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.