Sec 14.2 Brownsted-lowry
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Bronsted-Lowry Acids and Bases Sec 14-2
Bronsted-Lowry Acids & Bases
Bronsted-Lowry Acid: is a molecule or ion that is a proton donor.
Ex)
Water can also act as a Bronsted-Lowry Acid
ex)
HCl + NH3 NH4+ + ClHCl + H2O H3O+ + Cl-
H2O + NH3 NH4+ + OH-
Bronsted-Lowry Acids & Bases
Bronsted-Lowry Bases: are molecules or ions that are a proton acceptor.
HCl + NH3 NH4+ + Cl- (NH3 is base)
In Bronsted-Lowry acid-base reactions, protons are transferred from one reactant (the acid) to another (the base)
Monoprotic & Polyprotic Acids
Monoprotic acid is an acid that can donate only one proton per molecule.
ex) HClO4, HCl, HNO3
Polyprotic acid is an acid that can donate more than one proton per molecule
Ex) H2SO4, H3PO4
Ionization of polyprotic acids occurs in stages.
The acid loses its hydrogen atoms one at a time.
Polyprotic Acids Can vary in the number of protons they donate Diprotic acid can donate 2 protons per molecule
Ex) H2SO4
Triprotic acid can donate 3 protons per molecule
Ex) H3PO4
Ionization of Polyprotic Acids All stages of ionization of polyprotic acids occur in the same solution Ex) H2SO4 + H2O H3O+ + HSO4
HSO4- + H2O ↔ H3O+ + SO4The solution contains all three ion, H3O+ , HSO4-, & SO4-
Ionization of Polyprotic Acids
With most polyprotic acids, the concentration of ions formed in the first ionization is the greatest.
Conjugate Acids & Bases
Conjugate base is the species that remains after a Bronsted-Lowry acid has given up a proton.
Conjugate Acids & Bases
Conjugate Acid the species that is formed when a Bronsted-Lowry base gains a proton.
In general, Bronsted-Lowry reactions are equilibrium rxn’s, that occur in both directions. They involve 2 acid-base pairs known as conjugate acid base pairs.
Strength of Conjugate Acids and Bases The extent of a rxn between a BronstedLowry acid and base depends on the relative strengths of the acids and bases involved. Ex) HCl + H2O H3O+ + Cl
strong base acid weak acid base The stronger an acid is, the weaker its conjugate base; the stronger a base is, the weaker its conjugate acid.
Strength of Conjugate Acids and Bases
Hydronium is too weak an acid to compete with perchloric acid in donating a proton
Both ClO4- and H2O are bases
HClO4 is the stronger acid Since HClO4 is a very strong acid ClO4- is a very weak base and water, the stronger base, acquires more of the protons
The rxn proceeds such that the stronger acid reacts with the stronger base to produce the weaker acid and base
Strength of Conjugate Acids and Bases
Proton transfer reactions favor the production of the weaker acid and the weaker base.
Amphoteric Compounds
Any species that can react as either an acid or a base
How they react depends on the strength of the acid or base they are with.
-OH in a Molecules Molecular compounds contains the –OH group can be acid or amphoteric To be acid
Water must be able to attract H+ from OH Occurs more easily if O-H bond is very polar Any feature that increases the polarity of the O-H bond increases the substances acidity.
Ex) be bonded to more electronegative non-metals Ex) Increasing the number of oxygen atoms bonded to the same atom as the OH (hydroxyl group)
Bronsted-Lowry Acids & Bases
Bronsted-Lowry Acid: is a molecule or ion that is a proton donor.
Ex)
Water can also act as a Bronsted-Lowry Acid
ex)
HCl + NH3 NH4+ + ClHCl + H2O H3O+ + Cl-
H2O + NH3 NH4+ + OH-
Bronsted-Lowry Acids & Bases
Bronsted-Lowry Bases: are molecules or ions that are a proton acceptor.
HCl + NH3 NH4+ + Cl- (NH3 is base)
In Bronsted-Lowry acid-base reactions, protons are transferred from one reactant (the acid) to another (the base)
Monoprotic & Polyprotic Acids
Monoprotic acid is an acid that can donate only one proton per molecule.
ex) HClO4, HCl, HNO3
Polyprotic acid is an acid that can donate more than one proton per molecule
Ex) H2SO4, H3PO4
Ionization of polyprotic acids occurs in stages.
The acid loses its hydrogen atoms one at a time.
Polyprotic Acids Can vary in the number of protons they donate Diprotic acid can donate 2 protons per molecule
Ex) H2SO4
Triprotic acid can donate 3 protons per molecule
Ex) H3PO4
Ionization of Polyprotic Acids All stages of ionization of polyprotic acids occur in the same solution Ex) H2SO4 + H2O H3O+ + HSO4
HSO4- + H2O ↔ H3O+ + SO4The solution contains all three ion, H3O+ , HSO4-, & SO4-
Ionization of Polyprotic Acids
With most polyprotic acids, the concentration of ions formed in the first ionization is the greatest.
Conjugate Acids & Bases
Conjugate base is the species that remains after a Bronsted-Lowry acid has given up a proton.
Conjugate Acids & Bases
Conjugate Acid the species that is formed when a Bronsted-Lowry base gains a proton.
In general, Bronsted-Lowry reactions are equilibrium rxn’s, that occur in both directions. They involve 2 acid-base pairs known as conjugate acid base pairs.
Strength of Conjugate Acids and Bases The extent of a rxn between a BronstedLowry acid and base depends on the relative strengths of the acids and bases involved. Ex) HCl + H2O H3O+ + Cl
strong base acid weak acid base The stronger an acid is, the weaker its conjugate base; the stronger a base is, the weaker its conjugate acid.
Strength of Conjugate Acids and Bases
Hydronium is too weak an acid to compete with perchloric acid in donating a proton
Both ClO4- and H2O are bases
HClO4 is the stronger acid Since HClO4 is a very strong acid ClO4- is a very weak base and water, the stronger base, acquires more of the protons
The rxn proceeds such that the stronger acid reacts with the stronger base to produce the weaker acid and base
Strength of Conjugate Acids and Bases
Proton transfer reactions favor the production of the weaker acid and the weaker base.
Amphoteric Compounds
Any species that can react as either an acid or a base
How they react depends on the strength of the acid or base they are with.
-OH in a Molecules Molecular compounds contains the –OH group can be acid or amphoteric To be acid
Water must be able to attract H+ from OH Occurs more easily if O-H bond is very polar Any feature that increases the polarity of the O-H bond increases the substances acidity.
Ex) be bonded to more electronegative non-metals Ex) Increasing the number of oxygen atoms bonded to the same atom as the OH (hydroxyl group)
