Question

What is the pH of a solution prepared by adding 0.2g of Na2CO3 and 0.2g of NaHCO3 to water and bringing to a volume of 1liter? (pKa2=10.25)

Answer 1

Moles of $Na_2CO_3=$ $0.2g\over 105.99g/mol$ $=0.00199moles$

Molarity=$0.00199moles\over 1L$ $U=1.90\times 10^{-3} M$

Moles of $NaHCO_3=$ $0.2g\over 84.007g/mol$ $0.00239moles$

Molarity of $=$ $0.00239moles\over 1L$ $=2.39\times 10^{-3} M$

$pH=pKa_2+log[HCO_3^{2-}/pCO-2]$

$pH=10.25+log2.39\times 10^{-3}$

$pH=10.25+(-0.924)=9.32$