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 ↓


Definition and Properties of Acids and Bases


Chemistry is a fascinating subject that allows us to understand the composition, structure, and properties of matter. Among the various topics of chemistry, acids and bases are fundamental concepts that provide insight into many chemical reactions and processes. Let's explore the definition, properties, and examples of acids and bases to better understand their role in chemistry.

What are acids?

Acids are substances that increase the concentration of hydrogen ions (H+) when dissolved in water. Acids have characteristic properties, such as a sour taste and the ability to turn blue litmus paper red.

Commonly known acids include:

  • Lemon juice
  • Vinegar
  • Stomach acid

The chemical formula of hydrochloric acid is represented by HCl. When HCl is dissolved in water, it dissociates into H+ and Cl- ions, as shown below:

        HCl → H+ + Cl-

Properties of acids

Acids display several characteristic properties, including:

  • Sour taste: Normal acids taste sour, such as citric acid in lemons.
  • Corrosivity: Acids can be corrosive, reacting with metals to produce hydrogen gas.
  • Electrical conductivity: Acids can conduct electricity due to the presence of ions in the solution.
  • Reactivity with metals: Acids usually react with metals to form salts and release hydrogen gas.

For example, when zinc reacts with hydrochloric acid:

        2HCl + Zn → ZnCl2 + H2

What are bases?

Bases are substances that increase the concentration of hydroxide ions (OH-) when dissolved in water. Bases are slippery and can turn red litmus paper blue.

Common examples of bases include:

  • Soap
  • Baking soda
  • Ammonia

Sodium hydroxide, commonly called lye or caustic soda, has the chemical formula NaOH. It dissociates in water to give Na+ and OH- ions, as shown in the equation below:

        NaOH → Na+ + OH-

Properties of bases

Bases have specific properties, including:

  • Bitter taste: Bases taste bitter, such as quinine in tonic water.
  • Slippery feel: Solutions of bases feel slippery like soap when touched.
  • Electrical conductivity: Bases in aqueous solution can conduct electricity.
  • Reactivity with acids: Bases react with acids to form water and salt, this reaction is called neutralization.

For example, the neutralization reaction between hydrochloric acid and sodium hydroxide is:

        HCl + NaOH → NaCl + H2O

Neutralization reaction

Neutralization reactions occur when acids and bases combine to form water and salt. This is a fundamental type of reaction in chemistry.

For example, take the reaction of acetic acid with sodium hydroxide:

        CH3COOH + NaOH → CH3COONa + H2O

This reaction results in the formation of sodium acetate (CH3COONa) and water (H2O).

Strong vs. weak acids and bases

An important distinction in chemistry is between strong and weak acids and bases. The strength of an acid or base depends on its ability to dissolve in water.

Strong acids and bases

Strong acids and bases dissociate completely in water. For example, hydrochloric acid (HCl) is a strong acid that dissociates completely into H+ and Cl-.

Strong bases, such as sodium hydroxide (NaOH), dissociate completely into Na+ and OH-.

Weak acids and bases

Weak acids only partially dissociate in water. Acetic acid (CH3COOH) is an example of a weak acid. In solution, it exists in a balance between molecules and ions:

        CH3COOH ⇌ CH3COO- + H+

Similarly, ammonia (NH3) is a weak base:

        NH3 + H2O ⇌ NH4+ + OH-

pH scale

The pH scale is a numerical representation that indicates the acidity or alkalinity of a solution. The scale ranges from 0 to 14.

  • pH < 7: Acidic solution
  • pH = 7: Neutral solution (pure water)
  • pH > 7: Alkaline solution

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

        pH = -log[H+]

where [H+] represents the concentration of hydrogen ions in mol/L.

Buffer solution

Buffers are solutions that resist changes in pH when small amounts of acid or base are added. They usually consist of a weak acid and its conjugate base or a weak base and its conjugate acid.

An important buffer system in the human body is the carbonic acid-bicarbonate buffer:

        H2CO3 ⇌ H+ + HCO3-

This system helps maintain blood pH within a narrow range despite changes in metabolic activity.

Conclusion

Understanding the definitions and properties of acids and bases is fundamental in the study of chemistry. These substances play a vital role in various chemical reactions and processes, having different characteristics that define their behavior in different environments.


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Definition and Properties of Acids and Bases

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