Nathan, a PhD chemist, has taught chemistry and physical science courses.
Acidic solutions are found everywhere in the natural world and are an important part of our everyday lives. This lesson defines acidic solutions and discusses their fundamental properties. Several examples of acidic solutions from the natural world and industry are also provided.
Acid Solution Basics
What do soft drinks, lemon juice, and your stomach have in common? Although these examples may seem unconnected, they all have a chemical link - they all contain acidic solutions.
All of these contain acidic solutions
In order to understand acidic solutions, we need to define acid. The most widely used definition of acids comes from the Bronsted-Lowry definition of acids and bases. According to Bronsted-Lowry, acids are compounds that donate a hydrogen ion (H^+). For example, hydrochloric acid (HCl) donates its hydrogen to sodium hydroxide (NaOH) to form water and sodium chloride (NaCl).The following is the reaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH).
Reaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH)
Acid solutions are commonly made through one of two ways. One way involves dissolving a compound in solid form, such as citric acid into water. The other way is to bubble gases, like carbon dioxide (or HCl) through water. In either case, the substance that dissolves in the water is known as the solute. The water that dissolves the solute is known as the solvent.
Acid Solution Properties
An important measurement that can be made to determine if a solution is acidic is the pH. The pH is a measure of the number of hydrogen ions that are present in the solution. Solutions that are neither acidic nor basic have a pH of 7. Basic solutions have pH values greater than 7, and acidic solutions have pH values below 7. The following table depicts the pH scale with the pH values of common acids.
The pH scale with the pH values of common acids
One way to determine the pH of an acidic solution is through the use of an indicator. An indicator is a compound or mixture of compounds that changes color under different pH conditions. For example, universal indicators turn red or yellow in acidic solutions and can be used to determine the pH of an acid with a fair degree of accuracy. This picture shows universal indicators added to different solutions.
Universal indicator added to different solutions
Since hydrogen ions are released by acids, acidic solutions can conduct electricity. The ability to cause electrical conductivity in solution classifies all acid solutions as electrolytes. The electrical conductivity of an acidic solution allows for pH measurements to be made digitally by a digital pH meter, like the one seen here.
A digital pH meter
While pH provides a quantitative measurement of acidity, acids can also be identified through qualitative properties. Acids generally taste sour. This property can be safely confirmed by tasting fruit juice like lemon or orange juice. The sour flavor of these juices comes from the dissolved citric acid.
Orange juice is acidic because it contains citric acid
Examples of Acid Solutions
There are many different acidic solutions that are found in the natural world, as well as in the realm of industry. These acid solutions range from hydrochloric acid to citric acid, and sulfuric acid to acetic acid. A brief list is given in the following table.
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Of all the acid solutions, one of the best-known examples is hydrochloric acid. Hydrochloric acid is produced naturally within our stomachs to aid digestion in addition to destroying harmful organisms that are unintentionally swallowed. Industrial uses for hydrochloric acid solutions include the refining of metals, metal plating, and the neutralization of excess bases used in chemical reactions.
Hydrochloric acid solution
Sulfuric acid is another example of an acidic solution that is crucial to our everyday lives. Solutions of sulfuric acid are used as the electrolyte solution in car batteries. This acidic solution is also used to make many other products, including fertilizers for agriculture.
Car battery containing sulfuric acid solution
Let's review. Acids are defined by the Bronsted -Lowry definition as compounds that donate a hydrogen ion in solution. Acidic solutions are made by dissolving the acidic compound (as the solute) in water (as the solvent). The pH of acidic solutions is less than 7. Acidic solutions are also characterized as being electrolytes that result in electrically conductive solutions. Another property of acidic solutions is a sour taste. Acidic solutions are found naturally in living organisms and are made synthetically for a wide array of industrial applications.
acids: compounds that donate a hydrogen ion (H^+) in solution
solute: a substance that dissolves in water
solvent: the substance that dissolves the solute
pH: a measure of the number of hydrogen ions that are present in the solution
indicator: a compound or mixture of compounds that changes color under different pH conditions
electrolytes: classification of acids based on the ability to cause electrical conductivity in a solution
Acidic solutions have pH values below 7 on the pH scale.
When you're done studying about acidic solutions, you should be able to accomplish these tasks:
Define acids and acidic solutions
Describe how to determine the pH of an acidic solution
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