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Give preparation and properties of carbon dioxide. |
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Answer» Solution :Preparation : It is prepared by complete combustion of carbon and carbon containing fuels in excess of air. `C_((s)) + O_(2(g)) oversetDeltato CO_(2(g))` `CH_(4(g)) + 2O_(2(g)) oversetDeltato CO_(2(g)) + 2H_2O_((g))` In the laboratory it is conveniently prepared by the action of dilute HCl on calcium carbonate. `CaCO_3 + 2HCl toCaCl_2+ CO_2 + H_2O` On commercial scale `CO_2` is obtained by heating limestone and ethenol. `CaCO_(3) underset"1600 K"oversetDeltato underset"Limestone"(CaO+CO_2)` `C_6H_12O_6 underset"Enzyme"overset"Zymes"to underset"Ethyl alcohol"(2C_2H_5OH)+2CO_2` Properties : (i) It is colourless, odourless gas and about 1.5 times heavier than air. (II) It is not poisonous but it does not support life of animal and human being but they die in its presence due to lack of `O_2` gas. (iii) At room temperature and 50 to 60 atm. pressure `CO_2` gas can be liquefied, when LIQUID `CO_2` is allowed to evaporate rapidly i.e. expands rapidly, it is converted into SOLID which is known as dry ice. (iv) `CO_2` gas is neither combustible nor SUPPORTER of combustion. However, in its presence certain active metals such as Na, K, Mg etc. continue to burn. `2Mg+CO_2 to 2MgO + C` (v) `CO_2` turns blue litmus paper red so it is acidic in nature. (vi) It is sparingly soluble in water but when dissolved in water, carbonic acid (soda water `H_2CO_3`) can be obtained which is dibasic acid and it dissociates in two stages. `H_2CO_3 + H_2O hArr HCO_(3)^(-) + H_3O^(+)` `HCO_3^(-) + H_2O hArr CO_3^(-2) + H_3O^+` (vii) On passing `CO_2` through lime water it turns milky due to formation of insoluble `CaCO_3` and on passing it in excess milkiness disappears due to formation of soluble calcium hydrogen carbonate (calcium bicarbonate) `underset"Lime water"(Ca(OH)_2) +CO_2 to underset"Insoluble"(CaCO_3) + H_2O` `CaCO_3 + CO_2 + H_2O to underset"Calcium hydrogen carbonate"(Ca(HCO_3)_2)` (viii)In the presence of sunlight and chlorophyll of green plants, `CO_2` reacts with water to form glucose. This reaction is called photosynthesis. `6CO_2 + 6H_2O underset"Chlorophyll"overset"hv"to C_6H_12O_6+6O_2 + 6H_2O` |
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