pH & Its Importance in Everyday Life
pH एवं दैनिक जीवन में इसका महत्व
Class 10 Science – Chapter 2: Acids, Bases and Salts
CBSE Board + Foundation + Competitive Level
1. pH Scale – pH स्केल
Complete Concept – पूर्ण अवधारणा
pH is a measure of the concentration of hydrogen ions
(or hydronium ions) in an aqueous solution.
pH किसी जलीय विलयन में उपस्थित H₃O⁺ ions की सांद्रता का माप है।
pH किसी जलीय विलयन में उपस्थित H₃O⁺ ions की सांद्रता का माप है।
pH = −log[H₃O⁺]
At 25°C:
pH < 7 → Acidic / अम्लीय
pH = 7 → Neutral / उदासीन
pH > 7 → Basic / क्षारीय
pH < 7 → Acidic / अम्लीय
pH = 7 → Neutral / उदासीन
pH > 7 → Basic / क्षारीय
pH Scale
| pH | Nature | Example |
|---|---|---|
| 0–3 | Strongly acidic | Strong acids |
| 4–6 | Weakly acidic | Weak acids |
| 7 | Neutral | Pure water |
| 8–10 | Weakly basic | Mild bases |
| 11–14 | Strongly basic | Strong bases |
Logarithmic Nature of pH
The pH scale is logarithmic.
यदि pH में 1 unit का परिवर्तन होता है, तो H₃O⁺ concentration 10 times बदलती है।
For example:
pH 3 compared with pH 4:
10⁴ ÷ 10³ = 10
Therefore pH 3 solution has 10 times greater H₃O⁺ concentration than pH 4 solution.
यदि pH में 1 unit का परिवर्तन होता है, तो H₃O⁺ concentration 10 times बदलती है।
For example:
pH 3 compared with pH 4:
10⁴ ÷ 10³ = 10
Therefore pH 3 solution has 10 times greater H₃O⁺ concentration than pH 4 solution.
Solved Numerical
Question:
A solution has [H₃O⁺] = 10⁻³ mol/L. Calculate its pH.
pH = −log[H₃O⁺]
= −log(10⁻³)
= 3
Answer: pH = 3
Therefore the solution is acidic.
= −log(10⁻³)
= 3
Answer: pH = 3
Therefore the solution is acidic.
Question:
If pH = 5, calculate [H₃O⁺].
[H₃O⁺] = 10⁻pH
= 10⁻⁵ mol/L
Answer = 10⁻⁵ mol/L
= 10⁻⁵ mol/L
Answer = 10⁻⁵ mol/L
Exam Trick:
Lower pH → Higher H₃O⁺ → More acidic
Higher pH → Lower H₃O⁺ → More basic
Higher pH → Lower H₃O⁺ → More basic
2. Importance of pH in Everyday Life
Why is pH Important?
pH is important because many biological, agricultural and chemical
processes occur properly only within a particular pH range.
हमारे शरीर, मिट्टी, भोजन, दाँत और पौधों की अनेक प्रक्रियाएँ विशिष्ट pH range पर निर्भर करती हैं।
हमारे शरीर, मिट्टी, भोजन, दाँत और पौधों की अनेक प्रक्रियाएँ विशिष्ट pH range पर निर्भर करती हैं।
Major Applications of pH
- Digestive system – पाचन तंत्र
- Tooth decay – दाँतों का क्षय
- Soil pH – मिट्टी की pH
- Self-defence in animals – जीवों की आत्मरक्षा
- Plant defence – पौधों की रक्षा
- Industrial and environmental processes
Important Biological Concept
Biological enzymes generally function effectively only within suitable
pH ranges.
इसलिए शरीर के विभिन्न अंगों में pH का संतुलन अत्यंत महत्वपूर्ण है।
इसलिए शरीर के विभिन्न अंगों में pH का संतुलन अत्यंत महत्वपूर्ण है।
Foundation Question
Why is maintaining proper pH important in living organisms?
Because biochemical reactions and enzyme activities depend on suitable
pH conditions. A large change in pH can disturb normal biological
functions.
हिंदी: जैव रासायनिक अभिक्रियाएँ एवं एंजाइमों की क्रियाशीलता उचित pH पर निर्भर करती है। pH में अधिक परिवर्तन सामान्य जैविक क्रियाओं को प्रभावित कर सकता है।
हिंदी: जैव रासायनिक अभिक्रियाएँ एवं एंजाइमों की क्रियाशीलता उचित pH पर निर्भर करती है। pH में अधिक परिवर्तन सामान्य जैविक क्रियाओं को प्रभावित कर सकता है।
Exam-Ready Answer
pH is important in everyday life because it controls or influences
many biological and chemical processes such as digestion, tooth decay,
plant growth, soil fertility and defence mechanisms of animals and
plants.
3. pH in Digestive System – पाचन तंत्र में pH
Hydrochloric Acid in Stomach
Our stomach produces hydrochloric acid (HCl).
हमारे आमाशय में Hydrochloric acid (HCl) बनता है।
It provides an acidic medium that helps digestion and supports the action of digestive enzymes such as pepsin.
हमारे आमाशय में Hydrochloric acid (HCl) बनता है।
It provides an acidic medium that helps digestion and supports the action of digestive enzymes such as pepsin.
Functions of Stomach Acid
- Provides acidic medium for digestion.
- Helps pepsin function effectively.
- Helps in killing many microorganisms entering with food.
What happens when acid increases?
Excess production of HCl may cause acidity, indigestion and discomfort.
जब आमाशय में HCl की मात्रा अधिक हो जाती है तो acidity और indigestion जैसी समस्या हो सकती है।
जब आमाशय में HCl की मात्रा अधिक हो जाती है तो acidity और indigestion जैसी समस्या हो सकती है।
Role of Antacids
Antacids are mild bases that neutralise excess stomach acid.
