Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Acids, Bases and Salts ↓


pH Scale and pH Calculation


Introduction

Understanding the pH scale and pH calculations is a fundamental part of chemistry, especially when learning about acids, bases, and salts. This concept helps us determine how acidic or alkaline a solution is. The pH scale is a numerical scale from 0 to 14 and is used to specify the acidity or alkalinity of an aqueous solution. Let's dive deeper into the details.

What is pH?

The term pH means "potential of hydrogen" or "power of hydrogen". It is a measure of the hydrogen ion concentration in a solution. When the concentration of hydrogen ions (H+) in a solution changes, it affects the pH of the solution.

The formula for calculating pH is:

pH = -log10[H+]

Here, [H+] is the concentration of hydrogen ions in moles per liter.

Acids, bases and neutral solutions

Solutions are classified based on their pH as follows:

  • Acidic: Solutions that have a pH value less than 7. An example of this is lemon juice which has a pH value of about 2.
  • Neutral: Solutions that have a pH value exactly equal to 7. Pure water is a classic example.
  • Alkaline (or alkaline): Solutions that have a pH value greater than 7. Soap can have a pH value of around 9 to 10.

pH scale

The pH scale is a logarithmic scale, meaning that each unit of change represents a tenfold change in acidity or alkalinity. That is, a solution with a pH of 3 is ten times more acidic than a solution with a pH of 4.

Here's a visual example of the pH scale:

0 1 2 3 4 5 6 7 8 9 10 11 12

How to calculate pH?

To calculate the pH of a solution, you need to know the concentration of hydrogen ions in the solution. The steps are as follows:

Step-by-step pH calculation

  1. Measure or find the concentration of hydrogen ions [H+] in moles per liter (molarity).
  2. Use the pH formula: 
    pH = -log10[H+]
  3. Solve the above expression using a scientific calculator.

Let's look at some examples:

Example 1: Calculating the pH value of lemon juice

If the concentration of hydrogen ions in a sample of lemon juice is 1.0 x 10-2 M, calculate the pH.

Use of the formula:

pH = -log10[1.0 x 10-2]

The pH value of lemon juice is 2.

Example 2: Calculating the pH of pure water

The concentration of hydrogen ions for pure water is 1.0 x 10-7 M. Calculate the pH.

Use of the formula:

pH = -log10[1.0 x 10-7]

The pH is 7, which indicates that pure water is neutral.

Example 3: Calculation of pH value of soap solution

If the concentration of hydrogen ions in soap solution is 1.0 x 10-9 M, find the pH value.

Use of the formula:

pH = -log10[1.0 x 10-9]

The pH is 9, which is basic, suitable for soap solutions.

Importance of pH in daily life

pH plays an important role in a variety of areas, including, but not limited to:

  • Human body: A specific pH range is required for the proper functioning of bodily enzymes.
  • Agriculture: Soil pH affects the availability of nutrients to plants and crop yield.
  • Aquatic life: Aquatic organisms require a certain pH level to survive.
  • Food industry: Maintaining the correct pH is important for food preservation and safety.
  • Medicine: The efficacy of some drugs may depend on pH.

pH of common substances

Below is a list of some common substances and their approximate pH values:

Substance pH
Lemon juice 2
Vinegar 3
Soda 4
Pure water 7
Blood 7.4
Hand soap 9-10
Ammonia solution 11

As we mentioned, understanding pH is important for performing a variety of chemical tasks, analyzing lab results, and it's also important in everyday life.


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Strong vs. Weak Acids and Bases
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pH Scale and pH Calculation

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