Can anyone he lp...a chemistry question?

Question

I have a question. How to find moles of Hcl in a solution.... A 1L soln having NaC3H5O3 has initial concentration of 0.1M. An unkown no. of moles of Hcl is then added to bring the final solution to a PH of 3.77. How many moles of Hcl were added? What is the common name of this type of problem?

Answer 1

OKay, I think you start with a base but when you add the HCl it becomes as acid. Since you have the pH you can find the concentration of the H+, which is -log(3.77) = 0.000169824 M. If you look up the value of Ka for this reaction you can find the equilibrium concentration of C3H5O3- and if you subtract 0.1M from this concentration and multiply by 1 liter you can find the moles of HCl added...I think. I'm no expect though.

So you start with a salt that completely dissociates in solution

NaC3H5O3 --> Na+ + C3H5O3-

Then water reacts with the C3H5O3-

C3H5O3- + H2O <--->  HC3H5O3 + OH-

Then you add HCl, another source of H+ and I think* I would react with OH- to give water and then the water would act as a base and accept H+ from HC3H5O3 to give the solution pH 3.77

HC3H5O3 + H2O <--> H3O+ C3H5O3-

I'm just learning this stuff myself so I hope someone smarter comes along and checks it.