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 ↓


Strong vs. Weak Acids and Bases


To understand the concept of strong and weak acids and bases, it is important to first gain a basic understanding of what acids and bases are. In simple terms, acids and bases are two types of substances that have different properties. Acids taste sour, can conduct electricity, and react with metals to form hydrogen gas. On the other hand, bases taste bitter and feel slippery.

Acids and their strengths

An acid is a substance that releases hydrogen ions ( H + ) when dissolved in water. The strength of an acid depends on how completely it ionizes, or dissociates, in water.

Strong acids

Strong acids are those that completely dissociate into their ions in water. This means that when a strong acid dissolves in water, it leaves almost all of its hydrogen ions in solution.

Examples of strong acids include:

  • Hydrochloric acid ( HCl )
  • Sulfuric acid ( H 2 SO 4 )
  • Nitric acid ( HNO 3 )
    HCl → H + + Cl -

In this reaction, hydrochloric acid completely dissociates into hydrogen ions and chloride ions.

Weak acids

Unlike strong acids, weak acids do not completely dissociate in water. Only a fraction of the acid molecules ionize, while the rest remain unchanged in solution.

Examples of weak acids include:

  • Acetic acid ( CH 3 COOH )
  • Carbonic acid ( H 2 CO 3 )
  • Phosphoric acid ( H 3 PO 4 )
    CH 3 COOH ⇌ H + + CH 3 COO -

Here, the double arrows ( ⇌ ) indicate that the reaction can occur in both directions, which means that acetic acid is partially ionized.

Bases and their strength

Bases are substances that release hydroxide ions ( OH - ) in water. Like acids, bases can be strong or weak depending on their ability to dissolve in water.

Strong bases

Strong bases dissociate completely in water, releasing a large number of hydroxide ions.

Examples include:

  • Sodium hydroxide ( NaOH )
  • Potassium hydroxide ( KOH )
  • Calcium hydroxide ( Ca(OH) 2 )
    NaOH → Na + + OH -

In this example, sodium hydroxide dissociates completely into sodium ions and hydroxide ions.

Weak bases

Weak bases do not dissociate completely in water. Instead, they release fewer hydroxide ions.

Examples of weak bases include:

  • Ammonia ( NH 3 )
    NH 3 + H 2 O ⇌ NH 4 + + OH -

Here, ammonia reacts with water to form ammonium ions and hydroxide ions, but not completely.

Visual representation of strong and weak acids

HCl H + CL -

This diagram shows the dissociation of hydrochloric acid, a strong acid. Note how it completely dissociates into hydrogen ions and chloride ions.

CH 3 COOH H + CH 3 COO -

For acetic acid, which is a weak acid, we observe only partial dissociation. Not all of the acetic acid molecules dissociate in solution.

Visual representation of strong and weak bases

NaOH Na + OH -

Sodium hydroxide, which is a strong base, dissociates completely into sodium ions and hydroxide ions.

NH 3 NH 4 + OH -

Here, ammonia partially reacts to form ammonium ions and hydroxide ions, which shows its nature as a weak base.

Role of pH in determining strength

The strength of acids and bases can also be measured using the pH scale, which ranges from 0 to 14. A low pH value indicates a strong acid, while a high pH value indicates a strong base. Neutral substances, including pure water, have a pH of 7.

  • Strong acids generally have a pH value close to 0.
  • The pH value of strong bases is generally around 14.
  • The pH value of weak acids is between 4 to 6.
  • The pH value of weak bases is between 8 to 10.

Summary

The difference between strong and weak acids and bases is determined by their ability to dissolve in water. Strong acids and bases dissociate completely, leaving more ions in solution, while weak acids and bases only partially dissociate. Recognizing examples and understanding pH values can help identify whether a substance is a strong or weak acid/base.


Grade 8 → 9.2


U
username
0%
completed in Grade 8

← Prev (9.1)
Definition and Properties of Acids and Bases
Next (9.3) →
pH Scale and pH Calculation

Comments 



Strong vs. Weak Acids and Bases

https://www.chemistryelite.com/g8/9.2?ceal=en