definition of acids traditional (arrhenius)- a chemical compound that contains hydrogen and...
DESCRIPTION
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 Acid H 2 O + NH 3 NH OH - TRANSCRIPT
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
-
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
-
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?