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Factors Affecting the Solubility of Gases

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Lesson Focus

Factors Affecting the Solubility of Gases


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You will explore the change in solubility of a gas in a liquid while the pressure and temperature of the solution are changed.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Explain that the solubility of a gas in a liquid is directly proportional to pressure.
  • Explain that the solubility of a gas in a liquid is directly proportional to temperature.
  • Identify bromothymol blue and phenolphthalein as pH indicators.
  • Explain why bubbles rise faster out of a warm soda than a cold soda.

Everything You'll Have Covered

A solution is a homogeneous mixture of two or more substances. The amount of a substance that can dissolve into another substance determines the solution's solubility. Solutions can be made of any combination of solids, liquids, and gases.

Gases are commonly found dissolved in liquids. The air we breathe dissolves into our blood for our bodies to use. Soft drinks have dissolved carbon dioxide in them, which makes the bubbles. The amount of a gas that can be dissolved into a liquid can change depending on what type of environment the solute and solvent are in. To increase the amount of gas dissolved in a liquid, two variables can be changed - temperature and pressure.

As temperature increases in a solution, the kinetic energy of the gas molecules increases, resulting in a decrease in solubility. The gas will rise to the top of the solution, and bubble out of the solution, displaying a direct relationship between temperature and solubility. Pressure and solubility also have a direct relationship, but unlike temperature, as pressure increases, solubility also increases. As pressure is exerted on top of the liquid, the gas inside the solution has to overcome the pressure to escape from the liquid. As pressure increases, it becomes more difficult for the gas to escape, thus remaining dissolved in the liquid.

Since solutions are homogeneous mixtures, identifying individual components is difficult. One method to determine the solubility of a gas is by measuring the pH of the solution. Carbon dioxide will become carbonic acid in a solution. Since an acid has a pH level below seven, a chemical indicator can be used to determine the amount of gas dissolved in the solution. As more gas dissolves, the pH will decrease causing the solution to become more acidic. Bromothymol blue is an indicator that is green when in a slightly acidic solution and turns yellow as the acidity increases.

Ammonia, when in a solution, turns into ammonium, which is basic. To determine the degree of alkalinity of a solution, phenolphthalein is used as the chemical indicator. Phenolpthalein makes a basic solution pink. The more basic the solution is, the darker the pink color is, indicating an increase in pH and an increase in the amount of ammonia dissolved in the solution.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Learners should be familiar with these terms: acid, base, indicator, pH, solubility, solute, solution, solvent, and states of matter.
Course Chemistry
Type of Tutorial Experiment
Key Vocabulary 3D, acid, ammonia