When we think of acids and bases we tend to think of chemistry lab acids and bases like But we are surrounded by acids and bases in the world. Most of them are weak. Acids cause: lemons to be sour Acid rain to eat away at sculptures Framed paintings to be damaged Eat cavities in your teeth Digest food in your stomach Fight off other invading ants

Properties of an Acid  Tastes sour  Turns litmus paper red  Has a pH of less than 7  Lemon juice and vinegar are good examples. Properties of a Base  Turns litmus paper blue  Has a pH greater than 7  taste bitter and have a slippery feel  Bases that are soluble (dissolve in water) are called alkalis Most hand soaps and drain cleaners are bases What is an Acid and a Base?

Acids and Bases Arrhenius Bronsted - Lowry pH Acids produce hydrogen ions in aqueous solutions Bases produce hydroxide ions Acids are proton (H + ) donors Bases are proton acceptors Strengths of acids & bases pH = -log [H + ] Lewis acids accept a pair of electrons to form a covalent bond

The Bronsted-Lowry model: An acid is a proton donor (H + ) and a base is proton acceptor HA (aq) +H 2 O (l)  H 3 O + (aq) +A - (aq) acidbase HCl (aq) +H 2 O (l)  H 3 O + (aq) + Cl - (aq) acidbase

An acid will donate a proton. The proton is the H + ion. Remember that a H atom has 1 electron and 1 proton and NO neutrons. So H + is just a proton. This proton that is released by the acid forms a bond with water to form the hydronium ion, H 3 O +.

A base is proton acceptor A- (aq) +H 2 O (l)  HA (aq) +OH - (aq) baseacid NH 3 (aq) +H 2 O (l)  NH 4 + (aq) +OH - (aq) baseacid

Conjugate acid-base pairs When you dissolve an acid in water, the acid donates a proton to a water molecule to form a new acid (conjugate acid) and a new base(conjugate base) HA (aq) +H 2 O (l)  H 3 O + (aq) +A - (aq) acidbaseconjugateconjugate acidbase The conjugate base is what is left over from the acid when it has lost its proton. A conjugate acid-base pair, are the two substances related to each other by the loss and gain of protons.

Which is the acid and which is the base in these equations? HCl (aq) +H 2 O (l)  H 3 O + (aq) +Cl - (aq) NH 3 (aq) +H 2 O (l)  NH 4 + (aq) +OH - (aq) acid Conjugate acid baseConjugate base base Conjugate base acid Conjugate acid

Write conjugate acid / base pairs for the following: a. HClO 4 b. H 3 PO 4 c. H 2 SO 4 d. CH 3 NH 3 + Which of the following are acid-base pairs? a. H 2 O, H 3 O + b. OH -,HNO 3 c. HC 2 H 3 O 2, C 2 H 3 O 2 - d. H 2 SO 4, SO 4 2- ClO 4 - H 2 PO 4 - HSO 4 - CH 3 NH 2 Yes No Yes no

HCl + NH 3  NH Cl - AcidBaseconjugateconjugate acid base Acid / Base pair Cl - is the conjugate base of the acid HClHCl / Cl - NH 4 + is the conjugate acid of the base NH 3 NH 4 + / NH 3

Acid Strength When we dissolve most ionic substances in water they break up into their individual ions. NaCl (s) + H 2 O (aq)  Cl - (aq) + Na + (aq) Most molecules don’t break up into ions. For example sugar. C 12 H 24 O 12 (s) + H 2 O (aq)  C 12 H 24 O 12 (aq) But some molecules do break up into ions. Acids and bases are examples. HCl (l) + H 2 O (aq)  Cl - (aq) + H 3 O + (aq)

This reaction goes almost to completion, which means that there are almost no HCl molecules in the solution. It has fully dissociated into its ions. A strong Acid is one that fully dissociates. The reaction goes to completion CH 3 COOH (aq) + H 2 O (aq)  CH 3 OO - (aq) + H 3 O + (aq) acetic acid wateracetate hydronium ion This is an equilibrium reaction, which in this case is sitting mostly on the left. But not all acids do this. Some weak acids don’t fully dissociate into ions. HCl (aq) +H 2 O (l)  H 3 O + (aq) + Cl - (aq) acidbase

Graphs showing concentrations in acidic solutions

All acid molecules do dissociate And a lot of conjugate bases The solution has a lot of hydronium ions

A weak acid only partially dissociates into its ions Most acid molecules don’t dissociate Only a few hydronium ions form Only a few conjugate bases form

Acid strength and conjugate bases: If you have a strong acid, then its conjugate base will be weak. HNO 3 + H 2 O  NO H 3 O + If you have a weak acid, then its conjugate base will be strong. CH 3 COOH (aq) + H 2 O (aq)  CH 3 OO - (aq) + H 3 O + (aq) Some Strong Acids: H 2 SO 4, HCl, HNO 3, HClO 4, HBr, HClO,

Diprotic Acids: These are acids that can donate 2 protons, like sulfuric acid, H 2 SO 4 H 2 SO 4 (aq) +H 2 O (l)  H 3 O + (aq) + HSO 4 - (aq) HSO 4 - (aq) +H 2 O (l)  H 3 O + (aq) + SO 4 2- (aq) Oxyacids: The acidic hydrogen is attached to an oxygen. Acetic acid is an example CH 3 COOH (aq)

NO 2 (g) + H 2 O  HNO 3 (aq) Nitrogen oxideswaterNitric acid