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Base (chemistry)

physical science Maturity 9-11 Next article →

In chemistry, a base is a substance that reacts with an acid. This relationship makes bases the chemical opposites of acids. When they meet, they undergo a process called neutralization. This reaction produces water and a salt.

Handmade soap cropped and simplified
Handmade soap cropped and simplified

Bases are essential to many processes in our world. They are found in everything from household cleaning products to the medicines we take for stomach aches. Understanding bases requires looking at how they behave at a molecular level.

Scientists use three main definitions to describe how a base works. The first is the Arrhenius definition, proposed by Svante Arrhenius in 1884. An Arrhenius base is a substance that dissociates in water to form hydroxide ions (OH−). These ions can react with hydrogen ions (H+) from an acid to form water. The second is the Brønsted–Lowry theory from 1923. This theory defines a base as a substance that can accept hydrogen cations, which are also called protons. This definition is broader because it includes substances like ammonia (NH3) that do not contain hydroxide ions.

Hydrochloric acid ammonia
Hydrochloric acid ammonia

The third is the Lewis theory. G. N. Lewis realized that bases can form bonds by donating an electron pair. A Lewis base is an electron pair donor. It shares these electrons with a Lewis acid, which is an electron acceptor. This theory is the most general of all three.

Bases can be categorized by their strength. A strong base is one that is completely protonated when it touches water. This happens because of a process called the leveling effect. Common strong bases include hydroxides of alkali metals and alkaline earth metals. Examples include sodium hydroxide (NaOH) and calcium hydroxide (Ca(OH)2).

Sodium hydroxide image
Sodium hydroxide image

Some bases are even more powerful and are called superbases. These are so strong they cannot exist in water. If you put a superbase like butyl lithium into water, it would react immediately. Other bases are considered weak. A weak base, such as ammonia or baking soda, does not fully ionize in a water solution. The extent of this reaction is measured by an equilibrium constant called Kb.

History shows how our understanding of these substances has grown. In the mid-18th century, G.-F. Rouelle first proposed that bases react with acids. This moved chemistry away from the older ideas of alchemy. Later, the work of Arrhenius, Brønsted, Lowry, and Lewis provided the mathematical and structural rules we use today. These discoveries allowed chemists to predict how different molecules will interact. We can now calculate the exact strength of a solution using the pH scale. A basic solution at standard conditions always has a pH greater than 7.0.

Bases have many physical properties you can observe. Many aqueous solutions of bases are slippery to the touch. They can also have a bitter taste. Bases change the color of chemical indicators. For example, they turn red litmus paper blue and turn phenolphthalein pink.

BARIUM HYDROXIDE IMAGE
BARIUM HYDROXIDE IMAGE

Concentrated or strong bases are often caustic, meaning they can damage organic matter. They can also react violently when mixed with acidic substances. In a laboratory, bases can also conduct electricity when they are dissolved in water or in a molten state.

We see the practical use of bases in everyday life. Many antacids used to treat stomach acid are suspensions of metal hydroxides. These include aluminum hydroxide and magnesium hydroxide. These specific bases are useful because they have low solubility. This prevents them from causing harm to the tissues in your mouth or esophagus.

BARIUM HYDROXIDE IMAGE
BARIUM HYDROXIDE IMAGE

Another common use is in the production of soap. Soap is a weak base created by reacting fatty acids with sodium hydroxide or potassium hydroxide.

Handmade soap cropped and simplified
Handmade soap cropped and simplified

This shows how a strong base can be transformed into a gentle cleaning agent.

Bases are also connected to the study of complex molecular structures. Some bases, like those containing carbon, nitrogen, or oxygen, can be very strong if they lack resonance stabilization. When they do have resonance stabilization, they become weaker, such as sodium acetate. The study of bases also connects to the study of metals. Many Lewis acids are high oxidation state metal ions like iron (Fe3+) or manganese (Mn7+). When a base bonds with these ions, it forms what is called a coordination complex. This deepens our understanding of how atoms build the world around us.

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🖼️ Images & Media (4)
File:Handmade soap cropped and simplified.jpg
Handmade soap cropped and simplified.jpg
File:Hydrochloric acid ammonia.jpg
Hydrochloric acid ammonia.jpg
File:Sodium hydroxide image .jpg
Sodium hydroxide image .jpg
File:BARIUM HYDROXIDE IMAGE.jpg
BARIUM HYDROXIDE IMAGE.jpg
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