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| Preparation of Acids |
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| Some acids can be prepared by the direct combination of a non-metal with hydrogen. For e.g., |
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| In the above reactions, the obtained gases like hydrogen chloride, hydrogen iodide and hydrogen sulphide are also called the acid anhydrides. They exhibit acidic properties, only when dissolved in water.Therefore an acid anhydride is a substance that dissolves in water to form an acid. In other words, it is the acid minus water (acid - water = acid anhydride). |
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| Examples: CO2 gas is the acid anhydride of carbonic acid, SO3 gas is the acid anhydride of carbonic acid, HCl gas is the acid anhydride of hydrochloric acid. |
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| Oxides that can add on hydrogen ions to their molecules are called acidic oxides. Thus when they dissolve in water they associate with hydrogen ions to form acids. |
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| The hydrogen ions of less volatile acids, like concentrated sulphuric acid, can help displace metal ions of salts of volatile acids, to produce the acid. |
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| Hydrogen sulphide is the acid anhydride. |
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| Non metals like sulphur, phosphorous get oxidized by concentrated nitric acid to form their respective acids. |
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