Chapter 8.1 & 8.2: Acids and Bases What are acids: – any compound that increases the number of hydronium ions (H 3 O + ) when dissolved in water. Hydronium forms when hydrogen ions from the compound combine with water molecules You can also think of an acid as making H +. H 3 O +  H 2 O + H +

Acids HNO 3 + H 2 O  H 3 O + + NO 3 -

Acids This process of breaking down in water is called ionization. Acids that completely ionize called strong acids (e.g hydrochloric, HCl). Ones that do not are called weak acids (e.g. citric acid) Movie: Strength of Acids and Bases

What is a base? Any compound that increases the number of hydroxide (OH - ) ions when dissolved in water. They do this through dissociation. NH 3 + H 2 O  NH OH -

Bases There are strong and weak bases, too, based on whether they completely dissociate or not. Strong acids and bases are also strong electrolytes. That means that they conduct electricity, due to the ions they make. Note: Whether an acid or base is strong or weak has nothing to do with its “damage” ability! Concentration is important, too. A strong acid/base can be diluted and not very dangerous.

acid or a base? HClH 2 SO 4 Ca(OH) 2 H 3 PO 4 NaOHLiOH HCO 3 NH 4 OH If it starts with H…it’s usually an acid If it ends in OH…it’s usually a base acid base acid base acid base acidbase

What is pH? It stands for Pouvoir Hydrogene, the power of hydrogen. It’s a measure of the concentration of Hydrogen ions in a solution Usually goes from 0 – 14, 7 = neutral Acids < 7 < Bases The farther away from 7 you get, the more powerful/dangerous the acid or base.

What is pH? pH scale is logarithmic…goes by factor of 10, e.g. 4 is 10 times more acidic than 5 and 100 times more acidic than 6 You can use an indicator (chemical that changes color) to tell whether something is an acid or base. Acids and bases are equally dangerous, depending on their pH. Something with a pH of 1 will hurt you just as much as 14! Movie: pH

What is pH?

Acid-base Reactions When an acid and base are mixed together, it is called a neutralization reaction. It forms water (from H + and OH - ) and a salt (from the other ions). Movie: Neutralization reaction

What salt would form from HCl + NaOH H 2 SO 4 + Ca(OH) 2 HBr + Ca(OH) 2 H 3 PO 4 + Al(OH) 3 HF + Al(OH) 3 H 2 SO 4 + NaOH HNO 3 + NH 4 OH NaCl CaSO 4 CaBr 2 AlPO 4 AlF 3 Na 2 SO 4 NH 4 NO 3 Once the H and OH are gone, whatever is left makes the salt. But the charges still have to balance.

Acid-base Reactions You can add one to the other in the presence of an indicator to tell when it is neutralized. This is called a titration. The pH where it is neutralized is called the equivalence point. The equivalence point is not always pH 7, e.g. weak acid + strong base…pH > 7 (basic)

If you graph a titration… At what concentration of KOH is the equivalence point? How can you tell? This would also tell you the original concentration of acid. Note how quickly the pH changes from about 4 to 10!