Calculating pH and pOH for 0.048 M Benzoic Acid Solution

In summary, the question asks for the values of H, OH, pH, and pOH for a 0.048 mol/L solution of benzoic acid (C6H5COOH). Since it is a weak acid, its dissociation constant must be used to calculate the pH. It is recommended to try and solve the problem without looking it up in a book first, using knowledge of equilibrium equations and mass conservation. This will lead to a better understanding and more confidence in future problem solving.
  • #1
Coco12
272
0

Homework Statement



what is the H, Oh , ph and poh for a 0.048 mol/l solution of benzoic acid? C6H5COOH

Homework Equations


Ph +poh=14
Ph=-log(h30+)
H30=10^-ph

The Attempt at a Solution



I thought maybe u need to separate benzoic acid into its ions and then use the molar ratio to find the concentration of H? but what does that break down into?
 
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  • #2
C6H5COOH <-> C6H5COO- + H+

Note: it is a weak acid, so you need to use its dissociation constant to calculate pH.
 
  • #3
Ok we did not learn that yet but I will look it up in my chemistry book. Thanks
 
  • #4
Coco12 said:
Ok we did not learn that yet but I will look it up in my chemistry book. Thanks

Better still, if you haven't done it already, try and work it out without looking it up in your chemistry book. You know something about equilibrium equations and mass conservation. If you succeed you will gain confidence and understanding, if you don't succeed the explanation will mean more and be better learned when you do look it up and see maybe what key point you'd missed. If you've looked it up already, apply this principle in future problems in chemistry or any other science as far as possible. It will even make things easier for you in the long run.

:smile:
 
  • #5


To calculate the pH and pOH for a 0.048 M solution of benzoic acid (C6H5COOH), we first need to understand the dissociation of this acid in water. Benzoic acid is a weak acid, meaning it does not fully dissociate in water. It will partially dissociate into its ions: C6H5COOH ⇌ C6H5COO- + H+.

Using the equilibrium constant (Ka) for benzoic acid, we can calculate the concentration of H+ ions in the solution. Ka for benzoic acid is 6.5x10^-5, so we can set up an equilibrium expression:

Ka = [C6H5COO-][H+] / [C6H5COOH]

Since we know the concentration of benzoic acid (0.048 M), we can plug that in and solve for [H+]:

6.5x10^-5 = (x)(x) / (0.048-x)

Where x is the concentration of H+ ions. Solving for x, we get 0.0063 M. This is the concentration of H+ ions in the solution.

To find the pH, we use the equation pH = -log[H+]. Plugging in our concentration of H+, we get a pH of 2.2.

Since we know that pH + pOH = 14, we can also calculate the pOH by subtracting the pH from 14. So pOH = 14 - 2.2 = 11.8.

To find the concentration of OH- ions, we use the equation pOH = -log[OH-]. Plugging in our pOH value, we get a concentration of OH- ions of 0.000063 M.

In summary, for a 0.048 M solution of benzoic acid, the pH is 2.2, the pOH is 11.8, the concentration of H+ ions is 0.0063 M, and the concentration of OH- ions is 0.000063 M.
 

What is an acid and what are its properties?

An acid is a chemical substance that has a pH value of less than 7. It is characterized by its sour taste, ability to turn litmus paper red, and its corrosive properties. Acids are known to donate hydrogen ions (H+) in a solution.

What is a base and what are its properties?

A base is a chemical substance that has a pH value of more than 7. It is characterized by its bitter taste, ability to turn litmus paper blue, and its slippery or soapy feel. Bases are known to accept hydrogen ions (H+) in a solution.

What is the difference between a strong acid and a weak acid?

A strong acid is a substance that completely dissociates in water, meaning it releases all of its hydrogen ions. On the other hand, a weak acid only partially dissociates in water, meaning it releases some of its hydrogen ions but retains some of its original molecular form.

How is the strength of an acid or base measured?

The strength of an acid or base is measured by its pH value, which is a scale from 0 to 14 with 7 being neutral. Acids have a pH below 7, with lower values indicating stronger acids. Bases have a pH above 7, with higher values indicating stronger bases.

What are some common uses of acids and bases?

Acids and bases have a wide range of uses in various industries. Acids are commonly used in household cleaning products, food preservation, and in the production of fertilizers and pharmaceuticals. Bases are used in the production of soap, paper, and in water treatment processes.

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