Why Do Bubbles Form In A Glass Of Water That’s Left Out?

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Tap water contains atmospheric gases, such as nitrogen and oxygen, dissolved in it. As the glass filled with water sits out for a few hours, its temperature rises slightly (water gets warmer), which causes the dissolved gases in it to come out of the water and form bubbles along the inside of the glass.

Fill a glass with water (at or below room temperature) and leave it undisturbed for a few hours (you can do this using tap water). You will eventually notice that tiny bubbles appear along the side of the glass (on the inside).

Why does this happen?

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Solubility Of Gases In Water

The water we use daily comes from taps, passing through pipes before reaching large storage tanks. Due to the pressure in the pipes and the coolness of the water, certain gases like nitrogen and oxygen, which are abundant in our atmosphere, can be dissolved in the water.

Gases Are More Soluble In Water At Colder Temperatures

Gases are generally more soluble in water at a lower temperature. In other words, the solubility of gases in water decreases as the water temperature rises.

The graph below should help to visualize how the solubility of gases varies with changing temperature.

Solubility of Gases vs Temperature co2
The variation of solubility of carbon dioxide in water with increasing temperature

The downward trend of gases’ solubility with increasing temperature is quite similar to how vapor pressure increases with temperature. You see, more gas molecules are dissolved in water when it’s cold. However, when water starts getting warmer (i.e., the temperature rises), the kinetic energy of gas molecules also increases.

This allows those molecules to move more freely and break the intermolecular bonds that hold them together, thus escaping from the solution.

That’s why the solubility of gases decreases as temperature rises.

Danger To Aquatic Life Due To Changing Water Temperatures

The solubility of gases in water is influenced by temperature, which consequently has a direct impact on the lives of aquatic organisms. Fish and other aquatic life forms require oxygen for survival, which they obtain by absorbing the dissolved oxygen in the water through their gills. As the solubility of oxygen in water is higher in colder temperatures, it is crucial to maintain the water temperature below a certain limit.

Power plant near ocean lake
Waste products released by power plants increase the temperature of the water, thereby endangering marine life (Photo Credit: Flickr)

However, the current scenario is that water temperature is increasing beyond the limit, primarily due to human activities.

For instance, power plants discharge large amounts of hot water into water bodies, leading to a rise in water temperature and adversely affecting aquatic life. This is a highly undesirable outcome of the relationship between gas solubility and temperature.

Also Read: What Are The Bubbles Made Of When Water Boils?

The Solubility Of Gases In Water Increases With Increasing Pressure

Although liquids and solids exhibit practically no solubility change with changing water pressure, gases do. It has been observed that gases are more soluble in water at higher pressures. Carbonated drinks are excellent examples of this phenomenon.

Henry’s Law

The effects of changing water pressure on the solubility of gases can be explained by one of the gas laws known as Henry’s law. It states that “the amount of dissolved gas is proportional to its partial pressure in the gas phase.”

The simplest way to explain this dependence is that gas molecules are forced into the solution as pressure increases to relieve the applied pressure. The following image should help to visualize this better:

Pressure solubility gas effect oxygen atmosphere when pressure is increased more gas molecules are soluble at higher pressure

Also Read: What Is Henry’s Law?

Why Bubbles Form In A Glass Full Of Water Overnight

Due to the two physical phenomena described above, tap water becomes a good candidate for holding dissolved atmospheric gases, if not ideal. However, when this water is poured into a glass and left at room temperature for a few hours, the atmospheric pressure begins to drop as its temperature rises.

Tiny bubbles form in a glass of water overnight
Tiny bubbles form in a glass of water overnight (Photo Credit: Pixabay)

As a result, the dissolved gases in the water escape from the solution and form bubbles in the rough areas inside the glass. As the temperature does not change so quickly, it takes a few hours for the bubbles to appear on the glass.

Also Read: Science Behind The Shape Of Bubbles And Why They Pop

Last Updated By: Ashish Tiwari

References (click to expand)
  1. Battino, R., & Clever, H. L. (1966, August 1). The Solubility of Gases in Liquids. Chemical Reviews. American Chemical Society (ACS).
  2. https://antoine.frostburg.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml
  3. Laws of Gas Transport.
  4. Hildebrand, J. H. (1916, August). Solubility. Journal of the American Chemical Society. American Chemical Society (ACS).
About the Author

Ashish is a Science graduate (Bachelor of Science) from Punjabi University (India). He spearheads the content and editorial wing of ScienceABC and manages its official Youtube channel. He’s a Harry Potter fan and tries, in vain, to use spells and charms (Accio! [insert object name]) in real life to get things done. He totally gets why JRR Tolkien would create, from scratch, a language spoken by elves, and tries to bring the same passion in everything he does. A big admirer of Richard Feynman and Nikola Tesla, he obsesses over how thoroughly science dictates every aspect of life… in this universe, at least.

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