Acids and Bases

Arrhenius’ Definition Acids give H+ when dissolved in water. Bases give OH- when dissolved in water.

Acid or Base? The measure of the concentration of H+ ions in a solution is called pH The pH scale measures how acidic or basic a solution is The scale ranges from -1 to 14 -1 = extremely strong acid 14 = extremely strong base

pH Examples

Metal + Acid  Salt + H2(g) Acid + Base  Salt + H2O(l) Properties of Acids Affects the color of indicators. React with metals to produce hydrogen gas. Metal + Acid  Salt + H2(g) Neutralization of bases to form water. Acid + Base  Salt + H2O(l) Taste sour Citris fruits, vinegar, sour milk are all composed of acids.

Strong and Weak Acids Strong acids will completely dissociate. (all of molecules become ions) HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq) Weak acids do not dissociate easily. (only a few molecules become ions) HC2H3O2(aq) + H2O(l)  H3O+(aq) + C2H3O2-(aq) H3O+ = Hydronium (same thing as H+) Notice the H+ bonds with the H2O to form H3O+.

Examples of Acids Strong Acids HCl Hydrochloric acid HBr Hydrobromic acid HI Hydroiodic acid HNO3 Nitric acid H2SO4 Sulfuric acid HClO3 Chloric acid HClO4 Perchloric acid

Examples of Acids Weak Acids H2CO3 Carbonic acid HC2H3O2 Acetic acid Citric Acid H2O

Mono and Polyprotic acids Monoprotic Acids Poly = many These acids donate more than one H+ (per molecule) when they dissociate Polyprotic acids ionize in steps H2S  H+ + HS- HS-  H+ + S-2 H3PO4  H+ + H2PO4- H2PO4-  H+ + HPO42- HPO42-  H+ + PO43- Mono = 1 These acids donate one H+ (per molecule) when they dissociate HCl  H+ + Cl- HNO3  H+ + NO3-

Acid + Base  Salt + H2O(l) Properties of Bases Affects the color of indicators. Neutralization of acids to form water. Acid + Base  Salt + H2O(l) Taste bitter. (NaHCO3 – Baking Soda) Feel slippery.

Strong and Weak Bases Strong bases: yield OH- in solution. Group 1a: LiOH, NaOH, KOH, RbOH, CsOH Group 2a: Ca(OH)2 , Sr(OH)2 , Ba(OH)2 Weak bases do not dissociate in solution, they just accept a H+ NH3, H2O, CO32-, HClO- Many others

Bronsted-Lowry Definition Acids are any substance that can donate an H+. Bases are any substance that can accept an H+. HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) Acid Proton Donor Base Proton Acceptor

HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) Conjugate Pairs Reversible reactions have an acid and base on both sides Pairs that differ by only one proton (H+) are called conjugate pairs HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) Acid Base Conjugate Acid Conjugate Base

A strong acid will make a weak conjugate base A weak acid will make a strong conjugate base. Same for strong & weak bases.

What about H2O? Acid or Base? HCl(g) + H2O(l)  H3O+(aq) + Cl-(aq) Acid Base Conjugate Acid Conjugate Base NH3(g) + H2O(l)  NH4+(aq) + OH-(aq) Conjugate Acid Acid Conjugate Base Base

Water is amphoteric Amphoteric means a substance can either accept a proton (base) or donate a proton (acid). Water will act as a base when in solution with an acid Water will act as an acid when in solution with a base