Acids and bases: differences, characteristics, examples

The most important definitions, such as Brönsted-Lowry, or Arrhenius, focus more on the release of H 3 O + (hydronium) or OH  (hydroxyl) ions by these substances. Either in its pure forms or dissolved in water.

A definition that arises as a consequence of the above is the following: acids dissolved in water generate solutions with pH values ​​lower than 7, while dissolved bases produce solutions with pH values ​​higher than 7. The pH is precisely a form of express how acidic or basic a liquid is taking into account the concentration of H 3 O + .

Therefore, acidic substances, such as orange juice, have a pH less than 7 and many H 3 O + ions . While the bases, like the legía, have a pH greater than 7 and many OH  ions .



Substance type

Sour substances.

Soapy substances.


pH less than 7.

pH greater than 7.





They stain litmus paper red.

They stain litmus paper blue.


They contain and release hydrogens.

Some have OH groups.


They are corrosive.

They are not corrosive.


Hydrochloric acid, sulfuric acid, chloric acid.

Lithium hydroxide, ammonia, sodium hydroxide.


Orange juice is one of the best known acid representatives of our daily life

Characteristics of acids

Acidic substances have certain characteristics:

Sour taste

Acids taste sour. Routinely, a type of flavor is designated by the term ‘sour’. Thus, it is said that the lemon juice and the liquid of some chewing gums are acidic, since their flavors are sour and strong on the palate.

They stain litmus paper red

Acids are substances capable of turning the color of litmus paper from blue to red. Litmus is part of a group of substances that can change color depending on the degree of acidity or basicity of the environment in which they are found. These substances are called pH indicators.

Contain and release hydrogens

Acids are chemical compounds that have the chemical element hydrogen (H) in their structure, which gives them their characteristic of acidity.

Many other substances also contain hydrogen, but cannot release it as with acids. When released, hydrogen is in the form of an ion or cation H + . These H + , when meeting the water molecules, add to them to form the H 3 O + ions .

They carry electrical current

Due to the H + atoms that are released when acids dissolve in water, they are capable of transporting electricity through the use of cells or batteries.

They are corrosive

There are strong acids that are very corrosive. Therefore, contact with them should be avoided as they can cause severe physical damage. Even weak acids, at very high concentrations, such as acetic (vinegar) can burn the skin and pharynx if you breathe its vapors.

Strong and weak

Strong acids produce a high concentration of H 3 O + ions when they dissolve in water. Hydrogen atoms in strong acids are said to be easily dissociable. Meanwhile, weak acids release few hydrogen atoms and, therefore, produce a lower concentration of H 3 O + ions .

Strong acids have a very low pH, which depending on the concentration and strength of the acid, can be 1 or less. On the other hand, weak acids have a higher acidic pH, which can be for example 4 or 5.

Strong acids have an odor that produces a burning sensation. While, weak acids do not present this type of odor, even in some cases they present pleasant odors. However, there are many exceptions, so it is not recommended to go around smelling even weak acids.

Strong acids are good carriers of electricity. In contrast, weak acids are poor conductors of electricity by releasing few H + atoms .

Strong acids are capable of attacking metals, such as zinc, forming large amounts of hydrogen gas bubbles. This reaction is not produced by weak acids.

Examples of acids

Strong acids

-HCl: hydrochloric acid

-H 2 SO 4 : sulfuric acid

-HBr: hydrobromic acid

-HI: hydroiodic acid

-HNO 3 : nitric acid

-HClO 4 : perchloric acid

-HClO 3 : chloric acid

Weak acids

-CH 3 COOH: acetic acid

-HNO 2 : nitrous acid

-H 2 CO 3 : carbonic acid

-H 3 PO 4 : phosphoric acid

-C 3 H 5 O (COOH): citric acid

-HF: hydrofluoric acid

-H 2 SO 3 : sulfurous acid


Characteristics of the bases

The bases have the following characteristics:

 They produce a slimy or soapy sensation on the fingers, making objects held by the hands become slippery.

 They have a bitter taste.

 They can react with acids, producing the formation of compounds called salts. In some cases, these can precipitate or sink in the water. Likewise, in the reaction of a base with an acid, water is formed.

– They turn the color of litmus paper in blue, indicating that the solution has a pH greater than 7 or alkaline.

 Some bases have OH groups in their chemical formula, called hydroxyl, which are made up of a hydrogen atom and an oxygen atom.

Strong and weak

Strong bases are chemical compounds that have one or more OH groups in their chemical structure, which when they come into contact with water acquire a negative charge, OH  .

Meanwhile, weak bases do not have hydroxyl groups in their chemical formula. However, weak bases when reacting with water also produce OH  ions or anions .

Strong bases, such as sodium hydroxide, have very high pH values, close to 14. While, weak bases have lower pH, such as ammonia, which has a pH of 11.

Strong bases are used in homes to unclog drains. Such is the case of potassium hydroxide. Meanwhile, weak bases are used in cleaning tasks, like the ammonia present in many cleaners.

Examples of bases

Strong bases

-LiOH: lithium hydroxide

-NaOH: sodium hydroxide

-KOH: potassium hydroxide

-RbOH: rubidium hydroxide

-CsOH: cesium hydroxide

-Sr (OH) 2 : strontium hydroxide

-Ba (OH) 2 : barium hydroxide

Weak bases

-NH 3 : ammonia

-NHEt 2 : diethylamine

-NH 2 CH 3 : methylamine

-C 5 H 5 N: pyridine

Differences between acids and bases

Ions that release

Acids release H + or H 3 O + atoms when they dissolve in water. Meanwhile, bases release or produce OH  ions in contact with water .

PH values

Acids have a pH value between 0 and 7. While bases have a pH value between 7 and 14. Therefore, acids turn litmus paper red and bases turn it blue.

Formation reactions

Acids originate from the reaction of oxides of non-metallic elements, for example chlorine, sulfur, etc., with water, or they are also formed when hydrogen combines with a non-metallic element and then the compound formed dissolves in water (HF, HCl, HBr, etc.).

Bases are produced by the reaction of the oxide of a metal, for example iron, copper, magnesium, etc., with water. It must be remembered that an oxide is the combination of oxygen atoms with any other chemical element.

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