Lecture on Reactivity of Elements and Acids/Bases

  • Reactivity of Elements

    • Elements vary in their reactivity, which can be ranked on a spectrum.
    • Low Reactivity: Example - Platinum
    • Does not react with sulfuric or hydrochloric acid.
    • Extremely unreactive.
    • High Reactivity: Examples - Lithium, Sodium, Potassium
    • React with water and ignite spontaneously, producing hydrogen gas, which is also flammable.
    • Many demonstrations available on platforms like YouTube.
    • Aluminum
    • Located closer to the highly reactive metals (like sodium) on the reactivity spectrum.
    • Contrary to common perception, aluminum is reactive and can be used to create rocket fuel.
    • Forms a protective layer of aluminum oxide when exposed to air, preventing further reactions.
    • This oxide layer explains its common uses, such as cooking or in aircraft.

  • Introduction to Acids and Bases

    • Acids and bases are essential compounds in chemistry, heavily involved in various reactions and processes.
    • Acids
    • The most produced chemical compound is sulfuric acid due to its versatility and cost-effectiveness.
    • Commercial Importance: Often the first choice for engineers needing an acid unless unsuitable.
    • Common Acids in Daily Life
    • Vinegar (5% acetic acid), cream of tartar, and soda are examples of mild acids found at home.
    • Soda is notably acidic; it can dissolve a tooth immersed in it over time.
    • Citrus fruits like lemons contain citric acid.

  • Common Bases in Daily Life

    • The most familiar base is baking soda (sodium bicarbonate), which is mildly basic and safe to handle.
    • Other bases include soap, ammonia (in Windex), and bleach.
    • Drano, a strong base, is used for unclogging pipes.

  • Basic Definitions of Acids and Bases

    • Acid: Produces H⁺ ions in solution.
    • Base: Produces OH⁻ ions in solution.
    • Hydrogen Ions Representation: For simplicity, traditionally represented as H⁺, but more accurately as H₃O⁺ in solutions (hydronium ion).
    • Disassociation: Strong acids like Hydrochloric Acid (HCl) fully disassociate in water, whereas weak acids do not completely disassociate.

  • Acid and Base Strength

    • Strong Acids: Fully disassociate in solutions.
    • Examples include HCl, HNO₃, H₂SO₄.
    • Weak Acids: Partially disassociate, leaving most molecules intact in solution.
    • Example: HF remains mainly as HF in solution.
    • Visualizing Dissociation
    • Dynamic Equilibrium: In weak acids, a small fraction disassociates but is always balanced with the undissociated forms.
    • Equations involving H⁺ (acid) and OH⁻ (base) when combined produce water (H₂O), exemplifying acid-base neutralization.

  • Oxidation and Reduction Reactions (Redox)

    • Definition: Redox reactions involve the transfer of electrons, where oxidation involves loss of electrons and reduction involves gain.
    • Mnemonics:
    • OILRIG - Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).
    • Oxidation States
    • Used for bookkeeping electron transfer in compounds, defined numerically for each atom.
    • Example: In elemental magnesium and oxygen, both start with an oxidation state of 0 and form compounds with +2 and -2 states, respectively in MgO.