Acid, Base and Neutralisation
Acid:
Definition - An acid is a substance that increases the concentration of hydrogen ions (H⁺) in a solution.
When an acid dissolves in water, it releases hydrogen ions:
Hydrochloric acid → hydrogen ion + chloride ion
That release of H⁺ ions is what gives acids their characteristic behavior.
Main properties of acids:
• They release hydrogen ions (H⁺) in water, this is the defining chemical property of acids.
• They have a pH less than 7, the lower the pH, the more acidic the substance is.
• They turn blue litmus paper red, this is a common test for acids.
• They taste sour, Example citric acid in lemons.
• They react with metals, many acids react with metals like zinc or magnesium to produce hydrogen gas.
• They conduct electricity in water, because acids form ions in solution.
• They react with bases to form salt and water, this is called a neutralization reaction.
Types of acids and their uses:
• Hydrochloric acid — used for cleaning metals, making chemicals, and helping digestion in the stomach.
• Nitric acid — used to make fertilizers, dyes, and explosives.
• Citric acid — found in citrus fruits; used in drinks, candies, and cleaning products.
• Carbonic acid — present in soft drinks and carbonated beverages.
Base:
Definition-A base is a substance that reduces the amount of free hydrogen ions (H+) in a solution, and neutralises it.
Main properties bases: • They release hydroxide ions (OH-) in water or accept hydrogen ions (H+), this is the defining chemical property of bases.
• They have a pH greater than 7, the higher the pH, the stronger the base.
• They turn red litmus paper blue, this is a common test for bases.
• They taste bitter, though chemicals should never be tasted directly in a lab.
• They feel slippery or soapy, examples include soap solutions.
• They conduct electricity in water, because bases form ions in solution.
• They react with acids to form salt and water, this is called a neutralization reaction.
• Strong bases can be corrosive, meaning they can damage skin and materials.
Types of bases and their uses:
Zinc hydroxide — used in chemical manufacturing and laboratory work.
Copper hydroxide — used as a fungicide and pigment.
Lithium hydroxide — used in batteries and air purification systems.
Barium hydroxide — used in chemical testing and lubricant production.
Neutralisation:
Acids release H+ ions.
Bases remove or balance those H+ ions.
That is why acids and bases neutralize each other.
Some bases release hydroxide ions (OH-) in water.
Those hydroxide ions combine with hydrogen ions:
• H+ + OH- = H20
This forms water.
Examples:
Soap
Toothpaste
Baking soda
Sodium hydroxide
A common mistake is thinking “base” only means “contains OH-. ” That is not always true. Some bases, like ammonia (NH3), do not contain hydroxide directly but still behave as bases because they accept H+ ions.