Acids, Bases & Salts Class 10 ICSE PDF

ACIDS: The word ‘acid’ comes from the Latin word acidus, meaning ‘sour’. In fact, the sour taste of some foods is due to the acids they contain. Acids are defined as Compounds which contain one or more hydrogen atoms and when dissolved in water, produces hydronium ions (H3O+) the only positive charg...

ACIDS: The word ‘acid’ comes from the Latin word acidus, meaning ‘sour’. In fact, the sour taste of some foods is due to the acids they contain. Acids are defined as Compounds which contain one or more hydrogen atoms and when dissolved in water, produces hydronium ions (H3O+) the only positive charged ions. Classification of Acids 1. Depending on their sources i) Organic Acids-obtained from plants Ex. Acetic acid,Citric Acid. They are weak acid and forms ions and molecules in solution ii) Inorganic Acids-obtained from minerals Ex. Hydrochloric Acid.They are strong acids as they ionises completely 2. Depending on their concentration i) Concentrated acid-Amount of acid is more than amount of water. ii) Dilute acid-Amount of water is more than amount of acid 3. Depending on their basicity(No. of hydronium ions produced in complete ionisation) i) Monobasic acid- One hydronium ion Ex HCl, HBr ii) Dibasic acid-two Hydronium ions Ex. Sulphuric acid, iii) Tribasic acid- Three hydronium ions Ex. Phosphoric Acid Properties Of Acids i) Taste- Sour taste ii) Physical State- Solid Boric Acid. Liquid HCl. iii) Effect on skin-Corrosive action- Sulphric Acid (Black), HCl (Amber), Nitric Acid (Yellow) iv) They change the colours of indicators- Blue Litmus Red. Methyl orange to Pink. Phenolphthalein no change Those substances whose smell (or odour) changes in acidic or basic solutions are called OLFACTORY INDICATORS. For example, onion, vanilla and clove oil. Chemical Properties of Acids: i) Reaction with active metals- form Hydrogen and Metal Salt ii) Reaction with bases – Neutralisation iii) Reaction with carbonates and bicarbonates (hydrogen carbonates)- form Salt , water and Carbon di oxide iv) Reaction with sulphites and bisulphites- Forms salt , water and Sulphur dioxide. v) Reaction with sulphides- Salt and Hydrogen sulphides vi) Reaction with chlorides and nitrates- Only few (Ba, Pb) reacts with dil HCl rest ( Na, K) reacts only with Conc HCl. BASES: A base is either a metallic oxide or a metallic hydroxide or ammonium hydroxide which reacts with hydronium ions of an acid to form salt and water only. Basic Oxide: A basic oxide is a metallic oxide which contains the ion O2- and reacts with an acid to form salt and water only. Basic Hydroxide : It is a metallic hydroxide which contains OH- and will react with an acid to give salt and wate (b) A only. Alkalis: An alkali is a basic hydroxide which when b dissolved in water produces hydroxyl (OH-) ions as the only negatively charged ions. Classification of Bases: 1. On the basis of their strength i) Strong Base ii) Weak Base 2. On the basis of their acidity: i) Monoacidic Base ii) Diacidic Base iii) Triacidic Base Properties of Bases/Alkalis: Physical Properties:- i) They have a sharp and bitter taste. ii) They change the colour of indicators.- R-L-B, Mo-Yellow, CPh- Pink iii) They are soapy substances, i.e., they are slippery to touch. iv) They are strong electrolytes. Chemical properties:- i) Strong alkalis absorb carbon dioxide from the air to form carbonates. ii) They neutralise acids to form salt and water. iii) They precipitate as insoluble metallic hydroxides when added to the solutions of the salts of the heavy metals,Ex copper, iron, zinc, etc. iv) When alkalies are warmed with an ammonium salt, ammonia gas is given out. General Uses of Some Bases: Base Use 1. Sodium Manufacture of Hydroxide soaps 2. Potassium Manufacture of Hydroxide bleaching powder 3. Magnesia In making refractory bricks 4. Calcium Drying Agent, Oxide basic flux Strength of Acidic and Basic Solutions: The pH of a solution is the negative logarithm to the base 10 of the hydrogen ion concentration expressed in moles per litre.  The universal indicator is a mixture of indicator dyes that gives a spectrum of colours depending on how acidic or alkaline a solution is, Universal indicators gives different colours at different concentrations of hydrogen ions in a solution. SALTS: Salt is a compound formed by the partial or total replacement of the ionisable hydrogen atoms of an acid by a metallic ion or an ammonium ion. Classification of Salts: 1. Normal Salts: Normal salts are the salts formed by the complete replacement of the ionisable hydrogen atoms of an acid by a metallic or an ammonium ion. For example:- Hydrochloric acid yields sodium chloride, Sulphuric acid gives sodium sulphate. 2. Acid Salts: Acid salts are formed by the partial replacement of the ionisable hydrogen atoms of a polybasic acid by a metal or an ammonium ion. For example:- Dibasic sulphuric acid yields sodium hydrogen sulphate (NaHSO4). 3. Basic Salts: Basic salts are formed by the partial replacement of the hydroxyl group of a di- or a tri- acidic base by an acid radical. For example:- Basic lead chloride [Pb(OH)Cl], Basic Magnesium chloride [Mg(OH)CI]