The concentration of hydrogen ion is a measure of acidity or alkalinity of a solution. A convenient way of expressing the hydrogen ion concentration of a solution is, in terms of the pH scale devised by Sorenson's . The pH of a solutionis defined as the negative logarithm of active concentration of H^(+) ions to the base 10 i.e., pH =- log_(10)[HI^(+)] or [H^(+)]=10^(-pH) At 25^(@)C (i) if pH lt1 , then solution is acidic (ii) if pH=7, then solution is neutral (iii) if pH gt 7, then the solution is basic Total [H^(+)]and [OH^(-)] in a mixture of strong acids or bases are represented in terms normality, which is equal to final number of milliequivalents of H^(+) or OH^(-) present in millilitre of solution Since H_(2)O ionizes as H_(2)O hArrH^(+)+OH^(-) Ionic product of water , K_(w)=[H^(+)][OH^(-)] ...(i) Taking log on both sidesin equation (i), we find pH +pOH=pK_(w) For neutral solution, pH =pOH:. 2pH =pK_(w) :. pH =1.2pK_(w) Since dissociationof water is an endothermic process, so temperature willhave great effect on K_(w) as well as on the pH of solution i.e., the nature of the soluiton . K_(w) at different temperature are related as under. ln (K_(w2))/(K_(w1))=(DeltaH)/(R)[(1)/(T_(1))-(1)/(T_(2))] At T_(1)K=T_(2)K, K_(w_(2))=K_(w1) (i) pH mixture of monoprotic weak acid is calculated as under : pH of monoprotic weak acid i.e., CH_(3)COOH {:(,CH_(3)COOH,hArr,CH_(3)COO^(-),+,H^(+)),("at "t=0,C,,0,,0),("at "t=t,C-alpha,,C alpha,,Calpha):} :. K_(a)=(C alpha xx C alpha)/(C-Calpha)=(alpha^(2)C)/(1-alpha) When a le0.1 , 100 alpha =1-alpha=1 :. K_(a)=(alpha^(2)C)/(1) [When (1-alpha)=1] alpha=sqrt((K_(a))/(C)):. [H^(+)]=alphaC=sqrt(K_(a)xxC) (ii) pH of a mixture of monoprotic weak acids is calculated as follows [H^(+)]=sqrt(K_(a1)C_(1)+K_(a2)C_(2)). where K_(a1) and K_(a2) are dissociation constants of monoprotic weak acids HA and HB acid C_(1) and C_(2) are their concentrations respectively. (ii) pH of polyproticweak acid, say H_(3)A-a triprotic weak acid having dissociation constants K_(a1).K_(a2) and K_(a3) where K_(a1) gt gt K_(a2) gt gt K_(a3). Then in that case , maximum [H^(+)] will be contributed from step I, and neglibily small from concentration of species producing from step III will be negligible with respect to steop II and similarly concentration of species producig from step II will be negligible with respect to step I. Based upon the above discussion, answer the following questions. 2g NaOH is added to 100mL of M//20 H_(2)SO_(4) solution and the resulting solution is obtained by additino of 900 mL of wter, then what will be the pH of the solution ?