10.36 is the ph of a solution made by dissolving 1.9 g of k2co3 and 7.9 g of khco3 in 500. ml of water
Mass of K2CO3 = 1.9 g
Moles of K2CO3 = ( Mass / Molar mass ) = ( 1.9 g / 138.205 g / mol ) = 0.031 mol
Mass of KHCO3 = 7.9 g
Moles of KHCO3 = ( Mass / Molar mass ) = ( 7.9 g / 100.115 g / mol ) = 0.0789 mol
Volume of solution = 500 mL = 0.5 L
[ HCO3- ] = 0.078 mol / 0.5 L = 0.156 M
[ CO32-] = 0.031 mol / 0.5 L = 0.062 M
Ka for HCO3- = 4.7 x 10 -11
pKa = 10.32
pH = pKa + log [CO32-] / [HCO3-]
pH = 10.32 + log ( 0.062/0.156 ) = 10.32 - 0.4 = 10.31
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