Chemistry

posted by .

A 10.00-mL sample of 0.1000 M KH2PO4 was titrated with 0.1000 M HCl
Ka for phosphoric acid (H3PO4): Ka1= 7.50x10-3
; Ka2=6.20x10-8
; Ka3= 4.20x10-10
Calculate the pH after addition of 10.00 mL of HCl to the KH2PO4 solution?

• Chemistry -

Use the Henderson-Hasselbalch equation.

• Chemistry -

which ka value would we use and would the concentrations of the acid and base be the same?

• Chemistry -

First, forget what I told you. You are titrating KH2PO4 with HCl.
KH2PO4 + HCl --> H3PO4 + KCl

You notice (which is what I didn't notice when I first read the problem) that 10 mL of 0.1M KH2PO4 is exactly neutralized (neutralized may be the wrong word) by 10 mL of 0.1M HCl so you have 0.05M H3PO4 at the equivalence point. Therefore, the pH will be determined as if you had a pure solution of 0.05M H3PO4 and for that you use k1.
..........H3PO4--> H^+ + H2PO4^-
I.........0.05.....0......0
C..........-x......x......x
E........0.05-x....x......x

Substitute the E line into k1 expression and solve for x = (H^+) and convert to pH. I expect you will need to solve the quadratic equation you will get (meaning that you can not assume 0.05-x = 0.05)

• Chemistry -

Why the ph will be determinated as if you have 0,05M H3PO4???

Similar Questions

1. Chemistry

A buffer is made up of .300 L each of .500 M KH2PO4 and .317 M K2HPO4. Assuming tha the volumes are additive, calculate a) the pH of the buffer b) the pH of the bugger after the addition of .0500 mol of HCl to .600 L of the buffer. …
2. chem

I posted a question earlier that I was having trouble with, but I was unable to attempt to try it again for several days after posting. The question was: A buffer is made up of .300 L each of .500 M KH2PO4 and .317 M K2HPO4. Assuming …
3. chemistry

I know the formula is Ma x Mla / 1000 x Sa / Sb = Mb x Mlb / 1000 if 175 ml of KOH of unknown concentration with a methyl red indicator present is titrated with [0.275 M] H3PO4, the yellow solution turns red after 29.6 ml of the H3PO4 …
4. AP CHEMISTRY

Phosphoric acid is triprotic acid (three ionizable hydrogens). The values of its stepwise ionization constants are Ka1= 7.5E-5, Ka2= 6.2E-8, and Ka3= 4.2E-13 1) Write the chemical equation for the first ionization reaction of phosphoric …
5. chemistry

For the titration of 50.00 mL of 0.1000 M ammonia with 0.1000 M HCl, calculate the pH (a) before the addition of any HCl solution, (b) after 20.00 mL of the acid has been added, (c) after half of the NH3 has been neutralized, and (d) …
6. njit

please life saver i am taking a quiz now can some one help me with this pleeeeeeeaaaaaaaaassssssseeee Calculate the pH of 0.175 M phosphoric acid (H3PO4, a triprotic acid). Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8, and Ka3 = 4.8 x 10-13.
7. chemistry

Problem: Need to prepare a 250 mL buffer of pH 7.00 using equimolar K2HPO4 and KH2PO4 solutions. Ka for phosphoric acid: Ka1=7.2 x 10^-3 Ka2=6.3 x 10^-8 Ka3=4.2 x 10^-13 I though the hard part of this was picking the right equation/Ka …
8. Chemistry

For the titration of 50.00mL of 0.1000 M ammonia with 0.1000 M HCl, calculate the pH (a) before the addition of any HCl solution (b) after 20.00mL of the acid has been added
9. AP CHEM

You need to use KH2PO4 and K2HPO4 to prepare a buffer with a pH of 7.45. Which of the following ratios of [base]/[acid] is required?
10. chemistry

Calculate the concentrations of all species present in a 0.100 M solution of weak polyprotic acid H3PO4. Ka1=7.5 x 10 ^-3, ka2 = 6.2 x 10 ^-8, Ka3= 3.6 x 10^-13 How the heck do I do this

More Similar Questions