What is pOH?
pOH or power of hydroxide ion is a standard used to estimate hydroxide ion (OH–) concentration in a solution. It is used to express the basicity of a solution. It is equivalent to the negative logarithm of hydroxide ion concentration.
pH = – log [OH–]
What is pH?
pH or power of hydrogen ion is a standard used to estimate hydrogen ion (H+) concentration in a solution. It is used to express the acidity of a solution. It is equivalent to the negative logarithm of hydrogen ion concentration.
pH = – log [H+]
Table of Content
- Understanding pOH and pH in detail
- pOH to pH
- pH and pOH value of a few molecules
- Difference between pOH and pH
- Frequently Asked Questions – FAQs
Understanding pOH and pH in detail
pOH or power of hydroxide ion is a standard used to estimate hydroxide ion (OH–) concentration in a solution. It is used to express the basicity of a solution.
- It is equivalent to the negative logarithm of hydroxide ion concentration.
pH = – log [OH–]
If the pOH value is less than 7, the solution is basic, or if the pOH value is more than 7, the solution is acidic, or if the pOH value is equivalent to 7, then the solution is neutral.
In contrast, pH or power of hydrogen ion is a standard used to estimate hydrogen ion (H+) concentration in a solution. It is used to express the acidity of a solution.
- It is equivalent to the negative logarithm of hydrogen ion concentration.
pH = – log [H+]
If the pH value is less than 7, the solution is acidic, or if the pH value is more than 7, the solution is basic, or if the pH value is equivalent to 7, then the solution is neutral.
Both pOH and pH are associated. With an increase in pOH value, pH decreases or with an increase in pH value, pOH decreases.
I.e. pOH ∝ 1 / pH
pOH to pH
Consider dissociation of water,
H2O ⇆ H+ + OH–
The dissociation constant, Kw, would be,
Kw = [H+][OH–]
Here, Kw is dissociation constant, [H+] is hydrogen ion concentration, and [OH–] is hydroxide ion concentration.
Take the negative logarithm of both sides.
-log Kw = – log [H+] [OH–]
-log Kw = -(log [H+] + [OH–] )
-log Kw = -log [H+] – log [OH–] . . . 1
We know that,
Kw = 1 X 10 -14 at 298 K
-log [H+] = pH
-log [OH–] = pOH
So, equation 1 is equal to
-log 1 X 10 -14 = pH + pOH
14 = pH + pOH
pOH = 14 – pH
pH = 14 – pOH
Hence if the pOH is known, we can quickly determine the pH value.
pH and pOH value of a few molecules
S No. |
Name of the Molecule |
pH at 1 mM concentration |
pOH at 1 mM concentration |
---|---|---|---|
1. |
Sulfuric acid |
2.75 |
11.25 |
2. |
Nitric Acid |
3.01 |
10.99 |
3. |
Hydroiodic Acid |
3.01 |
10.99 |
4. |
Hydrobromic Acid |
3.01 |
10.99 |
5. |
Hydrochloric Acid |
3.01 |
10.99 |
6. |
Hydrofluoric Acid |
3.27 |
10.73 |
7. |
Orthophosphoric Acid |
3.06 |
10.94 |
8. |
Sodium Hydroxide |
1 |
13 |
9. |
Potassium Hydroxide |
1.48 |
12.52 |
Difference between pOH and pH
S No. |
pH |
pOH |
---|---|---|
1. |
pH refers to the power of hydrogen ions. |
pOH refers to the power of hydroxide ions. |
2. |
It is a standard used to estimate a solution’s hydrogen ion (H+) concentration. |
It is a standard used to estimate a solution’s hydroxide ion (OH–) concentration. |
3. |
It is equivalent to the negative logarithm of hydrogen ion concentration. pH = – log [H+] |
It is equivalent to the negative logarithm of hydroxide ion concentration. pH = – log [OH–] |
4. |
If the pH value is less than 7, the solution is acidic. |
If the pOH value is less than 7, the solution is basic. |
5. |
If the pH value is more than 7, the solution is basic. |
If the poH value is more than 7, the solution is acidic. |
Frequently Asked Questions on pOH to pH
What is pH?
pH or power of hydrogen ion is a standard used to estimate hydrogen ion (H+) concentration in a solution. It is used to express the acidity of a solution.
- It is equivalent to the negative logarithm of hydrogen ion concentration.
pH = – log [H+]
If the pH value is less than 7, the solution is acidic, or if the pH value is more than 7, the solution is basic, or if the pH value is equivalent to 7, then the solution is neutral.
What is pOH?
pOH or power of hydroxide ion is a standard used to estimate hydroxide ion (OH–) concentration in a solution. It is used to express the basicity of a solution.
- It is equivalent to the negative logarithm of hydroxide ion concentration.
pH = – log [OH–]
If the pOH value is less than 7, the solution is basic, or if the pOH value is more than 7, the solution is acidic, or if the pOH value is equivalent to 7, then the solution is neutral.
Are pH and pOH related?
Yes, pH and pOH are related. With an increase in pOH value, pH decreases or with an increase in pH value, pOH decreases. The sum of pH and pOH value is equivalent to 14.
pH + pOH = 14
Calculate the pH of a solution having pOH 2?
Given,
pOH = 2,
We know that,
pH + pOH = 14
pH = 14 – pOH
pH = 14 – 2
pH = 12
How will you convert pOH to pH?
Using the pH = 14 – pOH formula, we can convert pOH to pH.
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