Title Chapter 2 Acids Bases and Salts.pdf ✅

SCIENCE (Chemistry) Chapter 2: Acids, Bases & Salts
(1) 02 ACIDS, BASES AND SALTS Acids, Bases & Salts Three different theories have been put forth in order to define acids and bases. ● The Arrhenius theory of acids and bases states that “an acid generates H+ ions in a solution whereas a base produces an OH– ion in its solution”. ● The Bronsted-Lowry theory defines “an acid as a proton donor and a base as a proton acceptor”. ● Finally, the Lewis definition of acids and bases describes “acids as electron-pair acceptors and bases as electron-pair donors”. Acids and Bases in the Laboratory Indicators An indicator tells us whether a substance is acidic or basic in nature, by the change in colour. Common Indicators ● An acid turns blue litmus red and a base turns red litmus blue. ● Methyl orange indicator gives a red colour in an acidic solution and gives a yellow colour in a basic solution. ● Phenolphthalein is colourless in an acidic solution and gives a pink colour in a basic solution. Olfactory Indicators ● Those substances whose odour changes in acidic or basic media are called olfactory indicators. For example: onion, vanilla and clove oil. ● On adding sodium hydroxide solution to a cloth strip treated with onion, the smell of the onion is not detected. An acidic solution does not eliminate the smell of the onion. Reaction of Acids & Bases with Metals Acids react with metals to produce salt by displacing hydrogen.
(2) 02 ACIDS, BASES AND SALTS For Example: 1. When dilute sulphuric acid reacts with the metal zinc, zinc sulphate is formed with the evolution of hydrogen gas. Zn + H2SO4 → ZnSO4 + H2 2. Zinc is the only metal which reacts with sodium hydroxide to form sodium zincate with the release of hydrogen gas. Zn + 2NaOH → Na2ZnO2 + H2 Reaction of zinc granules with dilute sulphuric acid and testing hydrogen gas by burning Reaction of Metal Carbonates & Bicarbonates with Acids Acids react with metal carbonates or bicarbonates to form salt and water with the evolution of carbon dioxide gas. For Example: 1. Hydrochloric acid reacts with sodium carbonate to form sodium chloride and water with the release of carbon dioxide gas. Na2CO3(s) + 2 HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l) 2. Similarly, sodium bicarbonate also reacts with hydrochloric acid to form sodium chloride and water with the release of carbon dioxide gas. NaHCO3(s) + HCl (aq) → NaCl (aq) + CO2(g) + H2O(l)
(3) 02 ACIDS, BASES AND SALTS Passing carbon dioxide gas through calcium hydroxide solution Acids and Bases React with each other The reaction between an acid and a base to form salt and water is called a neutralisation reaction. For example: Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l) In general, a neutralisation reaction can be written as: Base + Acid → Salt + Water Reaction of Metallic Oxides with Acids Acids react with metallic oxides to form salt and water. For Example: Copper oxide (II), a black metal oxide reacts with dilute hydrochloric acid to form a blue- green coloured copper chloride (II) solution. CuO + 2HCl → CuCl2(aq) + H2O Reaction of Non-Metallic Oxides with Base Bases react with non-metallic oxides to form salt and water. For Example: Calcium hydroxide reacts with non-metallic oxides like carbon dioxide to form calcium carbonate salt and water. Ca(OH)2 + CO2 → CaCO3 + H2O Acids and Bases in Water Acids An acid is a substance which dissociates (or ionises) when dissolved in water to release hydrogen ions.