Acid –Base Theories 19.1 A. Acids

Describing an Acid  Tastes “sour”  Common compound in fruits and vegetables  corrosive  Forms electrolytes when in aqueous solution (ions!)  Is a molecular compound

Explaining Acid Behavior  Acids are hydrogen containing substances, HCl, H 2 SO 4  But not all hydrogen containing compounds are acids!!! CH 4, C 6 H 12 O 6  Dissociate (ionize) by releasing H+ ions (hydrogen ion or proton) into solution.  written as a dissociation Rx  HCl →H + + OH -

Acid Formulas  Acids are ionic compounds where the cation is H+ (not a metal)  Anion: Periodic table (how many +/-) and Memory (polyatomic ions: nitrate, hydroxide, carbonate, chlorate, sulfate, phosphate  Undissociated it is a neutral compound

Acid Formulas  Example: phosphoric acid  Made of phosphate and enough H+ to neutralize it  Formula of phosphate:  PO 4 3-  Plus 3 H+  H 3 PO 4

Types of Acids Contains/releases one ionizable H+, monoprotic acid  HCl → H+ + Cl- Contains/releases two ionizable H+, diprotic acid  H 2 SO 4 → 2H+ + SO 4 2- Contains/releases three ionizable H+, triprotic acid  H 3 PO 4 → 3H+ + PO 4 3-

Review Electronegativity  Increases in this direction

Why do acids release H+?  H involved in very polar covalent bonds –attached to a very electronegative element are released as H+ ions  Example HCl: Cl is very electronegative H-Cl ---  H + + Cl - δ+ δ- δ+ δ-  On the other hand: CH4 weakly polar molecule: C is not very electronegative, does not release an H+!!!

What does the H+ do?  Reacts with H 2 O to form an hydronium ion H 3 O+ a. H+ + H 2 O → H 3 O +

Hydrochloric acid (hydrogen chloride)  HCl  Monoprotic acid H - Cl H - Cl  HCl → H + + Cl -

Nitric Acid  HNO 3  Monoprotic acid  HNO 3 → H+ + NO 3 -

Carbonic Acid  H 2 CO 3  Diprotic acid  H 2 CO 3 →2 H+ + CO 3 2-

Phosphoric Acid  H 3 PO 4  Triprotic acid  H 3 PO 4 →3 H+ + PO 4 3-

Sulfuric Acid  H 2 SO 4  Diprotic acid  H 2 SO 4 → 2H+ + SO 4 2-

Formulas of Organic Acids- Acids of Hydrocarbons  Example: CH 3 COOH  Not all hydrogens are released!  Which bonds are high/low polar very polar very polar Weak polar  Monoprotic

Organic Acids have Carboxyl Groups  COOH group is called a carboxyl group  Makes a molecule acidic  Dissociation: CH 3 COOH → CH3COO - + H +

Ethanoic Acid (acetic or vinegar acid)  CH 3 COOH  monoprotic acid  CH 3 COOH →H+ + CH 3 COO -

B. Describing a Base  Adjective: basic or alkaline  rare in nature/foods  taste bitter  are part of soaps –make surfaces slippery  Corrosive, often more dangerous than acids  Are part of cleaners, drain openers  Act as electrolyte if aqueous

Base Formulas  Normal ionic neutral compound: metal cation and hydroxide anion (OH-)  Formula ends with OH  Name ends with ‘hydroxide’  NaOH –sodium hydroxide  Give the formula of Calcium Hydroxide  Ca(OH) 2

Base Behavior  Dissociation into metal cation and hydroxide ion, OH-  A base is a hydroxide donor  NaOH → Na+ + OH-

Sodium Hydroxide NaOH  Ionic compound  Releases OH-  NaOH → Na+ + OH-  Other similar base: KOH (potassium hydroxide), CsOH, RbOH

Magnesium hydroxide  Mg(OH) 2  Mg(OH) 2 → Mg (OH) -  Similar are Calcium- or Bariumhydroxide

Ammonia NH3  Exceptional base:  Does not directly release OH-  Instead breaks water apart  NH3 + H2O → NH4+ + OH-

Testing for Acids and Bases  indicator substances that change color  Litmus paper  Commercially available test strips

Acids and Bases together  React with each other  neutralize  form a salt of the base cation and the acid anion and water HCl + NaOH→ NaCl + H2O Practice: Carbonic acid reacts with Calcium hydroxide