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ICSE Notes for study of compounds

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Mira Sree
Lakshmi School, Veerapanchan, Madurai

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Study of compounds On a small scale, ammonia is obtained from ammonium salts, which decompose when treated with caustic soda or lime. It forms metal salt, water, and ammonia gas. Ammonia can also be prepared by treating metal nitrides with warm water. Properties of ammonia 1. It is a colourless gas with a pungent odour. 2. It is extremely soluble in water. 3. It is oxidised in excess of oxygen with and without catalyst. All soluble salts of metals react with aqueous ammonia to form their respective insoluble hydroxide and ammonium salts. Ammonia is used in the production of various nitrogen fertilisers (ammonium nitrate, urea, ammonium phosphate, and ammonium sulphate). Nitrates are the salts of nitric acid with metals. They are prepared by treating metals and metallic compounds with nitric acid. All nitrates decompose on heating. The products of decomposition depend on the type of nitrate i.e., whether it is a metal or non-metal. It liberates reddish brown fumes of nitrogen dioxide. Thus, it can be used as a test for nitrates. Alkali metal nitrates decompose on heating to form respective nitrites and oxygen while heavy metal nitrates decompose on heating to form respective metallic oxides, nitrogen dioxide, and oxygen. In laboratory, sulphur dioxide is prepared by treating sulphites of active metal with dilute sulphuric acid. It causes headache when inhaled in small amount while it might prove fatal in large amounts. It is a pungent smelling gas, which is soluble in water. It is heavier than air and its boiling point si 263 K. It is neither combustible nor does it support combustion. Also, it has both acidic and bleaching properties. It reacts with alkalis such as sodium hydroxide. When sulphur is present in limited amount, it forms their respective soluble sulphites and water, but when sulphur is present in excess amount, it forms their respective metal hydrogen sulphites. It reduces chlorine water to hydrochloric acid and forms sulphuryl chloride with dry chlorine gas. Moist sulphur dioxide behaves as a reducing agent. Concentrated sulphuric acid is known as oil of vitriol. It occurs in free state in hot water of sulphur springs. In combined state, it occurs as mineral sulphates. Sulphuric acid is prepared by contact process. It involves burning of a pure and dry mixture of two parts of sulphur or sulphide ores and one part of air in the presence of vanadium pentoxide or platinised asbestos as catalyst. Chemical reactions of H2SO4 are because of its 1. low volatility 2. strong acidic character 3. strong affinity for water 4. ability to act as an oxidising agent Dilute sulphuric acid reacts with active metals, metal oxides, metal hydroxides, metal carbonates, metal sulphites to form their respective metal sulphates and acid sulphates. Because of low volatility, it can be used for the manufacture of more volatile acids from their corresponding salts. It is a strong dehydrating agent. Because of its strong affinity for water, sulphuric acid removes water from hydrated salts and organic compounds. Concentrated sulphuric acid is a moderately strong oxidising agent and can oxidise both metals and non-metals. Hydrogen sulphide can be prepared by treating metal sulphides with sulphuric acid. It reacts with soluble salts of metals in both acidic and alkaline medium to form respective insoluble sulphides, which have a distinctive odour. Hence, it can be used in the detection of cation in an unknown salt. In laboratory, hydrogen chloride gas is prepared by heating sodium chloride with concentrated sulphuric acid. It is also prepared by burning hydrogen gas in the atmosphere of chlorine gas or by exposing hydrogen gas and chlorine gas to diffused sunlight. It is colourless and pungent-smelling with sour taste and a very irritating odour. It is extremely soluble in water. Hydrogen chloride is neither combustible nor does it support combustion. On heating at above 500 C, it dissociates into hydrogen and chlorine. On mixing with ammonia gas, it forms dense white fumes due to formation of ammonium chloride. Aqueous solution of hydrogen chloride is called hydrochloric acid. It is prepared by dissolving hydrogen chloride in water. It reacts with metals to form respective chlorides and hydrogen gas. Aqua regia is a mixture of 3 parts of concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a very corrosive acid and is the only known acid that can dissolve gold. Nitric acid It is prepared in laboratory by distilling equal parts of mixture of sodium nitrate or potassium nitrate with concentrated sulphuric acid. On a large scale, nitric acid is prepared by Ostwald s process. Nitric acid behaves as a strong acid in aqueous solution. Pure nitric acid is unstable towards heat and decomposes to form nitrogen dioxide. Metal oxides, hydroxides, carbonates, and hydrogen carbonates react with dilute nitric acid to form their respective soluble metallic nitrates. Nitric acid can oxidise most metals and non-metals. Nitrates are the salts of nitric acid with metals. They are prepared by treating metals and metallic compounds with nitric acid. All nitrates decompose on heating. The products of decomposition depend on the type of nitrate i.e., whether it is a metal or non-metal. It liberates reddish brown fumes of nitrogen dioxide. Thus, it can be used as a test for nitrates. Alkali metal nitrates decompose on heating to form respective nitrites and oxygen while heavy metal nitrates decompose on heating to form respective metallic oxides, nitrogen dioxide, and oxygen. The mole concept and stoichiometry 1 mole of any substance can be defined as: Amount of a substance that contains as many particles (atoms, molecules or ions) as there are atoms in 12 g of the 12C isotope Avogadro number or Avogadro constant (NA); equal to 6.022 1023 particles Percentage Composition Mass percent of an element =mass of the element in the compound/m.m of a compound. Empirical formula and molecular formula: Empirical formula Molecular formula Represents the simplest whole number ratio of various atoms present in a compound Represents the exact number of different types of atoms present in a molecule of a compound

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