1. 8.1 EXPLAINING THE PROPERTIES OF ACIDS & BASES SCH4U - Chemistry, Gr. 12, University Prep Mr. Dvorsky

2. Common Properties of Acids & Bases PropertyAcidBase TasteSourBitter Texture of SolutionNo characteristic textureSlippery Aqueous Property of Oxides Non-metal oxides form acidic solutions: CO 2(g) + H 2 O (l)  H 2 CO 3(aq) Metal oxides form basic solutions: CaO (g) + H 2 O (l)  Ca(OH) 2(aq) Reaction with PhenolphthaleinColourlessPink Reaction with litmus paper Blue litmus  RedRed litmus  Blue Reaction with Metals Acids react with metals above H in the activity series to displace H 2(g) Bases react with certain metals (i.e. Al) to form H 2(g) Reaction with CO 3 2- Form CO 2(g) No reaction Reaction with NH 4 ClNo reactionForm NH 3 Reaction with Fatty AcidsNo reaction React to form soap (saponification reaction) Neutralization Reactions Acid + Base  Water + Salt

3. Arrhenius Theory of Acids & Bases (Arrhenius, 1887)  Acids & bases are defined in terms of their structure and the ions produced when they dissolve in water.  Explains acid-base reactions and neutralization.  ACID: dissociates in water to form H + (aq) HCl (hydrochloric acid), H 2 SO 4 (sulphuric acid)  BASE: dissociates in water to form OH - (aq) NaOH (sodium hydroxide), KOH (potassium hydroxide)  LIMITATIONS:  hydrogen ion combines with water to form hydronium ion  does not explain some bases (i.e. ammonia, salt solutions)  does not explain acid-base reactions without water (i.e. gas)

4. Brønsted-Lowry Theory (Johannes Brønsted & Thomas Lowry, 1923)  Recognizes an acid-base reaction as chemical equilibrium, have a forward and reverse reaction involving the transfer of a proton  ACID: substance from which a proton can be removed “proton-donor”  BASE: substance that can accept a proton “proton-acceptor” proton = nucleus of a hydrogen atom (H + ion) acid base conjugate conjugate acid base

5. Conjugate Acid-Base Pairs  dissociation is an equilibrium reaction because it proceeds in both directions  H 2 O donates a proton in forward rxn  acid  OH - accepts a proton in reverse rxn  conjugate base  If a substance acts as a proton donor and a proton accepter, it is termed “amphoteric” (i.e. water) base acid conjugate conjugate acid base

6. Strong Acids  Completely dissociates in water (equilibrium favours products, lies to the right)  Binary acids [HX (aq) where X = Cl, Br, I (not F)] Factors: Across period: electronegativity Down a group: bond strength  Oxoacids (contain oxygen atoms) where the # [O] > # H (by 2 or more) Factors: Number of oxygen atoms  Monoprotic only have single H atom that dissociates  Polyprotic have more than 1 H atom that dissociates Strength decreases as number of hydrogen atoms that have dissociated increases

7. Strong Bases  Completely dissociates in water (equilibrium favours products, lies to the right)  Oxides & Hydroxides of alkali metals (Group 1) and of of alkali earth metals (Group 2) below beryllium [e.g. NaOH sodium hydroxide, MgO magnesium oxide] Factors: Metals with low electronegativity form ionic bonds with oxygen  easily break bond with oxygen which reacts with water to form hydroxide ions

8. Calculations that involve strong acids & bases  Strong acids/bases (and strong electrolytes) completely dissociates into ions in water  [H 3 O] + (aq) is equal to the [strong acid]  [OH] - (aq) is equal to the [strong base]  You cannot determine the concentrations of ions of weak acids/bases/electrolytes this way because they do not completely dissociate in solution (more next class)