biochemistry

posted by .

The pH of 0.02M solution of a weak acid was measured at 7.6. What is the [OH-] in this
solution?
B) The Ka for benzoic acid is 6.4 x 10-5M. 150 ml of 0.1 M NaOH is added to 200 ml of 0.1 M
benzoic acid, and water is added to give a final volume of 1 L. What is the pH of the final solution?

• biochemistry -

A). pH = -log(H^+)
7.6 = -log(H^+). Solve for (H^+). You should get approximately 2.5E-8.

B)
150 mL x 0.1M NaOH = 15 millimiles.
200 mL x 0.1M benzoic acid = 20 mmols.

Let's call benzoic acid HB, then
............HB + NaOH ==> NaB + H2O
initial....20......0........0.....0
change.....-15...-15........15...15
equil.......5......0.........15
pH = pKa + log (base)/(acid)
pH = 4.19 + log (15/5); solve for pH.

Note and this is important:
I used millimoles (the equivalent of mol) INSTEAD of concentration. The HH equation calls for concentration. I used millimoles as a shortcut. The answer will be the same; however, some profs will count off if you use mols (or millimoles) instead of concentration. So you need to do one of three things if your prof is picky (as I am).
(base) = mmols/mL = 15/1000 = ?
(acid) = mmols/mL = 5/1000 = ?
#1.
pH = 4.19 + log(0.015/0.005) = ?
#2.
pH = 4.19 + log(15/1000/5/1000) =
= cancel the denominator since both are the same (by the way they will ALWAYS be the same) so
= 4.19 + log(15/5) = ?
or third,
pH = 4.19 + log(15/volume/(5/volume) =
cancel v and
pH = 4.19 + log (15/5) = ?

Similar Questions

1. College Chemistry

A 30.00 mL volume of a weak acid, HA, (Ka = 3.8 x 10^-6) is titrated with 39.00 mL of 0.0958 M NaOH to the equivalence point. A.) What is the pH of the acid solution, before any base is added to it?
2. Chemistry

You have 150 ml of a solution of benzoic acid in water estimated to contain about 5 g of acid. The distribution coefficient of benzoic acid in benzene and water is approx 10. Calculate the amount of acid that would be left in the water …
3. Chemistry

You have 150 ml of a solution of benzoic acid in water estimated to contain about 5 g of acid. The distribution coefficient of benzoic acid in benzene and water is approx 10. Calculate the amount of acid that would be left in the water …
4. Chemistry III

Assume you dissolve 0.240 g of the weak acid benzoic acid, C6H5CO2H, in enough water to make 1.16 102 mL of solution and then titrate the solution with 0.153 M NaOH. C6H5CO2H(aq) + OH -(aq) C6H5CO2-(aq) + H2O(l) (a) What was the pH …
5. AP Chemsitry

A solution of an unknown monoprotic weak acid was titrated with 0.100 M NaOH. The equivalence point was reached when 37.48 ML of base had been added. From a second buret, exactly 18.74 of 0.100 M HCl were added to the titration solution. …
6. Chemistry

I took 25 mL of an unknown weak acid and added it to 10 mL of NaOH solution. I measured the pH and got 2.88 with concentration of NaOH @ .0098 and weak acid at 0.0102. What is pKa for the acid?
7. Chemistry

Benzoic acid (C6H5COOH)is a monoprotic weak acid with Ka=6.30*10^-5. What is the pH of a solution of benzoic acid that is 0.559M and has 2.25*10^-2M NaOH added?
8. chemistry

enzoic acid is a weak monoprotic acid with Ka = 6.5×10-5 M. NaOH(s) was gradually added to 1.00 L of 8.66×10-2 M benzoic acid. 1. Calculate the pH of the solution before the addition of the base. 2. Calculate the pH of the solution …
9. Chemistry (Acid/Base)

Consider a solution made by mixing 100 mL of 2.0 M acetic acid (Ka= 1.8e-5) with 100 mL of 0.00020 M benzoic acid (Ka= 6.4e-5). How many moles of solid NaOH must be added to the solution so that half of the benzoic acid is protonated …
10. Chemistry

References Chapter 17: EOC Assume you dissolve 0.178 g of the weak acid benzoic acid, , in enough water to make mL of solution and then titrate the solution with 0.187 M . ( for benzoic acid = .) What was the pH of the original benzoic …

More Similar Questions