Title 3 Study of Acids, Bases and Salts.pdf ✅

Study of Acids, Bases and Salts Acids Acids are substances having a sour taste. The word ‘acid’ comes from a Latin word ‘acidous’, which means sour. Classification of Acids: • Based on the source: Organic acids: Orange, tamarind, raw mango, etc. are sour in taste. Therefore, these contain substances that are acidic in nature. Such acids are known as organic acids. These acids are found in plants. Carbon atoms are also present in such acids besides hydrogen atoms. The given table lists some organic acids. Acid Substance Acetic acid Vinegar Citric acid Lemon, orange Tartaric acid Tamarind, grapes Ascorbic acid (Vitamin C) All citrus fruits Lactic acid Milk, yoghurt Malic acid Apple and Pear Formic acid Ant Sting Mineral/Inorganic acids: These are inorganic acids and are obtained from minerals. Therefore, these acids are called mineral acids. These are acids that dissociate to give a proton. Carbon atoms are not present in such acids. Some examples of mineral acids are given in the following table. Hydrochloric acid HCl Nitric acid HNO3
Sulphuric acid H2SO4 Sulphurous acid H2SO3 Carbonic acid H2CO3 When HCl is added to water, it gives H+ and Cl− ions. The chemical equation for the process is: Similarly, sulphuric acid gives two protons and one sulphate ion. Inorganic acids are strong acids. They undergo complete ionisation in solution. There are few acids containing oxygen atoms too, these are called oxy-acids. For example, sulphuric acid (H2SO4), nitric acid (HNO3), etc. • Based on concentration: Concentration defines the amount of an acid present in a given amount of aqueous solution of the acid. Based on concentration acids are divided as: Concentrated acid: Those acids that have very less amount of water are known as concentrated acids. Dilute acid: Those acids that have a larger amount of water are known as dilute acids. Concentrates acids can be diluted by adding them slowly to water with constant stirring. One should never add water to acid, as it is an exothermic process. A large amount of heat being released causes the acid to spill out. • Based on basicity: Basicity of an acid: It can be defined by the number of hydrogen ions furnished by a molecule of an acid in an aqueous solution. You can observe in the above equations that one molecule of hydrochloric acid gives only one proton whereas one molecule of sulphuric acid gives two protons. Depending upon the number of protons furnished, the acids have been classified into three types.
• Monobasic acids: They have only one replaceable hydrogen atom. For example, HCl • Dibasic acids: They have two replaceable hydrogen atoms. For example, H2SO4 • Tribasic acids: They have three replaceable hydrogen atoms. For example, H3PO4 Preparation of Acids Acids can be prepared in many ways. The most common methods of obtaining acids are discussed below. • By combining an oxide of a non-metal with water We know that elements combine with oxygen to form oxides. When oxides of non- metals react with water, acids are obtained. SO2 + H2O → H2SO3 CO2 + H2O → H2CO3 N2O5 + H2O → HNO3 This method is used to prepare oxy-acids only. • By reaction of sulphuric acid with salts Sulphuric acid reacts with various salts to give various acids. 2 NaCl + H2SO4 → Na2SO4 + 2 HCl 2 NaNO3 + H2SO4 → Na2SO4 + 2 HNO3 • By direct combination (synthesis) Hydrogen combines directly with non-metals like chlorine, bromine etc. to form binary (two elements) acids. H2 + Cl2 → 2 HCl • By oxidation of non-metals Non-metals are oxidised to form acids with concentrated nitric acid. S + 6 HNO3 → H2SO4 + 2 H2O + 6 NO2 P + 5 HNO3 → H3PO4 + H2O + 5 NO2
Physical Properties Various physical properties of acids are given below. • Acids are sour to taste. • They exist as solids or liquids at room temperature. • They have a pH value less than 7. • They are soluble in water. • They are good conductors of electricity. • Strong mineral acids are corrosive in nature and can cause painful burns on the skin. Chemical properties Reaction of acids with metals Metals react with acids to form salts and hydrogen gas. We know that acids contain hydrogen atom(s). Metals replace these hydrogen atoms to form metal salts and hydrogen gas. As metal atoms replace hydrogen atoms, these reactions are examples of displacement reactions. Reaction of acids with metal oxides Acids react with metal oxides such as copper oxide, zinc oxide, etc. to produce metal salts. The reaction between a metal oxide and an acid can be written as: For example, HCl reacts with copper oxide (CuO) to produce a metal salt i.e., copper chloride and water. It is observed that copper chloride dissolves in water and forms a solution that is blue-green in colour. Reaction of acids with metal carbonates