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The CompoundM-O-H canactbothas anacid orbasedependinguponthe ionizationenthalpyofthe elementM. Justify by takingelements(M) of the thirdperiodof the periodic table . |
Answer» Solution :If theionizationenthalpy of theelements M islow it has astrongtendencyto getoxidisedto `M^(+)` . As aresult the M-OHbond willbreakto produce `M^(+)` and `OH^(-)` ions andhencethe compoundM-OHactsas a base  Furtherlower theionizationenthalpy of THEELEMENT (M) , stronger is the basic strength of thecompound M-O-H.Sincein generalionizationenthalpyincreases fromleftto rightin aperiodthereforebasiccharacterdecreasesin the sameorder. ThusNaOHis thestrongest basicfollowedby Mg `(OH)_(2)` while`A1(OH)_(3)`is theweakestbase. Infact`A1(OH)_(3)`is AMPHOTERICIN character. On theotherhandif theionizationenthalpyof the elementsM is high is haslittletendency ofgetconvertedinto `M^(+)` ion. Insteadthe compoundM-OH ionizationto produce `H^(+)` ionsand hencethe compoundM-O-H behavesas an acid.  Furtherhigher the IONIZATIONENTHALPY of theelement (M), stronger isthe acidicstrengthof the compound M-O-H.Sincein generalionizationenthalpyincreasesfrom lefttorightin aperiod acidiccharacterincreasesin thesameorder. forexample`Si(OH)_(4) " or" H_(2) SiO_(3)` is the weakestacid O=`P(OH)_(3)" or" H_(3) PO_(4)` is astronger acidthan `H_(2) SiO_(3), O_(2) S(OH)_(2)" or" H_(2)SO_(4)` is amoderratelystrong acidwhile`O_(3) CI(OH)` or `HC1O_(4)` is thestrongest acid . Thusfrom theabovediscussionit follows that as theionizationenthalpy of the element (M)increases from left to rightin a periodthe basiccharacterof thecompoundMOHdecreases whilethe acidic characterincreases. |
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