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 → Metals and Nonmetals ↓


Corrosion and its prevention


Corrosion is a natural process that slowly deteriorates materials, especially metals, due to chemical or electrochemical reactions with their environment. Although we often think of metals when discussing corrosion, some non-metals can also suffer from similar degradation. Understanding corrosion, its causes, and methods of prevention is important to preserve the materials used in buildings, machines, and everyday products.

What is corrosion?

Corrosion is the process in which materials, especially metals, are slowly destroyed by reacting with environmental elements such as oxygen, water, acids or salts. This reaction forms undesirable compounds and eventually weakens the material, leading to failure.

Example of iron corrosion

The most common example of corrosion is the rusting of iron or steel. Iron reacts with oxygen in the presence of water to form iron oxide, commonly known as rust. The chemical reaction is described below:

4Fe + 3O 2 + 6H 2 O → 4Fe(OH) 3

Rust appears as a flaky, brown layer on the surface of iron objects, and it continues to spread unless it's stopped.

steel War

Causes of rust

Many environmental factors contribute to corrosion, including, but not limited to, the following:

  • Moisture: Water plays an important role in the rusting process. It accelerates rusting in a humid environment.
  • Oxygen: The presence of oxygen, especially in the air and dissolved in water, facilitates the oxidation of metals.
  • Salt: Salt water found in coastal areas acts as an electrolyte which accelerates the corrosion process.
  • Acids and pollutants: Acidic conditions increase the rate of corrosion. Pollutants such as sulfur dioxide can form acids in the presence of moisture.

Types of corrosion

Corrosion can appear in different forms depending on the environmental conditions and the materials involved. Some of the common types are:

Uniform corrosion

This is the most common form in which rust spreads evenly across a surface. Over time, it weakens the entire material evenly.

Pitting corrosion

Pitting occurs when tiny holes or pits form on the surface of a metal. This localized attack can cause serious damage without much visible damage to the surface.

Galvanic corrosion

This occurs when two different metals come into contact with each other in the presence of an electrolyte. The more reactive metal (the anode) corrodes more rapidly than the less reactive metal (the cathode).

Anode (reactive metal) cathode (less reactive metal) Electrolyte

Stress corrosion

When a metal under stress is exposed to a corrosive environment, it can fail unexpectedly. The combination of tensile stress and corrosion causes cracks to form.

Corrosion in non-metals

While metals are most commonly associated with corrosion, nonmetals can also deteriorate, although not always through the same mechanisms. For example, rubber can crack from exposure to oxygen, and plastics can deteriorate from exposure to ultraviolet (UV) light.

Rust prevention

Preventing corrosion is important to maintain the integrity and longevity of structures and products. Here are some common methods:

Protection by coatings

Applying a protective coating, such as paint, can isolate the metal from environmental factors. This creates a barrier to prevent moisture and oxygen from reacting with the metal.

Galvanization

Galvanization is the coating of a layer of zinc on iron or steel. Zinc acts as a sacrificial metal, which rusts first instead of the iron. It provides both barrier protection and galvanic protection.

Zinc steel

Cathodic protection

This method involves connecting the metal to be protected to a more reactive metal. For example, magnesium or zinc rods are used to protect an iron structure. These sacrificial anodes will rust instead of the iron.

Metal alloys

Corrosion resistance can be improved by using alloys rather than pure metals. Stainless steel is an example of this, which contains chromium that forms a protective oxide layer.

Iron + Chromium (12% or more) → Stainless Steel

Design revisions

Improving the design to avoid the accumulation of water and pollutants can help reduce corrosion. Ensuring good drainage and avoiding sharp corners can reduce areas prone to corrosion.

Environmental control

Controlling the environment in which materials are stored can also extend their life. Reducing the amount of moisture, acidity or salinity in the environment helps slow corrosion.

Routine maintenance

Regular inspection and maintenance can detect corrosion early and prevent its spread. Cleaning, repainting, or replacing parts may be part of maintenance activities.

Conclusion

Corrosion is a significant issue that affects both metals and some non-metals. Its impact can be costly in terms of safety and economic factors. Understanding the causes and implementing preventive measures can substantially reduce its effects and increase the lifespan of materials and structures.


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Corrosion and its prevention

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