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Balance the following skeleton equation by the method of Partial Equations : P+HNO_(3)rarr H_(3)PO_(4)+H_(2)O+NO_(2). |
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Answer» Solution :This reaction is involves oxidation of phosphorus by nitric acid and takes place in the following steps : (i) Nitric acid decomposes to liberate nascent oxygen. `2HNO_(3)rarr 2NO_(2)+H_(2)O+(O)"…(1)"` (ii) Nascent oxygen oxidises phosphorus to phosphorus pentoxide. `2P+5(O)rarr P_(2)O_(5)"...(2)"` (iii) Phosphorus pentoxide, `P_(2)O_(5)`, dissolves in water to produce phosphoric acid. `P_(2)O_(5)+3H_(2)Orarr 2H_(3)PO_(4)"...(3)"` (iv) To cancel the intermediate products, multiply the partial EQUATION (1) by 5 and adding to eqns. (2) and (3), we have `10HNO_(3)+2Prarr 2H_(3)PO_(4)+2H_(2)O+10NO_(2)` Dividing by the common factor 2, we have `5HNO_(3)+Prarr H_(3)PO_(4)+H_(2)O+5NO_(2)` This represents the ATOMIC equation since phosphorus which is known to exist in the molecular form `(P_(4))` has been written in the atomic form. (V) To make the above atomic equaiton molecular, multiply it throughout by 4. Thus, we have the required balanced molecular equaiton : `20HNO_(3)+P_(4)rarr 4H_(3)PO_(4)+4H_(2)O+20NO_(2)` |
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