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Acids, Bases And Salts Indicators: Indicators are substances which indicate the acidic or basic nature of the solution by the colour change. Types of Indicator: There are many types of indicators. Some common types of indicators are: 1. Natural Indicators: Indic...

Acids, Bases And Salts Indicators: Indicators are substances which indicate the acidic or basic nature of the solution by the colour change. Types of Indicator: There are many types of indicators. Some common types of indicators are: 1. Natural Indicators: Indicators obtained from natural sources are called Natural Indicators. Litmus, turmeric, red cabbage, China rose, etc. Litmus: Litmus is obtained from lichens. The solution of litmus is purple in colour. Litmus paper comes in two colours- blue and red. An acid turns blue litmus paper red. A base turns red litmus paper blue. Turmeric: Turmeric is another natural indicator. Turmeric is yellow in colour. Turmeric solution or paper turns reddish brown with base. Turmeric does not change colour with acid. Red Cabbage: The juice of red cabbage is originally purple in colour. Juice of red cabbage turns reddish with acid and turns greenish with base. Acids: Acids are sour in taste, turn blue litmus red, and dissolve in water to release H+ ions. Example: Sulphuric acid (H2SO4), Acetic Acid (CH3COOH), Nitric Acid (HNO3) etc. Properties of Acids:  Acids have a sour taste.  Turns blue litmus red.  Acid solution conducts electricity.  Release H+ ions in aqueous solution. Types of Acids: Acids are divided into two types on the basis of their occurrence i.e., Natural acids and Mineral acids. (i) Natural Acids: Acids which are obtained from natural sources are called Natural Acids or Organic Acids. Examples: Methanoic acid (HCOOH) Acetic acid (CH3COOH) Oxalic acid (C2H2O4) etc. (ii) Mineral Acids: Acids that are prepared from minerals are known as Mineral Acids.Example; Inorganic acids, man- made acids or synthetic acid are also known as Mineral Acids. Example: Hydrochloric acid (HCl) Sulphuric acid (H2SO4) Chemical Properties of Acid: Reaction of acids with metal: Acids reacts with a metal give hydrogen gas along with respective salt Metal + Acid → Salt + Hydrogen Examples: Hydrogen gas and zinc chloride are formed when hydrochloric acid reacts with zinc metal. Hydrogen gas and sodium sulphate are formed when sulphuric acid reacts with sodium metal. Acids reacts with metal carbonates and Bicarbonates to produce salt, water and carbon dioxide gas. Hydrochloric acid reacts with sodium carbonate gives carbon dioxide gas, sodium chloride along with water When Sulphuric acid reacts with calcium carbonate gives calcium sulphate, carbon dioxide gas, and water. Nitric acid reacts with sodium carbonate gives sodium nitrate, water and carbon dioxide gas. Acids reacts with metal oxide to form salt and water. Metal oxide + Acid → Salt + Water Example: STRONG ACID: An acid which is completely ionised in water and thus produces a large amount of hydrogen ions is called a strong acid. WEEK ACID: An acid which is partially ionised in water and thus produces a small amount of hydrogen ions is called a weak acid. Bases: Bases are bitter in taste, have soapy touch, turn red litmus blue and give hydroxide ions (OH–) in aqueous solution. Examples: Sodium hydroxide (caustic soda) – NaOH Calcium hydroxide – Ca(OH)2 Potassium hydroxide (caustic potash) – (KOH) Properties of Bases:  Have a bitter taste.  Soapy to touch.  Turns red litmus blue.  Conducts electricity in solution.  Release OH– ions in Aqueous Solution  Strong Bases:  A base which completely ionises in water and thus produces a large amount of hydroxide ions (OH – ions) is called a strong base (or a strong alkali).  Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are strong bases Weak Bases  A base which is partially ionised in water and thus produces a small amount of hydroxide ions (OH– ions) is called a weak base  Ammonium hydroxide (NH4OH), calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2] are weak bases (or weak alkalis). Chemical properties of bases: Reaction of Base with Metals: When alkali (base) reacts with metal, it produces salt and hydrogen gas. Alkali + Metal → Salt + Hydrogen Examples: Sodium hydroxide gives hydrogen gas and sodium zincate when reacts with zinc metal. When sodium hydroxide reacts with aluminium metal Sodium aluminate and hydrogen gas are formed. Reaction of Base with Oxides of Non-metals: Bases react with non-metal oxides to form salt and water Reaction of Acid with Metal Oxides: When an acid reacts with a metal oxide salt and water are formed. Acid + Metal Oxide → Salt + Water Examples: STRENGTH OF ACID AND BASE SOLUTIONS : pH SCALE  The pH of a solution is inversely proportional to the concentration of hydrogen ions in it. That is, a solution having a high concentration of hydrogen ions has a low pH value. On the other hand, a solution having low concentration of hydrogen ions has a high pH value  In the term pH, letter ‘p’ stands for a German word ‘potenz’ which means ‘power’ and letter H stands for hydrogen ion concentration [H+].  According to the rules of pH scale :  SALTS A salt is a compound formed when the hydrogen of an acid is replaced by a metal. Salts are electrically neutral. There are number of salts but sodium chloride is the most common among them. Sodium chloride is also known as table salt or common salt. Characteristics of salt:  Most of the salts are crystalline solid.  Salts may be transparent or opaque.  Most of the salts are soluble in water.  Solution of the salts conducts electricity in their molten state also.  The salt may be salty, sour, sweet and bitter.  Neutral salts are odourless.  Salts can be colourless or coloured. Family of Salts Family of Salt: Salts having common acidic or basic radicals are said to belong to the same family. Example: (i) Sodium chloride (NaCl) and Calcium chloride (CaCl2) belongs to chloride family. (ii) Calcium chloride (CaCl2) and Calcium sulphate (CaSO4) belongs to calcium family. (iii) Zinc chloride (ZnCl2) and Zinc sulphate (ZnSO4) belongs to the zinc family. Neutral, Acidic and Basic Salts: (i) Neutral Salt: Salts produced because of reaction between a strong acid and strong base are neutral in nature. The pH value of such salts is equal to 7, i.e. neutral. Example : Sodium chloride, Sodium sulphate. Postassium chloride, etc. Sodium chloride (NaCl): It is formed after the reaction between hydrochloric acid (a strong acid) and sodium hydroxide (a strong base). (ii) Acidic Salts: Salts which are formed after the reaction between a strong acid and weak base are called Acidic salts. The pH value of acidic salt is lower than 7. For example Ammonium sulphate, Ammonium chloride, etc. Ammonium chloride is formed after reaction between hydrochloric acid (a strong acid) and ammonium hydroxide (a weak base). (iii) Basic Salts: Salts which are formed after the reaction between a weak acid and strong base are called Basic Salts. For example; Sodium carbonate, Sodium acetate, etc. Sodium carbonate is formed after the reaction between sodium hydroxide (a strong base) and carbonic acid (a weak acid). COMMON SALT (SODIUM CHLORIDE) Common salt is also known as just ‘salt’. The chemical name of common salt is sodium chloride (NaCl). How Common Salt is Obtained Common salt occurs in dissolved form in sea-water. On the other hand, common salt occurs in solid form as rock salt. (i) Common Salt from Sea-Water. Sea-water contains many dissolved salts in it. The major salt present in sea-water is common salt (or sodium chloride). Common salt is obtained from sea-water by the process of evaporation. (ii) Common Salt from Underground Deposits The large crystals of common salt found in underground deposits are called rock salt. Rock salt is usually brown due to the presence of impurities in it. Uses of Common Salt (or Sodium Chloride) Some of the important uses of common salt (or sodium chloride) are given below. 1. It is used as a raw material for making a large number of useful chemicals in industry such as : sodium hydroxide (caustic soda), sodium carbonate (washing soda), sodium hydrogen carbonate (baking soda), hydrochloric acid, hydrogen, chlorine, and sodium metal. 