Acids and bases

Lewis Acids & Bases

Definition

An acid is an electron pair acceptor

A base is an electron pair donor

  • Protonated form – proton (available to donate) is on the molecule.

  • Deprotonated form – proton is off the molecule.

Common bases

  • Sodium bicarbonate (NaHCO3) – baking soda; antacid; source of CO2

  • Sodium carbonate (Na2CO3) – soap production; general cleaner; water softener

  • Potassium hydroxide (KOH) – soap production; batteries; electroplating

  • Sodium hydroxide (Lye) (NaOH) – petroleum processing; soap & plastic manufacturing

  • Ammonia (NH3) – detergent; fertilizer; explosive manufacturing

  • Magnesium hydroxide (Mg(OH)2) – milk of magnesia (laxative for constipation)

  • Aluminum hydroxide (Al(OH)2) – antacid (relieves heartburn & indigestion)Sodium bicarbonate (NaHCO3) – baking soda; antacid; source of CO2

  • Sodium carbonate (Na2CO3) – soap production; general cleaner; water softener

  • Potassium hydroxide (KOH) – soap production; batteries; electroplating

  • Sodium hydroxide (Lye) (NaOH) – petroleum processing; soap & plastic manufacturing

  • Ammonia (NH3) – detergent; fertilizer; explosive manufacturing

  • Magnesium hydroxide (Mg(OH)2) – milk of magnesia (laxative for constipation)

  • Aluminum hydroxide (Al(OH)2) – antacid (relieves heartburn & indigestion)

Properties Shared by BOTH Acids & Bases

  • Aqueous (water based) acid-base solutions conduct electricity because electrolytes/ions are formed in solution

    • In water, acids generally produce H+ (hydrogen ions / protons) which reacts with water to form H3O+ (hydronium ions), while bases generally produce OH– (hydroxide ions).

  • When acids and bases are reacted together they form salts and water

Acids

  • Taste sour

  • pH < 7

  • Changes litmus paper

    • Blue to Red (or Red remains Red)

  • Corrosive (damages materials)

  • Produce H2 upon reaction with active metals (e.g., alkali metals, alkaline earth metals, zinc, aluminum)

  • Produces H2O & CO2 upon reaction with carbonates


    Bases

    • Taste bitter; chalky

    • pH > 7

    • Changes litmus paper

      • Red to Blue (or Blue remains Blue)

    • Caustic (damages materials & skin)

    • Feels slippery or soapy

To name an acid:

–ate is replaced with “–ic acid”

–ite is replaced with “–ous acid”

–ide is replaced with “hydro__ic acid”

  • In sulphur compounds add “ur” followed by the above rules

  • In phosphorus compounds add “or” followed by the above rules

Two substances which differ only by the presence or absence of a H+ (proton), make a conjugate acid-base pair.

  • An amphoteric compound is a substance that can react as both an acid or base (depending on the reaction)

  • pH scale is a way of expressing the concentration of acids and bases.

    • pH < 7 = acidic

    • pH = 7 neutral (for pure water at 25 °C)

    • pH > 7 = basic

  • pH is determined by the concentration of hydrogen ions [H+] 

    • In aqueous solutions, the [H3O+]

  • Water has a pH of 7 (at 25 °C) which is common referred to as neutral.

Temperature affects pH! 

  • Red Litmus Paper

    • When exposed to BASE turns it BLUE

    • When exposed to ACID, it stays RED

  • Blue Litmus Paper

    • When exposed to ACID, it turns RED

    • When exposed to BASE, it stays BLUE

  • Wide Range pH Paper

    • Changes color based on pH

    • Compare the paper’s color change (final color) to the included color scale to estimate pH

    • Dissociate

    • Ionize

    • Monoprotic

    • Polyprotic

      • Diprotic

      • Triprotic

      Strong Acids

      • HCl (hydrochloric acid)

      • HBr (hydrobromic acid)

      • HI (hydroiodic acid)

      • HNO3 (nitric acid)

      • H2SO4 (sulfuric acid)

        • Only the 1st proton is strong, HSO4– is a weak acid

      • HClO3 (chloric acid)

      • HClO4 (perchloric acid)

Strong Bases

  • LiOH (lithium hydroxide)

  • NaOH (sodium hydroxide)

  • KOH (potassium hydroxide)

  • RbOH (rubidium hydroxide)

  • CsOH (cesium hydroxide)

  • Sr(OH)2 (strontium hydroxide)

  • Ca(OH)2 (calcium hydroxide)

  • Ba(OH)2 (barium hydroxide)

Strong = 100% dissociation / ionization

Weak < 100% dissociation / ionization


Acid-base neutralization reactions result in salt and water.

When equal moles of [H+] and [OH–] are mixed together:

Acid + Base ⟶ Saltionic compound + H2O


titrations-Known concentration and volume of one substance to determine the unknown concentration (but known volume) of a second substance.

  • A titration is a lab technique where a known concentration (titrant) is used to determine the concentration of unknown solution (analyte).

  • Typically, the titrant (the known solution) is added to the buret.

  • Using the stopcock on the buret, titrant is added to a known volume of analyte of unknown concentration.