# chemistry

posted by .

Consider a 20.0mL sample of 0.105M HC2H3O2 is titrated with 0.125M NaOH.
Ka=1.8x10^-5. Determine each of the following:

a) the initial pH

b) the pH at 5.0mL of added base

c) the pH at one-half of the equivalence point

d) the pH at the equivalence point

• chemistry -

The secret to these titration problems is to know where you are on the titration curve.
a. at the beginning of the titration; therefore, you have a solution of acetic acid. Set up and ICE chart, substitute and solve for H^+ then convert to pH.

b. use the Henderson-Hasselbalch equation.
c. same as b but I can tell you the answer is pH = pKa.

d. The equivalence point pH is determined by the hydrolysis of the salt.
Set up the hydrolysis equation, write the K expression, set it equal to Kb for acetate (which is Kb = Kw/Ka) and solve for OH^-, convert to pOH, then to pH.
Post your work if you get stuck.

• chemistry -

I understand everything except for part d.
Could you show me what you mean by writing the k expression.

• chemistry -

Let's call acetate, Ac^- just to save some typing.
Ac^- + HOH ==> HAc (acetic acid) + OH^-

Kb for acetate = (Kw/Ka) where Ka is the acid constant for acetic acid.
Kb = (Kw/Ka) = (HAc)(OH^-)/(Ac^-)
Let HAc = x = OH, then
(Kw/Ka) = x^2/Ac^-.
Kw you know. Ka you know. Ac^- is the concn of acetate ion at the equivalence point which is M x L of the acid or base and that divided by the total volume. Solve for x, convert to pOH and pH.

• chemistry -

Here is the K expression (for Kb).
Kb = (Kw/Ka) = (HAc)(OH^-)/(Ac^-)

• chemistry -

is Ac^- equal to to 20 ml x the concentration? if so then I am getting the wrong answer according to my answer sheet. By the way what would my total volume be?

• chemistry -

nvm i got it. Thanks for the help

• chemistry -

for part d, how do you know the total volume at the equiv point?

## Similar Questions

1. ### chemistry

calculate the pH of the solution when 25.0ml of 0.0920M HCL is titrated with 0.15ml, 23.0ml, 30.0ml of 0.10M NaOH
2. ### chemistry

Consider the titration of 21.0 mL sample of 0.110 M HC2H3O2 with 0.130 M NaOH. what is the initial pH?
3. ### Chemistry

A 25.0mL sample of a 0.100M solution of acetic acid is titrated with a 0.125M solution of NaOH. Calculate the pH of the titration mixture after 10.0, 20.0, and 30.0 mL of base have been added.
4. ### chemistry

a 25.0ml dsmplr og 0.105M HCI was titrated with 31.5ml of NaOH. What is the concentration of the NaOH I got 0.0834M am I correct HCI + NaOH -----> H20 + NaCl 25.0ml HCI x 1L/1000mlx0.105 mol HCI/1L HCI X 1 mol NaOH/ I mol HCI = …
5. ### chemistry

2.) If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. …
6. ### chemistry

If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. …
7. ### chemistry

2.) If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. …
8. ### chemistry

2.) If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. …
9. ### chemistry

If you pass 10.0mL of a 50.0mL solution of [Co(en)2Cl2]Cl that has been reduced with Zn through a cation exchange column, you will obtain a solution that has three H+ ions for every Co3+ ion that was originally present in the sample. …
10. ### chemistry

1. 25.0mL of 0.20M Propanic acid (HC3H5O2, Ka = 1.3Ã—10-5) is titrated using 0.10M NaOH. Calculate the following pH. Show your work. a. When 0.0 mL NaOH is added. b. When 25.0 mL NaOH is added c. When 50.0 mL NaOH is added d. When …

More Similar Questions