1. Reactivity with Water

• Definition: How a substance reacts when it comes into contact with water.
• Examples:
  • Acids: Acids react with water to form hydronium ions (H₃O⁺). For example, hydrochloric acid (HCl) dissolves in water to form hydrochloric acid solution:
    $$\text{HCl (g) + H₂O (l) → H₃O⁺ (aq) + Cl⁻ (aq)}$$
  • Bases: Bases react with water to form hydroxide ions (OH⁻). For example, sodium hydroxide (NaOH) dissolves in water to form sodium hydroxide solution:
    $$\text{NaOH (s) + H₂O (l) → Na⁺ (aq) + OH⁻ (aq)}$$
  • Metal Oxides: Some metal oxides react with water to form bases. For example, calcium oxide (CaO) reacts with water to form calcium hydroxide:
    $$\text{CaO (s) + H₂O (l) → Ca(OH)₂ (aq)}$$

2. Oxidation State

• Definition: The oxidation state of an element indicates its degree of oxidation (loss of electrons) or reduction (gain of electrons) in a chemical compound.
• Examples:
  • Iron: Iron can have different oxidation states. In iron(II) oxide (FeO), iron has an oxidation state of +2, while in iron(III) oxide (Fe₂O₃), iron has an oxidation state of +3.
  • Sulfur: In sulfur dioxide (SO₂), sulfur has an oxidation state of +4, while in sulfur trioxide (SO₃), sulfur has an oxidation state of +6.

3. Flammability

• Definition: The ability of a substance to burn or ignite, causing fire or combustion.
• Examples:
  • Hydrocarbons: Substances like methane (CH₄), propane (C₃H₈), and gasoline are highly flammable. For example, the combustion of methane in the presence of oxygen produces carbon dioxide and water:
    $$\text{CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g)}$$
  • Alcohols: Ethanol (C₂H₅OH) is flammable and is commonly used as a fuel in some engines and as a solvent.

4. Acid-Base Character

• Definition: The tendency of a substance to donate or accept protons (H⁺ ions).
• Examples:
  • Acids: Substances that donate protons. For example, sulfuric acid (H₂SO₄) is a strong acid and donates two protons in solution:
    $$\text{H₂SO₄ (aq) → 2H⁺ (aq) + SO₄²⁻ (aq)}$$
  • Bases: Substances that accept protons. For example, ammonia (NH₃) acts as a base in water by accepting a proton to form ammonium ions:
    $$\text{NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)}$$

5. Redox Potential

• Definition: The tendency of a chemical species to acquire electrons and thereby undergo reduction.
• Examples:
  • Metals: Metals like zinc (Zn) and magnesium (Mg) have a strong tendency to lose electrons and are good reducing agents. For example, in a galvanic cell, zinc loses electrons:
    $$\text{Zn (s) → Zn²⁺ (aq) + 2e⁻}$$
  • Non-metals: Elements like fluorine (F₂) and chlorine (Cl₂) have a strong tendency to gain electrons and are good oxidizing agents. For example, chlorine can oxidize iodide ions (I⁻) to iodine (I₂):
    $$\text{Cl₂ (g) + 2I⁻ (aq) → 2Cl⁻ (aq) + I₂ (s)}$$

6. Toxicity

• Definition: The degree to which a substance can harm living organisms.
• Examples:
  • Heavy Metals: Metals like lead (Pb), mercury (Hg), and cadmium (Cd) are toxic. Lead, for example, can cause severe neurological damage and is harmful to human health.
  • Pesticides: Many pesticides are toxic to insects and other organisms. For example, DDT (dichlorodiphenyltrichloroethane) was widely used but later banned due to its harmful effects on wildlife and human health.

7. Corrosiveness

• Definition: The ability of a substance to chemically attack and degrade other materials.
• Examples:
  • Acids: Strong acids like hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) can corrode metals. For example, sulfuric acid reacts with iron to form iron sulfate and hydrogen gas:
    $$\text{Fe (s) + H₂SO₄ (aq) → FeSO₄ (aq) + H₂ (g)}$$
  • Bases: Strong bases like sodium hydroxide (NaOH) and potassium hydroxide (KOH) can also be corrosive, especially to organic materials and certain metals.

8. Solubility

• Definition: The ability of a substance to dissolve in a solvent to form a solution.
• Examples:
  • Salts: Many salts are soluble in water. For example, sodium chloride (NaCl) dissolves in water to form a clear solution:
    $$\text{NaCl (s) → Na⁺ (aq) + Cl⁻ (aq)}$$
  • Organic Compounds: Some organic compounds like ethanol (C₂H₅OH) are soluble in water due to their ability to form hydrogen bonds with water molecules.