Chemistry

posted by .

Given acidity constant,Ka of benzoic acid is 6.28 X 10^-5. pH of 0.15 molar solution of this acid is ?

Here is my method:
Benzoic acid is a weak acid,hence it dissociates very little. So:
C6H5COOH---> C6H5COO- + H+
[H+] and [C6H5COO-] are yet to be calculated,so let them be x
[C6H5COOH] = 0.15-x

Since Ka= 6.28 X 10^-5 mol/L,using the Kc equation:
Ka = x.x/(0.15-x)
Assuming x<< 0.15,simplifying the eqn becomes : Ka = x.x/(0.15)

Solving the equation,x value is 3.069201851 X 10^-3 mol/L = [H+].

pH = -log[H+] = 2.51. Is this correct?
Thank you

  • Chemistry -

    I agree. Thanks for showing your work. That helps a lot.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. chemistry

    A 0.25 mol/L solution of benzoic acid, KC7H5O2 and antiseptic also used as a food preservative, has a pH of 2.40. Calculate the Ka of benzoic acid at SATP How does the benzoic acid ionization go?
  2. chemistry

    A 0.25 mol/L solution of benzoic acid, KC7H5O2 and antiseptic also used as a food preservative, has a pH of 2.40. Calculate the Ka of benzoic acid at SATP My work: C6H5COOH --> C6H5COO^- + H^+ Ka = (C6H5COO-)(H+)/ C6H5COOH I know …
  3. Chemistry

    Enough water is added to 0.35 g of benzoic acid to make 1000 mL of solution. What is the pH?
  4. 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 …
  5. 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 …
  6. 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?
  7. 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 …
  8. chemistry

    Given 20g of benzoic acid contaminated with 0.4g of salicytic acid. 1)Determine the volume of hot water required to dissolve the mass of acid. 2)Calculate the mass of benzoic acid which participates when the solution is cooled to 20°C. …
  9. organic chemistry

    How to find the volume of hot water required to dissolve the mass of acid, if we have 20g of benzoic acid contaminated with 0.4g of salicylic acid?
  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