Chemistry Joke THE BASE IS UNDER A SALT!
Acids and bases • Acids and bases are two classes of chemical compounds that we encounter frequently in everyday living. • Vinegar and lemon juice are common acids. • Ammonia and bleach are common bases. • Acids and bases have opposite properties and the ability to cancel or neutralize each other. • Almost all acids begin with H+, and most bases end with OH-.
Properties of acids • Taste sour • Are strong or weak electrolytes • React with bases to form water and salts • React with active metals to produce H2 • Turn litmus (and cabbage) red • Low pH
Properties of bases • Taste bitter • Are strong or weak electrolytes • React with acids to form water and salts • Feel slippery • Turn litmus (and cabbage) blue • High pH
Two Acid/Base Theories • Bronsted-Lowry • Arrhenius
Arrhenius • Simplest definition and most restrictive • Acids supply H+ ions • Bases supply OH- ions
Bronsted-Lowry • Added to Arrhenius definition of bases • Acids are proton (H+) donors But… • Bases are proton (H+) acceptors • Don’t necessarily have to supply OH- • NH3 (ammonia) can now be recognized as a base.
Conjugate Acid/base Pairs • Bronsted-Lowry also defined conjugate acids and bases. • HA + H2O A− + H3O+ • HA is an acid. The product A- is its conjugate base. • H2O is behaving as a base. The product H3O+ is its conjugate acid. • These pairs differ by only one H+. • The compound with the extra H+ is the acid.
Self-ionization of water • Sometimes when water molecules collide, a hydrogen ion transfers. • H20 + H20 H3O+ + OH- • Hydronium ion • Hydroxide ion • Sometimes the self-ionization of water is shown as: H20(l) H+(aq)+ OH-(aq) • H+ andH3O+ are often used interchangeably. • Water can act as both an acid and a base, producing both H+ and OH- ions.
Strong acids and Bases • Strength in acids and bases does NOT refer to how corrosive or dangerous they are. • Strong acids and bases dissociate (break apart) completely in water. • At equilibrium, there is no acid or base left that has not ionized (separated into its ions) • One of the most corrosive and dangerous acids, HF, is actually a weak acid.
Strong vs. weak • http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s1/acm2s1_1.htm
Acid / Base neutralization • When an acid reacts with a base, both are neutralized as water and a salt are produced. • Predict the products and write the balanced equation for the reaction of sulfuric acid with potassium hydroxide.
Chemistry Joke • Q: Why do chemistry professors like to teach about ammonia? A: Because it’s very basic material!