Acids, Bases and Salts PDF - 2024-25

Paris, the substance which doctors use as plaster for supporting fractured bones in the right position. Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass. 1 1 CaSO 4. H2 O + 1 H2O → CaSO4.2H2 O...

Paris, the substance which doctors use as plaster for supporting fractured bones in the right position. Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass. 1 1 CaSO 4. H2 O + 1 H2O → CaSO4.2H2 O 2 2 (Plaster of Paris) (Gypsum) Note that only half a water molecule is shown to be attached as water of crystallisation. How can you get half a water molecule? It is written in this form because two formula units of CaSO4 share one molecule of water. Plaster of Paris is used for making toys, materials for decoration and for making surfaces smooth. Try to find out why is calcium sulphate hemihydrate called ‘Plaster of Paris’ ? Q U E S T I O N S 1. What is the common name of the compound CaOCl2? ? 2. Name the substance which on treatment with chlorine yields bleaching powder. 3. Name the sodium compound which is used for softening hard water. 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved. 5. Write an equation to show the reaction between Plaster of Paris and water. What you have learnt n Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases. n Acidic nature of a substance is due to the formation of H+(aq) ions in solution. Formation of OH–(aq) ions in solution is responsible for the basic nature of a substance. n When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed. n When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen. n When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water. n Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively. Acids, Bases and Salts 33 2024-25