chapter 8.1 & 8.2: acids and bases

Chapter 8.1 & 8.2: Acids and Bases

• What are acids:– any compound that increases the number

of hydronium ions (H3O+) 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+.

• H3O+ H2O + H+

Acids

HNO3 + H2O H3O+ + NO3-

The H+ from HNO3 goes onto H2O and becomes H3O+. That’s why its and acid.

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.NH3 + H2O NH4

+ + 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?• HCl H2SO4

• Ca(OH)2 H3PO4

• NaOH LiOH• HCO3 NH4OH• If it starts with H…it’s usually an acid• If it ends in OH…it’s usually a base

acidbase

acid

baseacidbase

acid base

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• Can be higher than 14 or lower than 0, but

that’s unusual• 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• H2SO4 + Ca(OH)2

• HBr + Ca(OH)2

• H3PO4 + Al(OH)3

• HF + Al(OH)3

• H2SO4 + NaOH• HNO3 + NH4OH

NaClCaSO4

CaBr2AlPO4

AlF3

Na2SO4

NH4NO3• 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!