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Solutions, Mixtures, Acids, Bases, and pH

Solutions

  • Definition: Homogeneous mixtures where components are dissolved and permanently and equally distributed.
  • Two Parts of a Solution:
    • Solute: The chemical(s) that dissolve into the solution.
      • Example: Sugar in sugar water.
    • Solvent: The chemical that the solute(s) dissolve into.
      • Example: Water in sugar water (water is often called the "universal solvent").
    • Combined: Sugar (solute) + Water (solvent) \rightarrow Sugar Solution.
    • Example: Vinegar in water (vinegar is a solution itself, implying acetic acid is a solute in water).

Hydrophobic Substances

  • Definition: "Water-fearing" chemicals that do not dissolve in water.
  • Characteristics: Unable to form a solution when mixed with water.
  • Molecular Structure: Include molecules that only contain non-polar covalent bonds.
  • Examples: Any type of oil, cinnamon, gasoline.
  • Solubility: Hydrophobic molecules/substances can dissolve into each other.
    • Example: Vegetable oil mixed with olive oil.

Hydrophilic Substances

  • Definition: "Water-loving" chemicals that can dissolve in water and form a solution.
  • Molecular Structure: Include molecules with one or more polar covalent bonds and/or ionic bonds.
  • Solubility: Hydrophilic molecules/substances can dissolve into each other.

Homogeneous Mixtures

  • Definition: Mixtures where the components/chemicals are equally distributed.
    • Example: Salt water (salt/H_2O mixture).

Types of Homogeneous Mixtures

A) Suspensions
  • Definition: When the components of a mixture are temporarily distributed equally.
  • Characteristic: Over time, suspensions eventually become a heterogeneous mixture (components separate).
  • Examples:
    • Salad Dressing: A mix of oil, vinegar, and chunks initially appears homogeneous when shaken but separates into layers (e.g., oil and vinegar) with chunks settling over time.
    • Blood: When first drawn, blood appears homogeneous (components evenly distributed) due to constant mixing in the body.
      • However, after a minute of sitting, it separates into layers: plasma, white blood cells, and red blood cells.
C) Colloids (or "Gels")
  • Definition: A cross between suspensions and solutions; homogeneous mixtures where a compound is partially suspended and partially dissolved.
  • Example: Jello.
    • Jello contains gelatin, which is a protein (also known as collagen).
    • Collagen is the most abundant protein in the body, found in bones, nails, cartilage, skin, etc.
    • Gelatin Molecule Characteristics:
      • Part of the molecule is hydrophilic at all temperatures.
      • Another part is hydrophilic at high temperatures but becomes hydrophobic at low temperatures.

Acids

  • Definition: Chemicals that produce hydrogen cations (H^+) when mixed into a solution.
  • H^+ in Solution: The presence of H^+ ions makes a solution acidic.
  • Example 1: Hydrochloric Acid (HCl)
    • When HCl is mixed into water (H_2O), its ionic bond breaks.
    • It forms hydrogen ions (H^+) and chloride ions (Cl^-).
    • Equation: HCl \xrightarrow{H_2O} H^+ + Cl^-
  • Example 2: Sulfuric Acid (H2SO4)
    • When mixed into water, H2SO4 breaks apart and produces H^+ions.

Buffers

  • Definition: Chemicals that react with hydrogen (H^+) and hydroxide (OH^-) ions, thereby removing them from a solution.
  • Function: When a buffer is added to a solution, it makes the solution neutral, or less acidic or basic.
  • Example: Bicarbonate (HCO_3^-)
    • HCO_3^- is the main ingredient in antacids, also known as "baking soda."
    • Scenario 1: Bicarbonate added to an acidic solution
      • The bicarbonate reacts with excess H^+ ions.
      • Reaction: HCO3^- + H^+ \rightarrow H2O + CO_2
      • This reaction removes H^+ from the solution, making it less acidic (e.g., pH changes from 3 to 6 or 7).
    • Scenario 2: Bicarbonate added to a basic solution
      • The bicarbonate reacts with excess OH^- ions.
      • Reaction: HCO3^- + OH^- \rightarrow H2O + CO_3^{2-}
      • This reaction removes OH^- from the solution, making it less basic.
    • Analogy: Buffers act like a "chemical sponge" that gets rid of H^+ and OH^- ions, maintaining pH stability.

Bases

  • Definition: Chemicals that produce hydroxide anions (OH^-) when mixed into water (H_2O).
  • OH^- in Solution: The presence of OH^- ions makes a solution "basic" (also known as "alkaline").
  • Example 1: Sodium Hydroxide (NaOH)
    • Also known as "lye."
    • When NaOH is mixed into water (H_2O), it separates into Na^+ and OH^- ions floating around.
  • Example 2: Ammonia (NH_3)
    • When NH3 is added to water, it forms NH4^+ and OH^- ions.
    • Reaction: NH3 + H2O \rightarrow NH_4^+ + OH^-
    • This makes the solution basic.

pH Scale

  • Definition: A measure of how acidic or basic a solution is.
  • Range: The pH scale ranges from 0 to 14.
  • pH Values and Characteristics:
    • Acidic Solutions: Have a pH between 0 and 6.9.
      • Contain hydrogen ions (H^+).
      • Increasing H^+ concentration corresponds to decreasing pH (more acidic).
    • Basic (Alkaline) Solutions: Have a pH between 7.1 and 14.
      • Contain hydroxide ions (OH^-).
      • Increasing OH^- concentration corresponds to increasing pH (more basic).
    • Neutral Solutions: Have a pH of 7.0.
      • Have equal amounts of H^+ and OH^- ions, or none at all.
  • Visual Representation:
    • \text{Acidic (0)} \longleftrightarrow \text{Neutral (7.0)} \longleftrightarrow \text{Basic (14)}
    • Increasing H^+ concentration goes towards 0.
    • Increasing OH^- concentration goes towards 14.