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Understanding Hydrogen Ion Concentration, pH Scale, and Buffer Solution

Understanding Hydrogen Ion Concentration, pH Scale, and Buffer Solution

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.

What is Hydrogen Ion Concentration?

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

formula

What is the pH Scale?

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 -

  • Acidic  → < 7
  • Neutral  → = 7
  • Basic  → > 7
imi

                                                                              pH scale

Breakdown of pH Concept

If we talk about the electrical analogy, we deal with the concentration of ions:

formula

Buffer Solutions

A solution, when a small amount of acid or base is added, is a buffer if it resists the changes in pH.

  • Types of buffer:
  •       Acidic buffer →formed when a weak acid is mixed with its salt with a strong base(e.g., CH₃COOH + CH₃COONa).
  •       Basic buffer →formed when a weak base is mixed with its salt with a strong acid  (e.g., NH₄OH + NH₄Cl).
  • How it actually works:
  •       Acidic buffer: The -ve ion (in the eg: CH₃COO⁻) neutralises the extra H⁺ added.
  •       Basic buffer: The +ve ion (in the eg: (NH₄⁺) neutralises the extra OH⁻ added.

Henderson–Hasselbalch equation:

  • For acidic buffer: pH = pKa + log([salt]/[acid])
  • For basic buffer: pOH = pKb + log([salt]/[base])

Details At A Glance

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.

Ion Balance in pH

We will check the ion balance.

In neutral water: [H⁺] = [OH⁻] = 1 × 10⁻⁷ M.

  • This ensures neutrality.

In general, [H⁺] × [OH⁻] = Kw = 1 × 10⁻¹⁴ at 25°C.

Summing Up

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.

Frequently Asked Questions

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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