1. The problem statement, all variables and given/known data 1) A 0.682-gram sample of an unknown weak monoprotic organic acid, HA, was dissolved in sufficient water to make 50 milliliters of solution and was titrated with a 0.135-molar NaOH solution. After the addition of 10.6 milliliters of base, a pH of 5.65 was recorded. The equivalence point (end point) was reached after the addition of 27.4 milliliters of the 0.135-molar NaOH. (a) Calculate the number of moles of acid in the original sample. Done. 3.70 * 10^-3 mol HA (b) Calculate the molecular weight of the acid HA. Done. 184.37 g/mol (c) Calc the number of moles of unreacted HA remaining in solution when the pH was 5.65. done. 0.0027 mol (d) Calculate the [H3O+] at pH = 5.65. done. 2.2 * 10^-6 (e) Calculate the value of the ionization constant, Ka, of the acid HA. I am using an ICE chart, with the equation HA <-> H+ + A- The initial concentration for HA I used was 0.0027 mol/ 0.050 L the initial concentration for H+ was 2.2 * 10 ^-6, which is also equal to the concentration of A-. However, when I plug in these values into the equilibrium expression, Ka = ([H+][A-])/[HA], I get 1.1 * 10^ -10, and the answer key says that the correct answer is 1.4 * 10 ^-6. Am I doing something wrong here, or is the answer key wrong?