You dissolve 2.35 g of sodium carbonate (Na2CO3) in sufficient water to produce a final solution volume of 100.0 mL. Assuming all of the solid dissolves, calculate the solution pH.
mols Na2CO3 = grams/molar mass = about 2.35/106 = about 0.02 but you need a better answer than that.
M Na2CO3 = mols/L = about 0.02/0.1L = about 0.2 M
....CO3^2- + H2O ==> HCO3^- + OH^-
I...0.2...............0.......0
C...-x................x.......x
E..0.2-x..............x.......x
Kb1 for CO3 = (Kw/k2 for H2CO3) = (x)(x)/(0.2-x).
Solve for x = (OH^-) and convert to pH.