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Acids: react with zinc, magnesium, or aluminum and form hydrogen (H 2(g) )

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Acids: react with zinc, magnesium, or aluminum and form hydrogen (H 2(g) )

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  1. Three models of acids:l. Arrhenius Model Basis for the model--action in water acid definition: produces H in water solution base definition: produces OH1- in water solution 2. Bronsted-Lowry Model Basis for the model-- proton transfer acid definition: donates a proton ( H ) base definition: accepts a proton conjugate acid definition: the acid becomes the conjugate base after it donates the proton because it can now accept it back. conjugate base definition: the base becomes the conjugate acid after it accepts the proton because it can now donate it back. 3. Lewis ModelBasis for model--electron pair transfer acid definition: accepts a pair of electrons base definition: donates a pair of electrons

  2. Acids: • react with zinc, magnesium, or aluminum and form hydrogen (H2(g)) • react with compounds containing CO32- and form carbon dioxide and water • turn litmus red • taste sour (lemons contain citric acid, for example) DO NOT TASTE ACIDS IN THE LABORATORY!! Bases: • feel soapy or slippery • turn litmus blue • they react with most cations to precipitate hydroxides • taste bitter (ever get soap in your mouth?) DO NOT TASTE BASES IN THE LABORATORY!!

  3. Water dissociation: H2O(l)  →  H+(aq) + OH-(aq) Definitions of acidic, basic, and neutral solutions based on [H+] • acidic: if [H+] is greater than 1 x 10-7 M basic: if [H+] is less than1 x 10-7 Mneutral: if [H+] if equal to 1 x 10-7 M

  4. pH • relationship between [H+] and pH • pH = -log10[H+] • Definition of acidic, basic, and neutral solutions based on pH • acidic: if pH is less than 7 basic: if pH is greater than 7 neutral: if pH is equal to 7

  5. Acids 1. Strong Acids: • completely dissociate in water, forming H+ and an anion. example: HN03 dissociates completely in water to form H+ and N031-. • The reaction is • HNO3(aq)  →   H+(aq) + N031-(aq) • There are only 6 strong acids. The remainder of the acids therefore are considered weak acids. • HCl • H2SO4 • HNO3 • HClO4 • HBr • HI • Note: when a strong acid dissociates only one H+ ion is removed. H2S04 dissociates giving H+ and HS04- ions. • H2SO4  →   H+ + HSO41- 2. Weak acids: • a weak acid only partially dissociates in water to give H+ and the anion for example, HF dissociates in water to give H+ and F-. It is a weak acid. with a dissociation equation that is • HF(aq)  ↔   H+(aq) + F-(aq) • Note the use of the double arrow with the weak acid. That is because an equilibrium exists between the dissociated ions and the undissociated molecule. In the case of a strong acid dissociating, only one arrow (  →  ) is required since the reaction goes virtually to completion.

  6. 1. Strong Bases: • They dissociate 100% into the cation and OH- (hydroxide ion). • example:  NaOH(aq)  →   Na+(aq) + OH-(aq) • Which are the strong bases? The hydroxides of Groups I and II. 2. Weak Bases: • What compounds are considered to be weak bases? • Most weak bases are anions of weak acids. • Weak bases do not furnish OH- ions by dissociation. They react with water to furnish the OH- ions. • When a weak base reacts with water the OH- comes from the water and the remaining H+ attaches itsef to the weak base, giving a weak acid as one of the products. You may think of it as a two-step reaction similar to the hydrolysis of water by cations to give acid solutions. examples: • NH3(aq) + H2O(aq)  →   NH4+(aq) + OH-(aq) • methylamine: CH3NH2(aq) + H20(l)  →   CH3NH3+(aq) + OH-(aq) • acetate ion: C2H3O2-(aq) + H2O(aq)  →  HC2H302(aq) + OH-(aq) • General reaction: weak base(aq) + H2O(aq)  →   weak acid(aq) + OH-(aq) • Since the reaction does not go to completion relatively few OH- ions are formed.

  7. Acid-Base Reactions: • Strong acid + strong base:   HCl + NaOH  →   NaCl + H2O salt +water produced

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