How to Calculate pH of a Solution?
pH of a solution is a measure of how acidic or basic it is. It is measured in a scale of 0 to 14. pH or Potential of Hydrogen is a crucial measure in chemistry used to indicate the acidity or alkalinity of a solution. It measures the concentration of hydrogen ions (H+) in a solution. Understanding pH is essential in various fields, from chemistry and biology to environmental science and healthcare.
In this article, we are going to study about pH and cover various methods to calculate the pH of different solutions.
Table of Content
- What is PH
- How to calculate pH of solution?
- Using a pH Meter
- Using pH Indicators
- Calculation of pH from Concentration
What is pH?
pH stands for “Potential of hydrogen” and refers to the measurement of acidity or alkalinity of a solution. It is a scale ranging from 0 to 14, where 7 is neutral, Below 7 is acidic and above 7 is basic.
How to Calculate pH of Solution?
Understanding how to calculate the pH of a solution is fundamental in chemistry and is essential for various applications. So here, we will see about pH and cover various methods to calculate the pH of different solutions.
Using a pH Meter
We can calculate the pH of a solution with the help of a pH meter using the steps below:
Step 1: Calibrate the pH Meter: Before measuring the pH meter is calibrated using buffer solutions of known pH.
Step 2: Immerse the pH Electrode: Place the clean electrode into the solution.
Step 3: Read the pH: The pH meter will display the pH of the solution.
Using pH Indicators
We can calculate the pH of a solution with the help of a pH indicators using the steps below:
Step 1: Select the indicator: Choose an appropriate indicator based on the expected pH range of the solution.
Step 2: Add Indicator: Add a few drops of the indicator to the solution.
Step 3: Observe color change: The color change will indicate the approximate pH of the solution based on the indicator’s color chart.
Calculation of pH from Concentration
If you know the concentration of H+ ions you can calculate pH using:
pH = – log10[H+]
Common pH Ranges
- 0-6.9 Acidic
- 7 : Neutral
- 7.1 -14 : Basic or Alkaline
Remember, pH is a logarithmic scale, so each whole pH value below 7 is 10 times more acidic, and each whole pH value above 7 is 10 times more basic.
Self Ionization of Water
The self ionization of water is when water molecule, spontaneously dissociates into ions. This happens into a small amount, but it is crucial for many chemical reactions.
The equation for the self ionization of water is:
2 H2O (l) ↹ H3O+(aq) + OH– (aq)
In this reaction, one water molecule acts as an acid by donating a proton (H+) to another water molecule, which acts as a base. This forms a hydronium ion (H3O+) and a hydroxide ion (OH–). The concentration of these ions in pure water at room temperature are each about 1 × 10-7moles per liter.
pH: The term pH refers to the “potential of hydrogen ion”.
pH = -log[H3O+]
pOH: The pOH of an aqueous solution, which is related to the pH, can be determined by the following equation.
pOH = -log [OH–]
Relating pH and pOH
Another equation can be used that relates the concentrations of hydronium and hydroxide concentrations. This equation is derived from the equilibrium condition for the self-ionization of water, Kw. It brings the three equations for pH, pOH, and Kw together to show that they are all related to each other and either one can be found if the other two are known. the following equation is expressed by taking the negative logarithm of the Kw expression for the self-ionization of water at room temperature.
Kw = [H3O+] [OH–] = 1.0 × 10 -14
pKw = pH + pOH = 14
Importance of Studying pH
Understanding pH is very important across various fields due to its significant implications in chemistry, biology and other fields. Here are some important reasons or importance of studying pH
Biological Processes: pH plays a vital role in biological system. Enzymes for example has optimal pH at which they function best.
Chemical reactions: pH is crucial factor in many chemical reactions, it helps us to how acidic or basic the solution is, which in turns predicts how chemicals will react with each other.
Environmental Impact: pH affects the environment significantly. From the health of aquatic eco system to the impact of acid rain on soil and water, pH is a key indicator of environmental health.
Water quality: pH is a primary indicator for water quality whether it’s for drinking water or aquatic habitats, monitoring pH ensure water is safe for its intended use.
Examples of pH Calculation
Example 1: A Solution is 0.055 M HBr. What is the pH of this solution?
Solution: Use the pH equation which is
pH = -log [H3O+]
0.055 M HBr, HBr is a strong acid.
[H3O+] = 5.5 × 10-2 M
pH = -log (5.5 × 10-2) = 1.26
Example 2: Determine the pH of a 0.010 M HNO3 Solution.
Solution:
Use the pH equation which is
pH = – log [ H+ ]
pH = – log [ 1.0 × 10-2 ]
pH = -(-2.0) = 2.0
Example 3: Calculate the pH of a solution of 0.0025 M H2SO4.
Solution:
pH = -log [2(2.5 × 10-3)
pH = -(-2.3) = 2.3
Example 4: What is the hydrogen ion concentration of an aqueous HCl solution that has a pH of 3.0?
Solution:
Use the pH equation which is pH = -log [ H+]
3.0 = – log [ H+]
[H+] = 1.0 × 10-3M
Example 5: What is the pH of a 2.5 × 10-6 M solution of HCl ?
Solution:
We can write equation for of a 2.5 × 10-6 M solution of HCl as
pH = -log [2.5 × 10-6]
pH = – (-5.6) = 5.6
Also, Check
FAQs on How to Calculate pH of a Solution
Which of the following is the formula for pH calculation?
pH is defined as the negative logarithm of hydrogen ion concentration. Hence, its formula is -log10[H+].
Who invented the pH Scale?
In 1909 S.P.L. Sorenson a Danish Chemist, introduced the concept of pH as a convenient way of expressing acidity. pH scale tests the acidity or alkalinity of a substance or solution.
What is the pH value of very strong acid solution?
Solution with pH value between 0 to 1 are known to be strongly acid solution. The acidity decreases as the value of pH increases from 0 to 7.
What is the pH value of pure water?
Pure water has a pH value of 7. It is considered “neutral” because it has neither acidic nor basic qualities.
Water is a weak or strong electrolyte?
Pure water is a weak electrolyte. It dissociates to form hydrogen ions and hydroxyl ions.