Sparkling mineral water at 25 °C contains 0.033 M H₂CO₃(aq) from dissolved CO₂ and 0.010 M Ca²⁺. Given Ka1(H₂CO₃)=4.3×10−7, Ka2(H₂CO₃)=5.6×10−11, and Ksp(CaCO₃)=4.8×10−9, at what pH will CaCO₃(s) just begin to precipitate from the solution?
a) 8.4
b) 4.9
c) 5.9
d) 10.1