interactions, which are rather weak.

However, a molecule of oxygen is able to make much stronger interactions of these type than
However, a molecule of oxygen is able to make much stronger interactions of these type than

a helium atom can, as it is much larger than a helium atom, and can therefore can exhibit
a helium atom can, as it is much larger than a helium atom, and can therefore can exhibit

stronger momentary or induced dipoles.
stronger momentary or induced dipoles.

That’s why oxygen is three times more soluble in water than helium.
That’s why oxygen is three times more soluble in water than helium.

But oxygen is still one hundred times less water soluble than chloroform, because chloroform
But oxygen is still one hundred times less water soluble than chloroform, because chloroform

can participate in actual dipole-dipole interactions with water, which are possible because of
can participate in actual dipole-dipole interactions with water, which are possible because of

the formal dipole in the molecule.
the formal dipole in the molecule.

This is a much stronger interaction, which results in a much greater solubility.
This is a much stronger interaction, which results in a much greater solubility.

Remember the old saying, “like dissolves like”.
Remember the old saying, “like dissolves like”.

Since the dipole on every water molecule is interacting with the dipole on other water
Since the dipole on every water molecule is interacting with the dipole on other water

molecules, substances that can best approximate these types of interactions will be able to
molecules, substances that can best approximate these types of interactions will be able to

mix the most effectively amongst the water molecules, which means a greater solubility.
mix the most effectively amongst the water molecules, which means a greater solubility.

For this reason, we should also discuss the identity of the solvent, since that will make
For this reason, we should also discuss the identity of the solvent, since that will make

a big difference.
a big difference.

Something like oxygen will be 20 times more soluble in hexane than in water.
Something like oxygen will be 20 times more soluble in hexane than in water.

This is because hexane molecules are unable to make dipole-dipole interactions like polar
This is because hexane molecules are unable to make dipole-dipole interactions like polar

molecules do.
molecules do.

Instead, they make induced dipole interactions just like oxygen molecules, though of a much
Instead, they make induced dipole interactions just like oxygen molecules, though of a much

greater strength, since it is a larger molecule.
greater strength, since it is a larger molecule.

This means that when oxygen dissolves in hexane, it will simply replace some of these dispersion
This means that when oxygen dissolves in hexane, it will simply replace some of these dispersion

interactions with other dispersion interactions, which is a relatively small discrepancy in
interactions with other dispersion interactions, which is a relatively small discrepancy in

energy, rather if it is dissolved in water, where it has to disrupt the hydrogen bonds
energy, rather if it is dissolved in water, where it has to disrupt the hydrogen bonds

in pure water without being able to provide an equally strong interaction to replace them.
in pure water without being able to provide an equally strong interaction to replace them.

Solubilities of various substances are also affected by temperature.
Solubilities of various substances are also affected by temperature.

We know that increasing the temperature will typically increase the solubility of solids
We know that increasing the temperature will typically increase the solubility of solids

in aqueous solution.
in aqueous solution.

This is in part because the resulting additional kinetic energy can push the molecules in the
This is in part because the resulting additional kinetic energy can push the molecules in the

solid apart, but also higher temperatures increase the spontaneity of an entropically
solid apart, but also higher temperatures increase the spontaneity of an entropically

favorable of a process, and dissolution is entropically favorable, since matter is being
favorable of a process, and dissolution is entropically favorable, since matter is being

dispersed.
dispersed.

However, contrary to this trend, increasing the temperature of an aqueous solution will
However, contrary to this trend, increasing the temperature of an aqueous solution will

actually decrease the solubility of most gases in water.
actually decrease the solubility of most gases in water.

This is because the gas particles will have more kinetic energy, so they are moving more
This is because the gas particles will have more kinetic energy, so they are moving more

rapidly through the solution, and are therefore less capable of interacting with solvent particles.
rapidly through the solution, and are therefore less capable of interacting with solvent particles.

This also makes them less likely to be contained in solution, as they are more likely to have
This also makes them less likely to be contained in solution, as they are more likely to have

enough energy to escape the solution and move into the atmosphere.
enough energy to escape the solution and move into the atmosphere.

As we might imagine, this fact has serious ramifications for our ecosystem, since in
As we might imagine, this fact has serious ramifications for our ecosystem, since in

addition to the slow and steady progress of climate change, some industrial processes
addition to the slow and steady progress of climate change, some industrial processes

increase the temperature of nearby rivers and lakes, which reduces the solubility of
increase the temperature of nearby rivers and lakes, which reduces the solubility of

oxygen and thus reduces the concentration of oxygen in these bodies of water.
oxygen and thus reduces the concentration of oxygen in these bodies of water.

Aquatic life like fish need oxygen to breathe, so if enough oxygen escapes the water, many
Aquatic life like fish need oxygen to breathe, so if enough oxygen escapes the water, many

fish can die, which can be catastrophic for that biosystem, since other organisms eat
fish can die, which can be catastrophic for that biosystem, since other organisms eat

those fish.
those fish.

Beyond this, there can be great impact on the economy of the area, if those fish are
Beyond this, there can be great impact on the economy of the area, if those fish are

depended upon for food or profit.
depended upon for food or profit.

As we have just discussed the dependence of gas solubility on temperature, let’s also
As we have just discussed the dependence of gas solubility on temperature, let’s also

discuss the solubility of a gas as it relates to the partial pressure of that gas.
discuss the solubility of a gas as it relates to the partial pressure of that gas.

Specifically, the greater the partial pressure of a specific gas directly above a liquid
Specifically, the greater the partial pressure of a specific gas directly above a liquid

solution, the higher the solubility of that gas will be.
solution, the higher the solubility of that gas will be.

For example, carbonated beverages are prepared by exposing a liquid to a high pressured sample
For example, carbonated beverages are prepared by exposing a liquid to a high pressured sample

of carbon dioxide gas.
of carbon dioxide gas.

Because there are so many carbon dioxide molecules that are colliding with the gas-liquid interface,
Because there are so many carbon dioxide molecules that are colliding with the gas-liquid interface,

many more of these molecules will enter the solution, which results in a saturation of
many more of these molecules will enter the solution, which results in a saturation of

the beverage with carbon dioxide.
the beverage with carbon dioxide.

This happens during the packaging of any can or bottle of soda.
This happens during the packaging of any can or bottle of soda.

Then, once the container is opened at home, much of that carbon dioxide will quickly escape,
Then, once the container is opened at home, much of that carbon dioxide will quickly escape,

which results in the familiar hiss we hear upon breaking the vacuum seal.
which results in the familiar hiss we hear upon breaking the vacuum seal.

And now we know a bit about the solubility of gases.
And now we know a bit about the solubility of gases.