Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Acids, Bases and Salts ↓


pH Scale and Indicators


Introduction to the pH scale

The pH scale is an important concept in chemistry that helps us measure whether a substance is an acid, a base, or neutral. The scale ranges from 0 to 14, where:

  • A pH value less than 7 indicates an acidic substance.
  • pH 7 is considered neutral.
  • A pH value greater than 7 indicates an alkaline substance.
0 3 6 7 10 14

Acids and their properties

Acids are substances with a pH value less than 7. They have some distinctive characteristics:

  • They have a sour taste. For example, vinegar and lemon juice.
  • They can turn blue litmus paper red.
  • They react with bases to form salt and water.

Bases and their characteristics

Bases have a pH value greater than 7. Some of their characteristics are as follows:

  • They taste bitter and are slippery like soap.
  • They can turn red litmus paper blue.
  • They react with acids to form salt and water.

Neutral substances

Neutral substances have a pH value of exactly 7. Water is a common neutral substance, represented chemically as follows:

H 2 O

pH Indicator

pH indicators are substances that change colour depending on the pH of the solution they contain, helping us to identify whether the solution is acidic, alkaline, or neutral.

Normal indicators

Some of the most common pH indicators are:

  • litmus paper:
    • Blue litmus paper turns red in acidic solution.
    • Red litmus paper turns blue in alkaline solution.
  • Phenolphthalein: It turns pink in alkaline solution and remains colourless in acidic solution.
  • Methyl orange: This indicator turns red in acidic solution and yellow in alkaline solution.
Acidic Basic

Calculating pH

The pH value of a solution is calculated using the following formula:

pH = -log 10 [H + ]

where [H + ] is the concentration of hydrogen ions in the solution. For example:

If [H + ] = 0.01 M, pH = -log 10 (0.01) = 2

Importance of pH in daily life

Understanding pH is important in a variety of aspects of everyday life, including:

  • Human body: Maintaining a stable pH level in the body is essential for good health. Human blood has a slightly basic pH level, around 7.4.
  • Soil for plants: Soil pH affects plant growth. Most plants grow best in soil with a pH between 6 and 7.5.
  • Swimming pools: The pH balance of pool water is often required to be between 7.2 and 7.8 to prevent skin irritation.

Acid-base reactions

When acids and bases react with each other, they usually form salts and water. This reaction is known as neutralization. The general equation for a neutralization reaction is:

Acid + Base → Salt + Water
For example, consider the reaction between hydrochloric acid and sodium hydroxide: HCl + NaOH → NaCl + H 2 O

Buffer solution

Buffers are special solutions that resist changes in pH when small amounts of acid or base are added. They help maintain a stable pH environment.

Practical activity: pH testing

A simple experiment involves testing the pH of various household substances using litmus paper. Follow these steps:

  1. Gather various liquids, e.g., lemon juice, baking soda solution, vinegar, soapy water.
  2. Use a dropper to put a few drops of each liquid on the blue and red litmus paper.
  3. Observe the color change on the litmus paper and record the pH value based on the color chart.

Conclusion

pH scales and indicators are tools that help us understand the nature of substances. By learning to use them, we can explore the chemistry of the world around us and its applications in a variety of fields.


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Properties of bases
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pH Scale and Indicators

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