(POS) Factors Affecting Solubility Lesson

Factors Affecting Solubility

There are two direct factors that affect solubility: temperature and pressure. Temperature affects the solubility of both solids and gases, but pressure only affects the solubility of gases.

Temperature has a direct effect on solubility. For the majority of ionic solids, increasing the temperature increases how quickly the solution can be made. As the temperature increases, the particles of the solid move faster, which increases the chances that they will interact with more of the solvent particles. This results in increasing the rate at which a solution occurs.

Temperature can also increase the amount of solute that can be dissolved in a solvent. Generally speaking, as the temperature is increased, more solute particles will be dissolved. For instance, when you add table sugar to water, a solution is quite easily made. When you heat that solution and keep adding sugar, you find that large amounts of sugar can be added as the temperature keeps rising. The reason this occurs is that as the temperature increases, the intermolecular forces can be more easily broken, allowing more of the solute particles to be attracted to the solvent particles. There are other examples, though, where increasing the temperature has very little effect on how much solute can be dissolved. Table salt is a good example: you can dissolve just about the same amount of table salt in ice water as you can in boiling water.

For all gases, as the temperature increases, the solubility decreases. The kinetic molecular theory can be used to explain this phenomenon. As the temperature increases, the gas molecules move faster and are then able to escape from the liquid. The solubility of the gas, then, decreases. For an explanation about the solubility of gases, please watch the video clip below.  

Look at the graph below. We can summarize how temperature affects solubility by looking at this graph:

The second factor, pressure, affects the solubility of a gas in a liquid but never of a solid dissolving in a liquid. Pressure is the force pushing against a given area. When pressure is applied to a gas that is above the surface of a solvent, the gas will move into the solvent and occupy some of the spaces between the particles of the solvent. As you heard in the video above a good example is carbonated soda. Pressure is applied to force the CO₂ molecules into the soda. The opposite is also true.

When the gas pressure is decreased, the solubility of that gas is also decreased. When you open a can of carbonated beverage, the pressure in the soda is lowered, so the gas immediately starts leaving the solution. The carbon dioxide stored in the soda is released, and you can see the fizzing on the surface of the liquid. If you leave an open can of soda out for a period of time, you may notice the beverage becoming flat because of the loss of carbon dioxide.

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