pOH is a technique for the measurement of the hydroxide ion concentration of a solution to identify the alkalinity of a solution. It shows a value less than 7 for the alkaline solution and more than for the acidic solution. At 25 degrees Celcius, the neutral solution shows this value is correct 7. The strength of acidity or basicity can be measured easily by calculating this value. This article describes the definition, examples, formula, scale, calculations, and uses of this issue.
Definition
It represents the negative logarithm of the hydroxide ion (OH–) concentration in an aqueous solution.
This value ranges from 0 to 14, where 7 is neutral. This value is very low for a higher alkaline solution, whereas a higher acidic solution has more value than 7.
Calculations Technique
This calculation depends on the value of pH or hydrogen ion concentration ([H+]). The concentration of hydrogen ion and hydroxide ion (OH-) are related to each other in the following way:
[OH–] = Kw / [H+]
Where Kw represents the constant self-ionization value of water molecules. It can take the logarithm of both sides and get the following equation:
pOH = pKw – pH => 14 – pH
Importance
It describes the strength of acidity or alkalinity of the selected solution.
The hydroxide ion concentration is easily found by calculating this value.
Calculations (From molarity)
This value can be calculated easily from the value of molarity. We know that it expresses the negative log of hydroxide ion (OH–) concentration and can be shown by the following formula:
pOH = – log [OH–]
This value can be calculated by following the above formula if we put the value of hydroxide ion concentration.
Example: An aqueous solution has a molarity of 6.3 × 10-5 M. Now calculate the hydroxide ion concentration in this solution.
Solution: We know the following formula to calculate this value,
pOH = – log [OH–]= – log [ 6.3 × 10-5] = 4.2
Calculation (from pH)
We can use the value of pH to determine this value. We consider the following dissociation matter of water:
H2O < — > H+ + OH–
The dissociation constant, Kw can be represented by the following,
Kw = [H+] [OH–]
The dissociation constant value of water contains 1 X 10 -14 values at 298 K.
It must take a negative logarithm of both sides of the above equation, then we get.
– log Kw = – log [ H+] [OH–]
-log Kw = – (log [ H+] + [ OH–])
-log Kw = – log [H+] – log [OH–] . . …… (i)
We know that,
-log [H+] = pH
-log [OH–] = pOH
Putting this value in equation (i)
-log (1 X 10 -14) = pH + pOH
14 = pH + pOH
pOH = 14 – pH
Calculations (From pKb)
We calculate this value from the value of pKb by helping the Henderson equation with the following:
pOH = pKb + log {[salt] / [Base]} . . . (i)
The concentration of salt and the concentration of acid is equal to each other at the equivalence point.
So, we can write the (i) no equation by the following,
pOH = pKb
Let the values of [salt] / [Acid] be equal to 10 and put this value in equation (i) and then we can write,
pOH = pKb + log 10 =pKb + 1
Let the value of [salt] / [Acid] be equal to 1 / 10 and Put this value in equation (i).
pOH = pKb + log 1 / 10 => pKb + log 1 – log 10 => pKb – 1
Uses
The proper value of this factor is very important to maintain in our working fields. The specific value of this factor is essential for the food preservation issue. The right value of this matter is very important in the fields of RO water purification, agriculture, fertilizer, medicine, chemistry, engineering, etc. The various stock solution is prepared in the chemistry laboratory by maintaining this value.
Some Math’s
Frequently Asked Questions (FAQs)
What is pOH in chemistry?
It represents the hydroxide ion concentration in a solution for measuring the acidity or alkalinity of a solution.
The solution is neutral when it contains a value is 7. The solution has an alkalinity if this value is less than 7. The solution is acidic when it shows values more than 7.
pOH = – log [OH–]
It is used to determine the strength of solutions and their various characteristics.
How can we determine the pOH value from the solution molarity?
We can use molarity to determine this value. It is generally equivalent to the negative logarithm of hydroxide ion (OH–) concentration which is represented as the following:
pOH = – log [OH–]
We can determine this value by putting the hydroxide ion concentration on the above equation.
How can we determine the pOH from the value of pKb?
This value can be calculated by applying Henderson’s acidic buffer equation. The Henderson’s acidic buffer equation is represented as the following:
pOH = pKb + log {[salt] / [Base]} . . . (i)
The salt concentration and base concentration are the same. So, the (i) no equation can be written as the following:
pOH = pKb
What is the full meaning of pOH?
Its full meaning is the potential of hydroxide ion concentration in an aqueous solution.
This value can be measured from the molarity of the solution, the values of pH, and the values of pKb.
