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Explaining the Properties of Acids & Bases

SCH4U - Chemistry, Gr. 12, University Prep. Explaining the Properties of Acids & Bases. Common Properties of Acids & Bases. Acids & bases are defined in terms of their structure and the ions produced when they dissolve in water. Explains acid-base reactions and neutralization.

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Explaining the Properties of Acids & Bases

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  1. SCH4U - Chemistry, Gr. 12, University Prep Explaining the Properties of Acids & Bases

  2. Common Properties of Acids & Bases

  3. 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), H2SO4 (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) Arrhenius Theory of Acids & Bases (Arrhenius, 1887)

  4. 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” Brønsted-Lowry Theory(Johannes Brønsted & Thomas Lowry, 1923) proton = nucleus of a hydrogen atom (H+ ion) acid base conjugate conjugate acid base

  5. dissociation is an equilibrium reaction because it proceeds in both directions • H2O 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) Conjugate Acid-Base Pairs base acid conjugate conjugate acid base

  6. 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 Strong Acids

  7. 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 Strong Bases

  8. Strong acids/bases (and strong electrolytes) completely dissociates into ions in water • [H3O]+(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) Calculations that involve strong acids & bases

  9. Please re-read Section 8.1(pp.528-531) and answer: • p.532 Q.1-3 Done in class Homework

  10. McGraw-Hill Ryerson Chemistry 12 References

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