Antacids ऐसे mild bases होते हैं जो अतिरिक्त HCl को neutralise करते हैं।
Antacids ऐसे mild bases होते हैं जो अतिरिक्त HCl को neutralise करते हैं।
HCl + NaHCO₃ → NaCl + H₂O + CO₂
Sodium hydrogen carbonate is an example of a substance that can
neutralise acid.
Other antacids may contain compounds such as magnesium hydroxide.
Question:
Why are antacids used to treat acidity?
Excess HCl in the stomach causes acidity. Antacids contain mild bases
which neutralise the excess acid and provide relief.
Answer: Antacids neutralise excess HCl in the stomach.
Answer: Antacids neutralise excess HCl in the stomach.
Remember:
Stomach → HCl → Acidic medium → Digestion
Excess HCl → Acidity
Antacid → Neutralisation → Relief
Excess HCl → Acidity
Antacid → Neutralisation → Relief
4. pH and Tooth Decay – pH एवं दाँतों का क्षय
Tooth Decay and pH
Tooth enamel is mainly made of calcium-containing mineral
(hydroxyapatite).
When the pH in the mouth falls below about 5.5, the mineral in tooth enamel begins to dissolve more readily, increasing the risk of tooth decay.
When the pH in the mouth falls below about 5.5, the mineral in tooth enamel begins to dissolve more readily, increasing the risk of tooth decay.
How Does Tooth Decay Occur?
- Food particles remain in the mouth.
- Bacteria act on sugars present in food.
- Acids are produced.
- The pH of the mouth decreases.
- At sufficiently low pH, enamel starts losing mineral.
- Repeated acid attack may lead to tooth decay.
Role of Toothpaste
Toothpaste is generally mildly basic.
It helps neutralise acids produced by bacteria and assists in maintaining oral hygiene.
It helps neutralise acids produced by bacteria and assists in maintaining oral hygiene.
Question:
Why should we brush our teeth after eating?
Brushing helps remove food particles and plaque, reducing the amount
of substrate available for bacteria to produce acids. This helps
reduce acid attack on tooth enamel.
Question:
At what pH does tooth enamel start getting damaged more readily?
When the pH of the mouth falls below approximately 5.5,
demineralisation of tooth enamel becomes more significant.
Memory Trick:
Food Sugar → Bacteria → Acid → pH ↓ → Enamel damage → Tooth decay
5. pH of Soil – मिट्टी की pH
Why is Soil pH Important?
Plants require suitable soil pH for healthy growth.
मिट्टी की pH पौधों की वृद्धि और पोषक तत्वों की उपलब्धता को प्रभावित करती है।
मिट्टी की pH पौधों की वृद्धि और पोषक तत्वों की उपलब्धता को प्रभावित करती है।
Effect of Soil pH
Different plants grow best in different pH ranges.
Very acidic or very alkaline soil can reduce the availability of certain nutrients and adversely affect plant growth.
Very acidic or very alkaline soil can reduce the availability of certain nutrients and adversely affect plant growth.
Acidic Soil
If soil is too acidic, farmers may add substances such as:
- Quick lime – CaO
- Slaked lime – Ca(OH)₂
- Limestone – CaCO₃
Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O
Alkaline Soil
If soil is too alkaline, suitable organic matter and agricultural
practices may be used to improve soil conditions.
Question:
Why is lime added to acidic soil?
Lime is basic in nature. It reacts with excess acidity and helps
neutralise acidic soil.
Answer: Lime is added to acidic soil to reduce its acidity and make the soil more suitable for plant growth.
Answer: Lime is added to acidic soil to reduce its acidity and make the soil more suitable for plant growth.
Question:
Name two substances used to reduce soil acidity.
Answer:
1. Quick lime – CaO
2. Slaked lime – Ca(OH)₂
2. Slaked lime – Ca(OH)₂
Exam Point:
Soil pH affects nutrient availability, microbial activity and plant
growth.
6. pH & Self-Defence by Animals and Plants
Self-Defence by Animals
Some animals use acidic or irritating substances as a defence
mechanism.
For example, the sting of certain insects such as ants contains acidic substances including formic acid.
For example, the sting of certain insects such as ants contains acidic substances including formic acid.
Ant Sting
An ant sting can introduce an acidic substance into the skin, causing
burning or irritation.
A mild basic substance such as baking soda solution can help neutralise the acid.
A mild basic substance such as baking soda solution can help neutralise the acid.
HCOOH + NaHCO₃ → HCOONa + H₂O + CO₂
Here:
HCOOH = Formic acid
NaHCO₃ = Sodium hydrogen carbonate
HCOONa = Sodium formate
HCOOH = Formic acid
NaHCO₃ = Sodium hydrogen carbonate
HCOONa = Sodium formate
Self-Defence by Plants
Some plants have chemical defence mechanisms.
For example, nettle leaves contain irritating substances that can cause a burning sensation on contact.
For example, nettle leaves contain irritating substances that can cause a burning sensation on contact.
Neutralisation Principle
Acidic irritation can sometimes be reduced by applying a suitable
mild base, because acid-base neutralisation reduces the acidity.
Acid + Base → Salt + Water
Acid + Base → Salt + Water
Question:
Why does an ant sting cause irritation?
An ant sting can introduce acidic substances such as formic acid into
the skin. The acid irritates nerve endings and causes a burning
sensation.
Question:
How can the effect of an ant sting be reduced?
A mild basic substance such as baking soda solution can neutralise
the acidic substance and may reduce irritation.
Memory Trick:
Ant → Formic Acid → Irritation
Baking Soda → Mild Base → Neutralisation
Baking Soda → Mild Base → Neutralisation
