ACID, BASE, SALT Subtitle What is the taste of these lemons? ACID • Acids taste sour, the word ‘acid’ derived from from a Latin word which means “sour” • An acid is a substance that gives hydrogen ions (H+) when dissolved in water • Acids are found in many substances including food items but their presence in fruit is very prominent, e.g. Citric acid is present in sitrus fruit such as lemon and orange • Some acids are widely used in laboratory, like hydrochloric acid and nitric acid • Our body contains some very common acids like dilute hydrochloric acid in the stomach • Bee stings are acidic in nature • All acids generate hydrogen gas on reaction with metals • In fact, all acids contain hydrogen ions (H+) • The acids we use in the laboratory are very strong, they are corrosive and can burn your skin BASE • Bases taste bitter • The solution of a base in water is called alkali • Bases are found in household cleaners to clean grease from windows and floors. They also present in soaps, toothpaste, egg whites, sea water • A base is a substance that gives hyroxyl ions (OH-) when dissolved in water • Bases are chemical opposite of acids • Strong bases can also burn our skin • Wasp sting are basic in nature SALT • A salt results when an acid reacts with a base, both are neutralised • The H+ and OH- ions combine to form water • The non metalic ions of the acid and the metal ions of the base form the salt • Acid + Base Salt + Water • HCl + NaOH NaCl + H2O • NaCl is sodium chloride ( table salt) • The salt ions normally stay in solution. The salt crystalizes out when the water is removed How do we know that the solution is acid or base? • Acidity is measured on a scale called pH • The value of pH determines how acidic or basic a solution is • A pH of 1 is very acidic, a pH of 14 is a strong alkali • A neutral solution (pure water) has a pH of 7 • There are chemicals that change colour at different pH value. These are called indicators • One of the famous indicator is Litmus • Litmus is a purple dye extracted from the lichen plant • Litmus turns red when the pH is less than 7 (acidic) and turns blue when the pH is greater than 7 (basic) Litmus Paper Litmus test Natural Indicators • Natural Indicator is a type of indicator that can be found naturally and can determine whether the substance is an acidic substance or a basic substance. Some examples of natural indicators are red cabbage, turmeric, grape juice, turnip skin, curry powder, cherries, beetroots, onion, tomato, etc. • Some flowers like hydrangeas can determine the acidity or basicity of the soil. These flowers become blue if the soil is acidic, purple if the soil is neutral and pink if the soil is basic. The intensity of the color depends on the amount of acid or base present in the soil. Soil which is highly acidic bears deep blue flowers, whereas soil which is highly basic yields deep pink flowers.
