definition of acids traditional (arrhenius)- a chemical compound that contains hydrogen and...

Definition of Acids

• Traditional (Arrhenius)- a chemical compound that contains hydrogen and ionizes in aqueous solutions to form hydrogen ions

Examples:HNO3 + H2O H3O+ + NO3

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Bronsted-Lowry Acids• expanded the Arrhenius definition by saying an

acid is a molecule or ion that is a proton (H+) donor

So…Arrhenius acids donate protons to water but other substances can also donate protons

Even water can act as a Bronsted-Lowry AcidH2O + NH3 NH4

+ + OH-

Lewis Acids

• Allows substances that do not contain hydrogen to be considered acids

• A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond

Example- Boron trifluorideBF3 + F- BF4

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Properties of Acids

• Sour taste• Produce predictable color changes in the

presence of an indicator• React with bases to produce salt and

water• Electrolytes• Some react with active metals releasing

hydrogen gas

Strong vs. Weak Acids

• A strong acid ionizes completely in solution and as a result is a strong electrolyte

Examples: HBr, HCl see p. 474• Weak acids do not ionize completely in

solution and are weak electrolytes.Examples: HF, HCN see p. 474

Common Acids and Uses

• Sulfuric Acid- battery acid, dehydrating agent

• Nitric Acid- explosives• Hydrochloric Acid- common lab acid,

pickling• Acetic Acid- vinegar

Definition of Bases

• Traditional- a substance that contains hydroxide ions (OH-) and dissociates to give hydroxide ions in aqueous solutions

• Examples:NaOH Na+ + OH-

NH3 + H2O NH4+ + OH-

• Bronsted-Lowry base- a molecule or ion that is a proton acceptor

• Lewis base- an atom, ion, or molecule that donates an electron pair to form a covalent bond

Properties of Bases

• Bitter taste• Feel slippery• Produce predictable color changes in the

presence of an indicator• React with acids to produce salt and water• Electrolytes

Strong vs. Weak Bases

• Strong bases dissociate completely in solution

KOH K+ + OH-

• Weak bases do not dissociate completelyNH3 + H2O NH4

+ + OH-

pH Scale

• Ranges from 0 to 14• Values from 0 to 6.9 are acidic• Values from 7.1 to 14 are basic• A value of 7 is neutralMeasuring pH1. Indicators2. pH meters3. pH paper

Neutralization Reactions

• The reaction of hydronium ions (H3O+) and hydroxide ions (OH-) to form water molecules

• The products of a neutralization reaction are neither acidic or basic but are neutral

Example:HCl + NaOH NaCl + H2O

• Na+ and Cl- are only spectator ions (an ion that does not take part in a reaction and is found in solution both before and after the reaction)

• The reaction occurs between the hydronium ion (H3O+) and the hydroxide ion (OH-)

Net ionic eq. (H3O+ + OH- 2H2O)

Salts

• Are formed from a neutralization reaction• Are ionic compounds composed of a metal

cation of an aqueous base and the anion from an aqueous acid

Example:H2SO4 + 2NaOH Na2SO4 + 2H2O

(acid) (base) (salt)

Principles of Titration• A titration is the operation of gradually adding

one solution to another to reach an equivalence point ( the point at which a neutralization reaction is complete)

• Titrant- the solution added to another solution in a titration

• Standard solution- one whose concentration is accurately known

• End point- the point at which an indicator changes color

Read p.515-521

Conjugate Acids/Bases• Conjugate base- the species that remains

after a Bronsted-Lowry acid has given up a proton

Example: HF + H2O F- + H3O+

acid conjugate base

Conjugate acid- the species that is formed when a Bronsted-Lowry base gains a proton

• Example: HF + H2O F- + H3O+

base conjugate acid

Calculation of H3O+ and OH- Concentration

• Water will self-ionize to form hydronium and hydroxide ions in solution

H2O + H2O H3O+ + OH-

• Measurements show that the conc. of both

the hydronium ion and hydroxide ion in pure water are both equal to 1.0 x 10-7 M. Because their conc. are the same, pure water is a neutral

Ionization Constant of Water

• Kw = [H3O+][OH-] = 1.0 x 10-14

Strong acids and bases completely ionize or dissociate to form H3O+ and OH- in solution so….

Conc. of a strong base = [OH-]Conc. of a strong acid = [H3O+]

Example Problems

• A 1.0 x 10-4 M solution of HNO3 has been prepared. Calculate the hydronium ion conc. and the hydroxide ion conc.

• Determine the hydronium ion and hydroxide ion conc. in a solution that is

3.0 x 10-2 M NaOH.

Calculating pH

• pH = -log[H3O+]Examples:1. What is the pH of a 1.0 x 10-3 M NaOH

solution?2. What is the pH of a 1.0 x 10-5 M HNO3

solution?

Calculating [H3O+] and [OH-] from pH

• [H3O+] = 10-pH

Examples:1. The pH of a solution is 7.52.a. What is the hydronium ion conc.?b. What is the hydroxide ion conc.?c. Is the solution acidic or basic?