Acids and Bases Everyday Chemistry! IVORY

Properties of Acids and Bases have a sour taste. (Remember, never taste a chemical in the lab!) react with many metals to produce H2 (g). conduct electricity. turn litmus paper red. start with H (HCl, HNO3, H2SO4, etc.) Examples?

Properties of Bases IVORY Bases: are sometimes called alkalis have a bitter taste. (Again, no tasting!) are generally smooth and slippery feeling. do not react with metals. conduct electricity. turn litmus paper blue. often (but not always) end in -OH (hydroxide). Examples? IVORY

The pH Scale Acids have a pH from 0-6.9 Bases have a pH from 7.1-14 Neutral solutions have a pH of 7.0 pH is based on the amount of H+ ion in a solution.

What’s “H+” got to do with it? There are two definitions for acids and bases. The Arrhenius Definitions: Acid - a substance that dissociates to produce hydrogen ions (H+) in water. ex. HCl(aq) --> H+(aq) + Cl-(aq) Base - a substance that dissociates to produce hydroxide ions (OH-) in water. ex. NaOH(aq) --> Na+(aq) + OH-(aq)

Definition #2 BrØnsted - Lowry Definition H+ is a naked proton (no electrons), so: Acid - Any substance that can donate H+ ions. A proton donor. ex. H2SO4 (aq) --> H+ (aq) + HSO3- (aq) Base - Any substance that can accept H+ ions. A proton acceptor ex. NH3(g) + H2O(l) --> NH4+(aq) + OH-(aq)

Water--Acid or Base? neutral base? acid? It can behave like an acid and a base-amphoteric Lose an H+ to become a hydroxide ion (OH-) Gain an H+ to become a hydronium ion (H3O+) 2H2O (l)  H3O+(aq) + OH-(aq) neutral base? acid?

pH Calculations [H+] [OH-] pH is based on the concentration of H+ ion in a solution. The formula is: pH = -log[H+] Or it may be rearranged to: [H+] = 10-pH (10 to the power of -pH) So, since pure water has pH = 7: [H+]H2O = 1.0 x 10 -7 M Acid------Neutral-----Base [H+] [OH-] 0---------------7------------14

Example Calculations The concentration of hydrogen ions in a solution is 5.21 x 10-2 M. What is its pH? pH = -log[H+] = -log(5.21 x 10-2 M) = 1.28 Calculate [H+] for a solution with a pH of 8.32. [H+] = 10-pH = 10-8.32 = 4.8 x 10-9 M

Strong & Weak Acids Strong Acid - an acid that dissociates fully into ions: HA(aq)  H+(aq) + A-(aq) ex. hydrochloric acid , sulfuric acid, nitric acid Weak Acid - an acid that has an equilibrium with both the original acid compound and ions: HA (aq)  H+(aq) + A-(aq) ex. acetic acid, carbonic acid, phosphoric acid

Strong & Weak Bases Strong Base - a base that dissociates fully into ions: BOH(aq)  B+(aq) + OH-(aq) ex. sodium hydroxide, potassium hydroxide, ammonia (B-L base--written differently) Weak Base - an base that has an equilibrium with both the original base compound and ions: BOH(aq)  B+(aq) + OH-(aq) ex. calcium hydroxide

Acid + Base ==> ?? Acids and bases neutralize each other. When equal amounts of H+ and OH- come together, they make H2O! Acid + Base --> Salt + Water ex. HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O(l) Acid plus a Base make a Salt plus Water!

Buffers Buffers: A buffer is a mixture of chemicals that resists a change in pH. Therefore, a buffer is at a “set” pH. These contain weak acids and their salts. There are buffers keeping your blood at pH = 7.3-7.5

Indicators A chemical that shows whether something is an acid or base by changing color over a relatively narrow pH range. ex. Phenolphthalein -- used in alkali metals experiment; showed that the water turned basic by turning pink ex. Natural indicators: Hydrangeas (see picture), brewed tea, cabbage juice

What else are we doing in this unit? Naming Acids and Bases Calculating pH, pOH, [H+], [OH-] Write neutralization reactions IVORY