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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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tony365 tony365
wrote...
Posts: 55
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11 years ago
The main Q was...0.10 mol of solid sodium hydrogen carbonate and 0.20 mol of solid sodium carbonate are dissolved in the same beaker of water, transferred to a volumetric flask and made to 250.0 mL. The Ka for HCO3 is 4.7e-11
its a buffer Q
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smn
wrote...
#1
11 years ago
Hi Lol,



HCO3(-) / CO3(2-) : . . . . . . . Ka = 4,7?10^-11

pKa = - log(Ka)
pKa = - log(4,7?10^-11)
pKa = 10,33

. . . before adding HCl :

pHo = pKa + log([CO3(2-)] / [HCO3(-)] )
pHo = pKa + log(0,20 / 0,10 )
pHo = 10,63


. . . after adding HCl :


pH = pKa + log( (0,20 - Ca?Va) / (0,10 + Ca?Va) )
pH = pKa + log( (0,20 - 0,050?20?10^-3) / (0,10 + 0,050?20?10^-3) )
pH = 10,62
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