Acids & Bases I

Characteristics of Acids and Bases

• Both produce ions when dissolved in water

  • They form ionic solutions that conduct electricity (Electrolytes)

• Acids:

  • taste SOUR

  • conduct electricity

  • turn litmus paper RED

  • produce H⁺ _(g) when reacted with certain metals (ex. Mg²⁺)

  • neutralized by bases

• Bases:

  • taste BITTER

  • conduct electricity

  • turn litmus paper BLUE

  • feel slippery

  • neutralized by acids

Arrhenius Theory

• Acid (Ends in H⁺) = any compound that produces H⁺ _(aq) ions in water

• Base (Ends in OH^-) = any compound that produces OH^- _(aq) ions in water

• Salts = any other compound that’s not an acid or base

• Neutralization reaction: Acid + Base → Salt + Water

Hydronium

• When acids dissolve in water, they produce an H⁺ _(aq) ion

• Protons don’t exist alone in water, they create hydronium, H₃O⁺_(aq)

Bronsted-Lowry Theory

• Explains the existence of EQUILIBRIUM reactions (not considered in Arrhenius theory)

• Acid = any substance that can DONATE a proton to another substance

• Base = any substance that can ACCEPT a proton to another substance

• Forms conjugate pairs in reaction: acid + base ⇌ base + acid

Conjugate Acid-Base Pairs

• Ex. HCN (acid) + H₂O (base) ⇌ H₃O⁺ (conjugate base) + CN^- (conjugate acid)

• Forward reaction:

  • HCN acts as an acid, loses an H⁺ and +1 charge to become CN^-

  • H₂O acts as a base, gains a H⁺ and +1 charge to become H₃O⁺

• Reverse reaction:

  • H₃O⁺ acts as the acid

  • CN^- acts as the base

• Conjugate acid-base pairs differ by ONE proton

  • Conjugate ACID: has an EXTRA proton

  • Conjugate BASE: LACKS a proton

Amphiprotic Substances

• Can act as either an acid or a base depending on the kind of substances they react with

  • Possesses a NEGATIVE charge

  • Has an easily removable H⁺

    • All except H⁺ attached to C

Polyprotic Acids

• Acids that can donate:

  • ONE proton = MONOprotic

  • TWO protons = DIprotic

  • THREE protons = TRIprotic

  • more than ONE proton = POLYprotic

Strengths of Acids & Bases

• The relative strength of an acid or a base depends on how well it ionizes with water to produce ions

• STRONG acids & bases completely 100% ionize

• WEAK acids & bases partially ionize, better represented by equilibrium system

• Strength does not refer to molar concentration

  • 0.0010 M HCl is a STRONG acid

  • 6.0 M HF is a WEAK acid

Strong Acids & Bases

• STRONG acids: HBr, HCl, HI, HNO₃, HClO₄, H₂SO₄ (one way arrows)

• STRONG bases: O₂^-, NH₂^- (one way arrows)

  • Protonates ASAP: O₂^- + H₂O → 2OH^- and NH₂^- + H₂O → NH₃ + OH^-

    • Do NOT exist as conjugate acids, cannot donate proton to water

• Other STRONG bases: LiOH, NaOH, KOH, Sr(OH)₂, Ca(OH)_2, Ba(OH)₂

  • Can stably exist in water

Weak Acids & Bases

• Weak acids: HIO₃ to H₂O

  • OH^- and NH₃, cannot act as acids in aqueous solutions

• Weak bases: H₂O to PO₄^3-

  • HSO₄^-, NO₃^-, Cl^-, Br^-, I^-, ClO₄^-, cannot act as bases in aqueous solutions

• HPO₄^2- and HCO₃^- can be found on both sides of table

  • They are amphiprotic and can act as both weak acids and bases

Levelling Effect

• All strong acids and bases have IDENTICAL strengths in water because they are all 100% ionized in aqueous solutions

Salt Hydrolysis

• Reaction between water & the cation or anion (or both) contained in the salt to produce an acidic or basic solution

• ANIONIC hydrolysis (Forms basic solution):

  • If the anion of a salt hydrolyzes, it acts as a BASE in water to accept a proton and produce OH^- _(aq)

• CATIONIC hydrolysis (Forms acidic solution:

  • If the cation of a salt hydrolyzes, it acts as an ACID in water to donate a proton and produce H₃O⁺ _(aq)

• STRONG ACID - STRONG BASE → NEUTRAL

• STRONG ACID - weak base → ACIDIC

• weak acid - STRONG BASE → BASIC

Spectator Ions

• Do not participate in the reaction, do not hydrolyze

• Cations (+):

  • Alkali metals (group 1), alkaline earth metals (group 2)

• Anions (-):

  • Conjugate bases of strong acids (ex. I^-)

• HSO₄^- is not a spectator ion, it’s a weak acid