Solubility of Gases

Why is water such a great solvent? Water is a great solvent because it is made of very polar molecules that have a positive pole and a negative pole. δ- Which side of water is positive, and which side is negative? δ+

Dissolving is a physical change. When substances dissolve, they simply break apart into their smallest units. This is merely a change in size and shape. Cytoplasm is the aqueous solution found in living cells. It is full of the dissolved solids and gases necessary for life.

Solubility Unsaturated Solutions A solution is unsaturated when more solute can still be dissolved at a given temperature. At room temperature (20oC), 36 grams of NaCl will dissolve in 100 mL of water. Image courtesy of Sergei Smirnov, NMSU

Solubility Saturated Solutions A solution is saturated when a solvent has dissolved all the solute it can at a certain temperature. At room temperature (20oC), 36 grams of NaCl will dissolve in 100 mL of water. Image courtesy of Sergei Smirnov, NMSU

A solution is supersaturated when more solute has been dissolved than normally allowed at a given temperature and pressure. Supersaturated When a solution is placed under high pressure, more gaseous solute can be added. If it is placed under lower pressure, the gas will escape the solution.

How are temperature and the solubility of a gas related? As the temperature increases, the solubility of a gas decreases. As the temperature decreases, the solubility of a gas increases. This means that as the temperature goes up, LESS solute can be dissolved.

How are pressure and the solubility of a gas related? As the pressure increases, the solubility of a gas increases. As the pressure decreases, the solubility of a gas decreases. This means that as the pressure goes up, more gaseous solute can be dissolved.

Carbon dioxide gas is added to water under very high pressure to create carbonated water. Since the CO2 is added under such high pressure, the solution becomes supersaturated with CO2. This is why a soda bottles always fizzes and releases some gas when it is opened for the first time under normal atmospheric pressure.

As scuba divers travel deeper and deeper into the ocean, the pressure increases. This increases the amount of dissolved gases (particularly inert gases such as N2) in their blood stream. What will happen to the dissolved gases as the diver returns to the surface and the pressure decreases? The gas will come out of the blood to be breathed back out.

Your lungs are filled with tiny air sacs known as alveoli Your lungs are filled with tiny air sacs known as alveoli. This air sacs allow gases to be transferred between the lungs and the blood. When a scuba diver returns to the surface too quickly, the gases fill the alveoli rapidly and they are placed under too high of a pressure. Like tiny balloons overfilled with air, they begin to pop.

Hyperbaric means above the normal pressure. While decompression sickness, often called “The Bends”, can be fatal, it is treatable if caught early enough. Patients are often placed in a hyperbaric chamber. This increases the pressure of oxygen making it easier for the patient to breathe. Hyper means above Bar means pressure Hyperbaric means above the normal pressure.

Temperature and Gas Solubility Applications of Temperature and Gas Solubility Power plants and factories often use water as a coolant. This water absorbs heat and becomes very hot. Water is very good at this because it has such a high specific heat. Would gases be more or less soluble in this hot water? Gases are LESS soluble in hot water. The number of dissolved gases would decrease as the water became hotter and hotter.

Thermal Pollution When power plants and factories release the hot water back into rivers and lakes, it warms the water and decreases the amount of dissolved oxygen in the water. Without enough oxygen, plants and animals begin to die. This is known as thermal pollution. Is removing gases from the water a physical or a chemical change? Gases are just being separated from a mixture, so this is a physical change.

Which container would dissolve the most solid solute? Understanding the difference between the solubility of solids and gases. Which container would dissolve the most solid solute? Container T: It has the highest temperature. The pressure has no effect on the solubility of solids.

Understanding the difference between the solubility of solids and gases. Which container would dissolve the most gaseous solute? Container Q: It has the lowest temperature and the highest pressure.

Complete the following table showing by circling the effect of each change on each type of solute.

Why are solids and gases not considered complete opposites in terms of solubility? Solids and gases are complete opposites in terms of temperature; however, while pressure has a huge effect on gases, it has no effect on solids. They are not opposites in terms of pressure.