Acids, Bases, Salts An introduction

Properties Acids: sour taste, react with some metals to produce hydrogen gas; aqueous solutions of acids are electrolytes Bases: bitter taste, slippery feel; aqueous solutions of bases are electrolytes

Arrhenius acids and bases Acids ionize to yield H+ ions (aq) Bases ionize to yield OH- ions (aq) This is a narrow definition!

Arrhenius acids Acid types: Monoprotic: one ionizable hydrogen Diprotic: two ionizable hydrogens Triprotic: three ionizable hydrogens

Arrhenius bases Most are hydroxides of metals IA salts dissociate well IIA salts dissociate poorly

Bronsted-Lowry Acids and Bases Acid: hydrogen ion donor Base: hydrogen ion acceptor Realization: Bronsted-Lowry and Arrhenius acids/bases are not necessarily the same! Example of base: ammonia: NH3 becomes NH4+

Conjugate acids and bases A conjugate acid is the particle formed when a base gains H+. A conjugate base is the particle that remains when an acid has donated H+. A conjugate acid/base pair consists of two substances related by the gain/loss of H+. Remember: water is a H+ acceptor, so it is a B/L base. Forms hydronium ion, H3O+

Amphoteric substances Substances which can be either an acid or a base Water is amphoteric: can either gain or lose H+

Lewis Acids and Bases Acid: accepts a pair of electrons during a reaction Base: donates a pair of electrons When they do this, a covalent bond forms

Hydrogen Ions and Acidity Self-ionization: water breaking down into H+ and OH- When [H+] = [OH-], pH is neutral. Ion Product Constant: H+ (aq) + OH- (aq)  H2O (l) Kw = [H+][OH-] =1.0x10-14 If an acid, [H+] > 1x10-7 If a base, [H+] < 1x10-7

pH and pOH pH = -log [H+] If pH>7, basic/alkaline If pH<7, acidic pOH = 14 – pH For calculations, use scientific notation!

Measuring pH Indicators: substances which can form both acids and bases in solution, depending upon the concentration of H+ Endpoint: pH where an indicator changes its color pH meters: instruments which measure [H+]

Strengths of Acids and Bases Strong a/b: dissociate completely (form ions totally) in solution Weak a/b: only dissociate/ionize slightly

Strengths of Acids and Bases Acid Dissociation Constant: Keq= [H3O+][A-] [H2O][HA] These are called Ka values, acid dissociation constants. The stronger the acid, the larger the Ka value. Same for bases. Dissociation constants: substitute into formula to find unknowns

Neutralization reactions Acid/base reactions Acid + base -> salt + water Titrations: determine equivalence point, where the moles H+ equal moles OH-. This equalization point is shown with an indicator, discussed earlier, called an endpoint

Salts in Solution Salt Hydrolysis: splitting apart in water Some solutions of salts are neutral, some acidic, some basic.