2. It is used in cooking food. It improves the flavor of food. Sodium chloride is required by our body for the working of nervous system, the movement of muscles, and the production of hydrochloric acid in the stomach for the digestion of food. 3. It is used as a preservative in pickles, and in curing meat and fish (preserving meat and fish). CHEMICALS FROM COMMON SALT 1. SODIUM HYDROXIDE: Sodium hydroxide is commonly known as caustic soda. The chemical formula of sodium hydroxide is NaOH. Production of Sodium Hydroxide: Sodium hydroxide is produced by the electrolysis of a concentrated aqueous solution of sodium chloride (which is called brine). When electricity is passed through a concentrated solution of sodium chloride (called brine), it decomposes to form sodium hydroxide, chlorine and hydrogen   During electrolysis, chlorine gas is produced at the anode (positive electrode) and hydrogen gas is produced at the cathode (negative electrode). Sodium hydroxide solution is formed near the cathode.  Uses of Sodium Hydroxide: 1. Sodium hydroxide is used for making soaps and detergents. 2. Sodium hydroxide is used for making artificial textile fibres (such as rayon). 3. Sodium hydroxide is used in the manufacture of paper. 2. WASHING SODA:  Washing soda is sodium carbonate containing 10 molecules of water of crystallizations. Washing soda is sodium carbonate decahydrate. The formula of washing soda is Na2CO3.10H2O.  Anhydrous sodium carbonate (Na2CO3) is commonly known as ‘soda ash’. Uses of Sodium Hydrogencarbonate (or Baking Soda) 1. Sodium Hydrogencarbonate is used as an antacid in medicine to remove acidity of the stomach. 2. Sodium Hydrogencarbonate (or baking soda) is used in making baking powder (used in making cakes, bread, etc.). Baking powder is a mixture of baking soda (sodium hydrogen carbonate) and a mild, edible acid such as tartaric acid. When baking powder mixes with water (present in dough made for baking cake or bread), then sodium Hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas. The carbon dioxide gas produced gets trapped in the wet dough and bubbles out slowly making the Cake (or bread) to ‘rise’ and become soft and spongy 3. Sodium Hydrogencarbonate (or baking soda) is used in soda-Acid fire extinguishers. 4. BLEACHING POWDER: Bleaching powder is calcium oxychloride. The chemical formula of bleaching powder is CaOCl 2. It is also called chloride of lime. Preparation of Bleaching Powder Bleaching powder is prepared by passing chlorine gas over dry slaked lime. Uses of Bleaching Powder 1. Bleaching powder is used for bleaching (To remove any colour present) cotton and linen in textile industry and for bleaching wood pulp in paper industry. It is also used for bleaching washed clothes in laundry. 2. Bleaching powder is used for disinfecting drinking water supply. That is, for making drinking water free from germs. 3. Bleaching powder is used for the manufacture of chloroform (CHCl3). 4. Bleaching powder is used as an oxidising agent in many chemical industries. 5. PLASTER OF PARIS: Plaster of Paris is calcium sulphate hemihydrate (calcium sulphate half-hydrate). The formula of plaster of Paris is CaSO4. ½ H2O.  The name plaster of Paris came from the fact that it was first of all made by heating gypsum which was mainly found in Paris.  Plaster of Paris is commonly known as P.O.P. Preparation of Plaster of Paris Plaster of Paris is prepared by heating gypsum (CaSO4.2H2O) to a temperature of 100°C (373 K) in a kiln. When gypsum is heated to a temperature of 100°C (373 K) , it loses three-fourths of its water of crystallisation and forms plaster of Paris. The temperature during the heating of gypsum should not be allowed to go above 100°C (or above 373 K). This is because if gypsum is heated above 100°C (or above 373 K), then all its water of crystallisation is eliminated and anhydrous calcium sulphate (CaSO4) called dead burnt plaster is formed. The anhydrous calcium sulphate (or dead burnt plaster) does not set like plaster of Paris on adding water. Uses of Plaster of Paris 1. Plaster of Paris is used in hospitals for setting fractured bones in the right position to ensure correct healing. when added with water the P.O.P became a hard mass to makes the broken part immovable. 2. Plaster of Paris is used in making toys, decorative materials, cheap ornaments, cosmetics, black-board chalk and casts for statues. 3. Plaster of Paris is used as a fire-proofing material. 4. Plaster of Paris is used in chemistry laboratories for sealing air-gaps in apparatus where air-tight arrangement is required. 5. Plaster of Paris is used for making surfaces (like the walls of a house) smooth before painting them, and for making ornamental designs on the ceilings of houses and other buildings.