quantitative chemical analysis essay writing services

in the attached file there is a questions that need to be answered with details of the solutions … if you have any questions emil me please I hope that you can do it, let me know ASAP thanks here is the questions

1. You are handed a beaker containing 50.0 mL of a solution of phenylalanine in water. You begin to titrate the phenylalanine with 0.0500 M HNO3 while monitoring the pH of the solution. Upon addition of 15.25 mL of 0.0500 M HNO3 you notice a large change (decrease) in the pH of the solution (i.e. an endpoint). You continue to add an additional 4.75 ml of the 0.0500 M HNO3. You then backtitrate the sample with 0.0615 M NaOH. Upon addition of 3.86 mL of the base you notice a large increase in the pH of the solution (i.e. an endpoint) and upon addition of a total of 17.85 ml of the base you notic a second large increase in the pH (i.e. an endpoint).
a) Calculate the initial concentration of the phenylalanine solution.
b) Calculate the pH of the original solution (before any titrations are done)? (You should recognize that your original solution was somewhere between the 1st and 2nd equivalence point.) (pK1 = 2.20 and pK2 = 9.31 for phenylalanine)
c) What is the pH of the solution at the equivalence point of the acid titration?
d) What is the pH of the solution at the 2nd equivalence point of the base titration?

2. Consider BaF2. This compound is a slightly soluble solid (Ksp = 1.7 x 10-6) for which one of the dissociation products is the conjugate base of a weak acid (Ka(HF) = 6.8 x 10-4).
a) Solve for the concentration of Ba2+ and F- by neglecting the influence of the acid-base equilibria and by assuming that all activity coefficients = 1.
b) Use the systematic treatment of equilibria to set up the equations to calculate the [Ba2+], [F-], [HF], [H+] and [OH-] by accounting for all of the interacting equilibria.
c) Use a spreadsheet to arrive at a convergent solution to the derived equations that allows the activity coefficients and equilibrium constants to be entered as variables. Solve for the equilibrium concentrations of all species in solution first by assuming that all γ = 1.
d) Use the calculated ion concentrations to determine approximate values for the γ’s for each of the species in solution. Enter these values and resolve for the equilibrium concentrations of all species in solution. Repeat this process until the solution converges (less than 0.1% change in concentrations).
e) By how much (relative percent error) is your initial approximate answer in error as compared with the value calculated using the spreadsheet.

3. As discussed in class use the systematic treatment of equilibria to derive an equation in [H+] for the titration of a weak acid, HA, with NaOH. However, in your derivation be sure to include the appropriate activity coefficients for the ionic species in solution.

a) Using the equation you’ve derived set up a spreadsheet that calculates the concentrations of all ions in solution for a monoprotic acid as a function of added titrant and plots the pH versus volume titration curve. To do this you should set up cells where you can input the initial concentration of HA, the NaOH concentration, the activity coefficients for the ionic species, the initial volume of the HA and the Ka for HA. Next, input the appropriate formulas to calculate the formal Na+ and HA concentrations as a function of the volume of added titrant. You will then have to input the appropriate formulae to solve the cubic equation derived in the handout to determine the [H+] and pH.
b) Calculate and plot the titration curve for the titration of 20.00 ml of a 0.0500 M monoprotic acid having a Ka of 1 x 10-4 with a 0.100 M NaOH solution first by assuming that all γ = 1. What is the pH and [H+] at the ½ equivalence point? What pH and [H+] is expected based on the simplest approximations and how do the values compare? Next, for the specific volume corresponding to the ½ equivalence point adjust the γ values to arrive at a convergent solution. What is the pH and [H+] when this correction is introduced and how do these values compare with the previous values?
c) Using your spreadsheet lower the Ka value of the weak acid and observe the effect on the titration curve. For what Ka does the equivalence point become difficult to distinguish? Next, using Ka’s of 1 x 10-4 and 1 x 10-7, try adjusting the concentration of the weak acid (you may want to adjust the concentration of the titrant as well) and observe the effect on the titration curve. At what formal HA concentration does the equivalence point become difficult to distinguish for these two Ka values?

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