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 P: 161 I missed this question on an exam and I was wondering if anyone can explain to me how to do it. 1. The problem statement, all variables and given/known data The pKa of acetic acid, HC2H3O2, is 4.76. A buffer solution was made using an unspecified amount of acetic acid and 0.300 moles of NaC2H3O2 in enough water to make 2 Liters of solution. Its pH was measured as 4.40 on a meter. How many moles of HC2H3O2 were used? 2. Relevant equations K= [products]/[reactions] pH= pKa + log (A/HA) 3. The attempt at a solution Ka= 10^(-4.76) = 1.74 x 10 ^(-5) Kb = 5.75 x 10^(-10) pH =4.4 [H]=3.98 x 10^(-5) pOH= 9.6 [OH]= 2.51 x 10^(-10) moles of OH= 2.51 x 10^(-10) x 2= 5.02 x 10^(-10) moles Base_________+____H2O -->___Acetic Acid_+_____OH +______Na .3 moles______________________x_________________0 -5.024 x 10^(-10)__________5.02 x 10^(-10)_______5.02 x 10^(-10) .2999 moles_______________x+ 5.02 x 10^(-10)______5.02 x 10^(-10) pH=pKa + log(A/HA) 4.4=4.76+ log (.3/(x+5.02 x 10^(-10))) =10^-(-.36)= 10^[log (.3/(x+5.02 x 10^(-10)))] 2.29= .3/(x+5.02 x 10^(-10))) (2.29)(x+5.02 x 10^(-10))=.3 x=.131 moles .3 + .131= 0.43 moles