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pH Scale
1.0Master the pH Scale in Minutes
Discover how to accurately measure the chemical strength of acids and bases. Learn the significance of the pH scale, its color transitions, and its critical role in nature and biological systems through clear rules and exam-focused explanations.
2.0Learning Outcomes
After completing this lesson, you will be able to:
- Define pH and explain the origin of its name.
- Classify solutions as acidic, basic, or neutral based on their pH values.
- Relate changes in pH with changes in the concentration of hydrogen ($H^+$) and hydroxyl ($OH^-$) ions.
- Associate universal indicator colors with specific pH ranges.
- Explain the practical importance of pH in biological systems, agriculture, and everyday life.
3.0Introduction
Chemistry helps us understand the acidic or basic nature of substances around us. One of the most important concepts in Class 10 Science Chapter – Acids, Bases and Salts is the pH scale. The pH scale is used to measure how acidic or basic a substance is.
Different substances such as lemon juice, soap solution, vinegar, and water have different pH values. The pH scale helps scientists, doctors, farmers, and industries determine the chemical nature of solutions accurately.
Understanding the pH scale is important for board examinations as well as daily life applications. In this article, you will learn about pH full form, pH scale acids and bases, water pH scale, pH scale examples 0-14, and the importance of pH in simple and easy-to-understand language.
4.0What is pH?
The pH value of a substance tells us whether the substance is acidic, basic, or neutral. The term pH is used to measure the concentration of hydrogen ions in a solution.
The pH full form is "Potential of Hydrogen."
Sometimes it is also called:
- Power of Hydrogen
- Potential Hydrogen
The pH scale was introduced by Danish scientist Søren Peder Lauritz Sørensen in 1909. pH Scale is a numerical scale used to measure the acidic or basic strength of substances.
The pH scale generally ranges from: 0 to 14
The value depends on the concentration of hydrogen ions present in the solution.
5.0pH Scale Name and Range
The pH scale name comes from the term “Potential of Hydrogen.”
Lower pH values indicate stronger acids, while higher pH values indicate stronger bases.
6.0pH Scale: Acids and Bases
The pH scale acts as a chemical yardstick. It is divided into three distinct zones based on the concentration of hydrogen ions (H+) versus hydroxyl ions (OH-):
- pH < 7 (Acids): Solutions with a pH lower than 7 are acidic. The lower the number, the stronger the acid. (Higher concentration of H+ ions).
- pH = 7 (Neutral): A pH of exactly 7 is completely neutral. It is neither acidic nor basic.
- pH > 7 (Bases/Alkalis): Solutions with a pH higher than 7 are basic (or alkaline). The higher the number, the stronger the base. (Higher concentration of OH- ions).
Important Concept: As pH decreases from 7 to 0, acidity increases. As pH increases from 7 to 14, basicity increases.
7.0pH Scale Examples 0-14
Understanding pH scale examples helps students remember the concept easily.
pH Scale Examples from 0 to 14
These examples help understand the acidic and basic strength of substances.
8.0Water pH Scale
The pH of water depends heavily on its purity and what is dissolved in it:
- Pure Distilled Water: Has a pH of exactly 7.0. It is perfectly neutral because the concentration of H+ and OH- ions is perfectly balanced.
- Normal Drinking Water / Tap Water: Typically ranges between 6.5 and 8.5 depending on local mineral content.
- Ocean Water: Is slightly basic, hovering around a pH of 8.1 due to dissolved salts and carbonates.
9.0Universal Indicator and pH Scale Colors
Universal Indicator changes color according to pH values.
These colors help identify the strength of acids and bases.
10.0EUREKA by ALLEN – Premium Online Learning for Class 10
EUREKA by ALLEN is designed to simplify, enrich, and enhance your experience in Class 10. Through the use of fun and engaging video lessons, regular practice tests, and immediate help for any doubts you may have regarding the material; students have a firm understanding of the concepts they are studying and feel confident in their preparation for their board exams. No matter if you are attempting to receive a higher mark or develop a better understanding of your studies, EUREKA will support you as you continue to grow as a learner.
11.0Supporting Study Materials
This study material, including CBSE Notes and NCERT Solutions for the Chapter "Acids, Bases and Salts" focusing on Indicators, is designed according to the latest CBSE Class 10 Science syllabus and NCERT guidelines. It provides clear definitions, comparative tables, and essential experimental knowledge to help students master the identification of chemical substances effectively.
12.0Previous Year Questions (PYQs) on pH Scale
Q1. Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is:
(a) neutral,
(b) strongly alkaline,
(c) strongly acidic,
(d) weakly acidic,
(e) weakly alkaline? Arrange the pH in increasing order of hydrogen ion concentration. (CBSE Board)
Answer: Classification:
(a) Neutral: Solution D (pH = 7)
(b) Strongly alkaline: Solution C (pH = 11)
(c) Strongly acidic: Solution B (pH = 1)
(d) Weakly acidic: Solution A (pH = 4)
(e) Weakly alkaline: Solution E (pH = 9)
13.030-Second Review: pH Scale
- pH < 7 (Acids): Solutions with a pH lower than 7 are acidic. The lower the number, the stronger the acid. (Higher concentration of H+ ions).
- pH = 7 (Neutral): A pH of exactly 7 is completely neutral. It is neither acidic nor basic.
- pH > 7 (Bases/Alkalis): Solutions with a pH higher than 7 are basic (or alkaline). The higher the number, the stronger the base. (Higher concentration of OH- ions).
In Class 10 Science, you need to know how pH affects living organisms:
- Our Body: Functions best within a narrow pH range of 7.0 to 7.8.
- Tooth Decay: Starts when the pH in our mouth falls below 5.5. Bacteria break down food particles to produce acids that corrode tooth enamel. Toothpaste is basic to neutralize this.
- Soil pH: Plants require a specific pH range for healthy growth. If soil is too acidic, farmers treat it with quicklime {CaO} or slaked lime {Ca(OH)}2.
- Self-Defense by Animals: Honeybee stings inject an acidic liquid, causing pain. Applying a mild base like baking soda provides relief.