Bases are the chemical opposite of acids. Acids are defined as compounds that donate a hydrogen ion (H+) to another compound (called a base). Traditionally, an acid (from the Latin acidus or acere meaning sour) was any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. Correspondingly, a base was any compound that, when dissolved in water, gives a solution with a hydrogen ion activity lower than that of pure water, i.e. a pH higher than 7.0 at standard conditions.

A soluble base is also called an alkali. A reaction between an acid and a base is called neutralization and this neutralization results in production of water and a salt. Volatile liquids (acids) when mixed with specific substances turn into salts. These substances form a concrete base and hence the name base was derived. Acids in general are H+ donors and Bases are H+ acceptors.

Comparison chart

Acid versus Base comparison chart
Definition Arrhenius Definition: An acid is any chemical compound which when dissolved in water gives a solution with a hydrogen ion activity greater than in pure water. Bronstead Lowry Definition: An acid is an substance which donates a proton. Arrhenius Definition: A base is an aqueous substance that can accept hydrogen ions. Bronstead Lowry Definition: A base is any substance which accepts a proton.
pH (measure of concentration of hydrogen ions in a solution) Less than 7.0. Greater than 7.0 and could go up to 14 in case of stronger bases.
Physical characteristics Depending on the temperature, acids can occur in solid, liquid or gaseous form. Taste sour. Bases feel slippery because of the reaction of the base with the oils of your hand. Frequently solids except ammonia which is a gas. Taste bitter.
Strength depends on concentration of the hydronium ions depends on concentration of the hydroxide ions
Phenolphthalein remains colorless Makes it pink
Other Properties Electrolytes, conduct electricity (because electrolytes), react with many metals. Electrolytes, conduct electricity, ranges from insoluble to so soluble that they can react with water vapor.
Dissociation Acids free hydrogen ions (H+) when mixed with water. Bases free hydroxide ions (OH-) when mixed with water.
Chemical Formula An acid has a chemical formula with H at the beginning of it. For example, HCl (Hydrochloric Acid). There is one exception to his rule, CH3COOH = Acetic Acid (vinegar) A base has a chemical formula with OH at the end of it. For example, NaOH (Sodium Hydroxide).
Examples Acetic acid i.e.CH3COOH and Sulfuric acid Sodium Hydroxide (NAOH) and Ammonia (NH3)
Litmus test Acids change litmus paper red. Bases change litmus paper blue.

Properties of acids vs bases

Bases have a slippery feel on fingers and taste bitter. They change litmus paper blue. Acids taste sour and create a stinging feeling on the mucous membranes. They change litmus paper red. They can react with bases to produce salts and water. They both conduct electricity depending on the dissociation of ions. Acids have a pH lesser than 7.0 and the lower it is, the stronger the acid becomes. Bases have a pH between 7 and 14. Higher the pH value, stronger will be the base. A pH level of 7 is a neutral substance which is water.

Litmus Test and Other Reactions

Litmus paper is made from dyes derived from lichens; it is water-soluble, meaning it can be fully dissolved in water. Acids turn blue litmus paper red, and bases turn red litmus paper blue. The following video shows how red and blue litmus paper reacts to ammonia, hydrochloric acid, water, and baking soda.

Strong acids have a corrosive effect on metals. They react with most of them to form hydrogen gas. Strong bases have a caustic effect on organic matter.

Differences in Applications for acids and bases

Acids are often used to remove rust from metals, as an electrolyte in batteries, for mineral processing, to produce fertilizers and gasoline and as additives in food and beverages. Bases are used primarily in cleaning as dishwashing and laundry detergents, oven cleaners and stain removers.

Types & Examples of Acids and Bases

Acids can be classified as Mineral acids, Sulfonic acids, Carboxylic acids, Vinylogous carboxylic acids and Nucleic acids. Some common acids include Hydrochloric acid (HCl), Sulfuric acid (H2SO4), Nitric Acid (HNO3), Acetic acid, Citric acid and Lactic acid amongst several others. Bases are of 2 types – a base and an alkali (a soluble base). Some common bases include Potassium Hydroxide (KOH), Sodium Hydroxide (NaOH) and Magnesium Hydroxide (Mg (OH)2).


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