Acids

Navigate the knowledge tree: 🌿 Skills ➡ Life Processes

Types of Acids

In everyday life, when we say a substance is acidic, we usually mean that it has a sour or sharp taste. Lemon juice and vinegar are acidic. When we use the word 'acid', we usually refer to a chemical which will attack metals or other substances. Sulfuric acid in a car battery is a powerful acid which will strip paint if splashed.

In Science, acids belong to a family of chemicals which all display acidic properties. These properties relate to the nature of acids and the way they react with other chemicals. Acids can be solid (e.g. tartaric acid powder) or liquid (e.g. sulfuric acid), or gaseous (e.g. hydrogen chloride). Acids can also dissolve in water to give acidic solutions (e.g. citric acid in lemon juice).

There are two types of acids: mineral acids and organic acids.

Mineral acids

Mineral acids are manufactured from minerals. The acids you use in the laboratory are mostly mineral acids. Some examples are:

Hydrochloric acid (HCl) is a mineral acid commonly found in the laboratory and in the stomach.

Sulfuric acid (H₂SO₄) is a mineral acid commonly found in the laboratory and in car batteries.

Nitric acid (HNO₃) is a mineral acid commonly found in the laboratory and in producing nitrogen-based fertilisers.

Phosphoric acid (H₃PO₄) is a mineral acid commonly found in the laboratory and in producing fertilisers.

Organic acids

Organic acids are often found in nature and all contain the element carbon. Some examples are:

Acetic acid (CH₃COOH) is an organic acid found in vinegar. Link to molecular structure.

Citric acid (C₆H₈O₇) is an organic acid found in citrus fruits like oranges and lemons.

Tartaric acid (C₄H₆O₆) is an orgaic acid commonly found in baking ingredients.

Lactic acid (C₃H₆O₃) is an organic acid commonly found in milk products (e.g. yogurt) and fermented food (e.g. kimchi, sauerkraut).

Acids can be classified as strong or weak Mineral acids are usually strong, while organic acids, like citric acid are mostly weak.

Properties of Acids

An acid can be defined as a substance which displays acidic properties.

Acids taste sour
Acids turn blue litmus paper red
Acids attack some metals to give hydrogen gas
Acids attack marble chips to give carbon dioxide gas

But this definition is circular - an acid displays acidic properties, but acidic properties are just the properties of acids. An acid could be better defined as any substance which releases 'acid particles' which dissolved in water. But what are these 'acid particles'?

If you look at the chemical formulas of the acids in the "Types of Acids" section above, you will notice that the only type of atom they have in common is H, hydrogen. Acids are all compound sbecause they contain atoms of different elements bonded together. Acids are all hydrogen compounds. Hydrogen atoms in a compound exist as a nucleus of a single proton with shared eletrons whizzing around it. If hydrogen atoms become separated from the acid, they lose all electrons to become charged particles called ions. Each ion is just a lone proton with a positive charge. The formula for a hydrogen ion is H⁺.

An acid is any substance which releases hydrogen ions when it dissolves in water. Hydrogen ions are the 'acid particles'. An acid only displays its properties when it dissolves in water. When an acid releases hydrogen ions in water, the solution is said to be an acidic solution.

A strong acid like hydrochloric acid (HCl) fully dissociates (breaks up) and releases many hydrogen ions. A weak acid like acetic acid (CH₃COOH) only partially dissociates and releases few hydrogen ions.

Bases and Alkalis

Bases are another family of chemicals which have the opposite property to acids. Bases remove acid particles from a solution. Sodium hydroxide (Mr Muscle), ammonium hydroxide (Janola) and magnesium hydroxide (Mylanta) are bases.

An alkali is a base which will dissolve in water. A soluble base forms an alkaline solution with a pH above 7. All alkalis are bases.

Sodium hydroxide (NaOH) is an alkali base commonly found in oven cleaners.

Ammonium hydroxide (NH₄OH) is an alkali base commonly found in household cleaners.

Magnesium hydroxide (Mg(OH)₂) is an alkali base that is commonly found in indigestion tablets.

Calcium hydroxide (Ca(OH)₂) is commonly found in white wash. It is NOT an alkali and is not soluble in water.

More on Acids & Bases

📕 article 📸 image 🎮 interactive 🎦 video

Glossary

Key terms and definitions.

Page updated

Google Sites

Report abuse