Acids & Bases - Introduction Lemons fresh eggs lima beans brussel sprouts pH: 2 – 3 12 alkaline Lemons: http://www.indiamart.com/jasinternationalexim/yellow-lemon.html Lima Beans: http://www.alkaline-alkaline.com/ph_food_chart.html) Brussel sprouts: http://www.alkaline-alkaline.com/ph_food_chart.html Acid red – acidic soil base blue – basic soil Acids Bases_INTRO

General Properties of Acids and Bases taste sour taste bitter change plant-dye indicators (litmus = red) change plant-dye indicators (litmus = blue) react with certain metals to produce H2 gas feel slippery react with carbonates and hydrogen carbonates to produce CO2 aqueous solutions conduct electricity pH < 7 pH >7

Litmus (and some other plant pigments – e.g., Hydrangea) B Aci Re ase lue

Common Acids in Everyday Use Name Formula Use hydrochloric acid HCl stomach acid acetic acid HC2H3O2 vinegar nitric acid HNO3 (industry) sulfuric acid H2SO4 car battery carbonic acid H2CO3 seltzer, blood phosphoric acid H3PO4 Coke, Pepsi

HCl(aq)  H+(aq) + Cl–(aq) But because acids & bases occur in water, the actual rxn is: HCl(aq) + H2O(l)  H3O+(aq) + Cl–(aq) H3O+(aq) is called an ‘hydronium ion’ This type of ‘dissociation reaction’ is an ‘ionization reaction’ because it forms ions.

But there’s a problem with Arrhenius’s definitions. Ammonia (NH3). NH3 turns litmus blue. NH3 has a pH > 7 NH3 doesn’t react with metals or carbonates to produce any gas. But according to Arrhenius’s definition: NH3 can’t be a base because it has no ‘O’ (to lose as OH–).

To explain how ammonia (NH3) is a base, Brønsted and Lowry (separately) developed a new definition for bases. (Remember acids & bases occur in water, so water may have a role in the reactions.) NH3 + H2O  NH4+ + OH– Formation of the hydroxide ion (OH–) is what makes ammonia (NH3) a base! (Often called the Brønsted-Lowry definition)

Strong vs. Weak Acids & Bases Strong Acids & Bases: Completely Ionize Strong Acid: HCl(aq)  H+(aq) + Cl–(aq) In the sol’n: no HCl; only H+ and Cl– Equation: HCl(aq)  H+(aq) + Cl–(aq) Actual Sol’n: H+(aq) + Cl–(aq)

Weak Acids & Bases: Don’t Completely Ionize Weak Acid: HF(aq)  H+(aq) + F–(aq) in the sol’n: HF and H+ and F– Equation: HF(aq) H+(aq) + F–(aq) Actual Sol’n: HF(aq) H+(aq) + F–(aq)

Strong Acids & Bases - Completely Ionize HCl Group 1 – LiOH HBr NaOH HI KOH HClO4 Group 2 (heavy members) HNO3 Ca(OH)2 H2SO4 Sr(OH)2 Ba(OH)2

Concentrated or Dilute Acids & Bases Refers to the quantity of the acid or base in the solution. Example: 0.001 M HCl is a strong acid but it is a dilute (not a concentrated) solution at this molarity. 23 M HF is a concentrated solution at this molarity but it is still a weak acid.

Amphoteric = can act as either an acid or base. Commonly occur in di- and triprotic acids: Diprotic acid: H2SO4 The first proton (1): H2SO4 + H2O H3O+ + HSO4– The second proton (2): HSO4– + H2O H3O+ + SO42– The intermediate (HSO4–) is amphoteric and can act as either a base (1; accepts H+ from H3O+) or acid (2; donates H+ to H2O)

What would be the ionization for a triprotic acid? (1) H3PO4 + H2O H2PO4– + H3O+ (2) H2PO4– + H2O HPO42– + H3O+ (3) HPO42– + H2O PO43– + H3O+ Which species is amphoteric? H3PO4