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| Summary |
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 Strength of an acid depends on the concentration of hydronium ions present in a solution. Greater the numbers of hydronium ions present, greater is the strength of the acid. |
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A strong acid dissociates completely in water. |
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| Example: Hydrochloric acid |
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A weak acid dissociates only partially when dissolved in water. |
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| Example: Acetic acid |
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Basicity of an acid is the number of replaceable hydrogen ions in it. HCl is Monobasic and H2SO4 is Dibasic. |
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Acids are prepared by |
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| - direct combination of elements. |
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| - dissolving acidic oxide in water. |
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| - displacement of metal ions from salts. |
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| - action of dilute acids on salts. |
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| - the oxidation of non metals with concentrated nitric acid. |
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Acids react with metals like Mg, Zn, Fe to give salt and hydrogen. |
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Acids react with basic hydroxides, carbonates, sulphites and sulphides to give salt and a volatile gas such as carbon dioxide, sulphur dioxide and hydrogen sulphide as the case may be. |
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Strength of a base depends on the concentration of hydroxyl ions. |
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A strong base dissociates completely in water. |
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| Example: Sodium hydroxide |
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A weak base dissociates partially in water. |
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| Example: Ammonium hydroxide |
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The acidity of a base is equal to the number of hydroxyl ions it has. Monoacidic base- NaOH, diacidic base- Ca(OH)2. |
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Bases are prepared by |
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| - direct combination of metal and oxygen. |
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| - thermal decomposition of carbonates or metal nitrates. |
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| - double decomposition. |
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| - the action of active metals or basic oxides in water. |
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Some hydroxides, like that of zinc, lead and aluminium, are only weakly basic. Therefore they react |
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| - with acids to form salt and water. |
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| - with strong alkalies to form salt and water. |
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| These hydroxides are said to exhibit amphoteric behaviour. |
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According to modern concept an acid is a proton donor and a base is proton acceptor. |
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The strength of an acid or base is expressed on a 14 point scale (ranges from 0 to 14) known as pH Scale. |
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Water of crystallization is the number of molecules chemically combined in a definite molecular proportion with the salt in the crystalline state. This water is responsible for the geometric shape and colour of the crystals. Certain salts contain water of crystallization as part of the molecule. |
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| Example: Washing soda crystals or sodium carbonate decahydrate, Na2CO3.10H2O |
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Hygroscopic substances are substances, which absorb moisture from the air. Example: Sodium hydroxide |
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Certain hygroscopic substances not only absorb moisture from the air, but dissolve themselves in the moisture, undergoing a change of state. Such substances are called deliquescent substances. |
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| Example: CaCl2. |
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