
In order to determine the acidity or basicity of a solution, knowing the Hydrogen ion concentration [H+] is quite basic in chemistry. Thus, to show this concentration on a logarithmic scale, the pH scale is used. And when there is a condition to maintain a constant pH (acid or base added even in small quantities), a buffer solution plays an important role.
Let us understand the relationship between concentration, pH, and buffer solutions. Read on to learn their definitions and importance.
Hydrogen ion concentration is the number of moles of H⁺ ions present per litre of solution (mol L⁻¹). They are expressed in moles per litre (M).
Concentration of ions increases → acidity increases

It is a logarithm-based scale, which is used to measure the concentration of hydrogen ions.
pH= −log10[H+]
Here is the pH based on the type of solution -
pH scale
If we talk about the electrical analogy, we deal with the concentration of ions:

A solution, when a small amount of acid or base is added, is a buffer if it resists the changes in pH.
Henderson–Hasselbalch equation:
|
Property |
Details |
|
Definition of pH |
Negative logarithm of hydrogen ion concentration |
|
Neutral pH at 25°C |
7 |
|
Acidic Range |
pH < 7 |
|
Basic Range |
pH > 7 |
|
Buffer Example (Acidic) |
CH₃COOH + CH₃COONa |
|
Buffer Example (Basic) |
NH₄OH + NH₄Cl |
|
Formula |
pH = -log[H⁺] |
|
Importance |
It maintains the stability in biological and chemical systems The blood buffer (H₂CO₃ / HCO₃⁻ system) maintains pH ≈ 7.4. |
We will check the ion balance.
In neutral water: [H⁺] = [OH⁻] = 1 × 10⁻⁷ M.
In general, [H⁺] × [OH⁻] = Kw = 1 × 10⁻¹⁴ at 25°C.
Hydrogen ion concentration tells us whether a solution is acidic or basic. The pH scale expresses this concentration in a simple logarithmic form. Buffer solutions resist sudden changes in pH. Together, these ideas help us understand chemical reactions, biological systems, and many industrial processes.
Q1. Why is pH written as -log[H⁺]?
As the hydrogen ion concentrations are very small, it is easier to express them in logarithmic form.
Q2. What is the pH of pure water?
At 25°C, [H⁺] = 1 × 10⁻⁷ M, so pH = 7
Q3. Can a buffer have a pH other than 7?
Yes. Buffers can be both acidic or basic, depending on the acid-base pair used.
Q4. What happens if a strong acid is added to a buffer?
Buffer will prevent the drastic fall in pH by neutralising the acid.
Q5. What is the importance of buffers in our lives?
Buffers are responsible for maintaining a constant pH in blood and cells, which is quite essential for enzyme activity and survival.
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