Acids & Bases - Introduction a.Acids Bases_INTRO

General Properties of Acids and Bases AcidsBases taste sourtaste bitter change plant-dye indicators (litmus = red)change plant-dye indicators (litmus = blue) react with certain metals to produce H 2 gasfeel slippery react with carbonates and hydrogen carbonates to produce CO 2 aqueous solutions conduct electricity pH < 7pH >7

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

Common Acids in Everyday Use NameFormula Use hydrochloric acidHClstomach acid acetic acidHC 2 H 3 O 2 vinegar nitric acidHNO 3 (industry) sulfuric acidH 2 SO 4 car battery carbonic acidH 2 CO 3 seltzer, blood phosphoric acidH 3 PO 4 Coke, Pepsi

HCl (aq)  H + (aq) + Cl – (aq) But because acids & bases occur in water, the actual rxn is: HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl – (aq) H 3 O + (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 (NH 3 ). 1.NH 3 turns litmus blue. 2.NH 3 has a pH > 7 3.NH 3 doesn’t react with metals or carbonates to produce any gas. But according to Arrhenius’s definition: NH 3 can’t be a base because it has no ‘O’ (to lose as OH – ).

To explain how ammonia (NH 3 ) 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.) NH 3 + H 2 O  NH OH – Formation of the hydroxide ion (OH – ) is what makes ammonia (NH 3 ) a base! (Often called the Brønsted-Lowry definition)

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

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

Strong Acids & Bases - Completely Ionize AcidsBases HClGroup 1 – LiOH HBr NaOH HI KOH HClO 4 Group 2 (heavy members) HNO 3 Ca(OH) 2 H 2 SO 4 Sr(OH) 2 Ba(OH) 2

Concentrated or Dilute Acids & Bases Refers to the quantity of the acid or base in the solution. Example: M HCl is a strong acid but it is a dilute (not a concentrated) solution at this molarity. Example: 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: The second proton (2):HSO 4 – + H 2 O H 3 O + + SO 4 2 – The first proton (1):H 2 SO 4 + H 2 O H 3 O + + HSO 4 – The intermediate (HSO 4 – ) is amphoteric and can act as either a base (1; accepts H + from H 3 O + ) or acid (2; donates H + to H 2 O) Diprotic acid: H 2 SO 4

What would be the ionization for a triprotic acid? H 3 PO 4 (2) H 2 PO 4 – + H 2 O HPO 4 2– + H 3 O + (1)H 3 PO 4 + H 2 O H 2 PO 4 – + H 3 O + (3) HPO 4 2 – + H 2 O PO 4 3– + H 3 O + Which species is amphoteric?