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pH of a mixture of two weak acids - Nada - 04-12-2018
Hi!! I have a problem with one of the approximate formulas (for a mixture of two weak acids) which (it) derives from the expression: [H+]= ka_1/(Ka_1+ [H+]) *C_1 + ka_2/(Ka_2+ [H+])*C_2 At this point my textbook says that there are two main possible approximation: 1) If [H+]>Ka_1, Ka_2 : [H+]^2 = Ka_1*C_1 + Ka_2*C_2 2) If Ka_1>>Ka_2 and C_1 >(or equal) C_2 : [H+]= sqrt (Ka_1*C_1) My PROBLEM is to understand how i can arrive at the expression [H+]= sqrt (Ka_1*C_1) , using the assumptions Ka_1>>Ka_2 and C_1 >(or equal) C_2, starting from the expression: [H+]= ka_1/(Ka_1+ [H+]) *C_1 + ka_2/(Ka_2+ [H+])*C_2 Which are the mathematical-logical steps that i have to follow in order to get the approximate formula 2)??? Thanks very much!!!! |