Homework Help: Chemistry

Posted by Meenaakshi on Friday, March 23, 2012 at 12:28am.

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 - DrBob222, Friday, March 23, 2012 at 12:31am
I agree. Thanks for showing your work. That helps a lot.

Answer this Question

Related Questions

Chemistry - Enough water is added to 0.35 g of benzoic acid to make 1000 mL of ...
Chemistry - Calculate the pH of a buffer solution that contains 0.23 M benzoic ...
Chemistry - Benzoic acid (C6H5COOH)is a monoprotic weak acid with Ka=6.30*10^-5...
chemistry - A 0.25 mol/L solution of benzoic acid, KC7H5O2 and antiseptic also ...
Chemistry - Calculate pH of a solution by mixing 15.0 mL of .50 M NaOH and 30.0 ...
chemistry - Benzoic Acid (HC6H5OO, 122.0 g/mol) has a Ka = 6.3 x 10-5. What is ...
General Chemistry 1412 inorganic - Find the pH of a solution that is 0.30 M ...
Chemistry - Given that the Ka of benzoic acid is 6.50 x 10-5, how would one ...
Chemistry - Given that the Ka of benzoic acid is 6.50 x 10-5, how would one ...
biochemistry - The pH of 0.02M solution of a weak acid was measured at 7.6. What...

For Further Reading

First Name:
School Subject:
Answer: