Trista Nigh

A 5.55g sample of a weak acid with Ka=1.3 x10^-4 was combined with 5.00 mL of 6.00 M NaOH and the resulting solution was diluted to 750 mL. The measured pH of the solution was 4.25. What is the molar mass of the weak acid?

One of the main components of hard water is CaCO3. When hard water evaporates, some of the CaCO3 is left behind as a white mineral deposit. If hard water solution is saturated with calcium carbonate, what volume of the solution has to evaporate to deposit...

I took the square root of (4.96x10^-9)= 7.04x10^-5 mol/L then 100.09g/mol x 7.04 mol/L= 7.05x 10^-3 g/L then .100 g x 1 L/ 7.05x10^-3= 7.05x10^-4 L, so that was my final answer, does this seem right?