Exam 3 Flashcards
acids
Donate H+
Molecules - Both organic and inorganic
Cations that contain H
Anions that contain H
Binary acids have acid hydrogens attached to a nonmetal atom.
ex HCl, HF
Oxyacids have acid hydrogens attached to an oxygen atom.
ex H2SO4, HNO3
Carboxylic acids have COOH group. only 1st H in the formula is acidic
ex HC2H3O2, H3C6H5O7
bases
accept H+, usually contain OH-
Ionic compounds that contain OH-
Molecules - Primarily amines
Anions – With and without H
Cations – Few examples
Definitions of Acids and Bases:
Arrhenius, Bronsted-Lowry, Lewis
Brønsted–Lowry definition: Based on reactions in which H+ is transferred
Lewis definition
Arrhenius Theory
Based on H+ and OH-
Acids: produce H+ ions in aqueous solution.
ex HCl(aq) → H+(aq) + Cl−(aq)
Bases: produce OH− ions in aqueous solution.
ex NaOH(aq) → Na+(aq) + OH(aq)
The H+ from the acid combines with the OH− from the base to make a molecule of H2O.
It is often helpful to think of H2O as H—OH.
The cation from the base combines with the anion from the acid to make a salt.
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Problems with Arrhenius Theory
It does not explain why molecular substances, such as NH3, dissolve in water to form basic solutions, even though they do not contain OH– ions.
It does not explain how some ionic compounds, such as Na2CO3 or Na2O, dissolve in water to form basic solutions, even though they do not contain OH– ions.
It does not explain why molecular substances, such as CO2, dissolve in water to form acidic solutions, even though they do not contain H+ ions.
It does not explain acid–base reactions that take place outside aqueous solution.
Hydronium ion
H3O+
The H+ ions produced by the acid are so reactive they cannot exist in water.
H+ ions are protons!
Instead, they react with water molecules to produce complex ions, mainly hydronium ion, H3O+.
H+ + H2O H3O+
Bronsted/Lowry Definition of acid and base
Brønsted-Lowry Acid – A compound that donates a proton to another compound. H+
Brønsted-Lowry Base – A compound that accepts a proton from another compound.
It defines acids and bases based on what happens in a reaction.
Any reaction involving H+ (proton) that transfers from one molecule to another is an acid–base reaction, regardless of whether it occurs in aqueous solution or if there is OH− present.
binary acid
acid hydrogens attached to nonmetal atom
HCl, HBr, HI, HF
HF is weak acid, others strong
ocyacids
acid hydrogens attached to an oxygen atom
H2SO4, HNO3
higher the #oxygens (oxidation number) the stronger the acid
H2SO4 > H2SO3; HNO3 > HNO2
Carboxylic acids
have a COOH group
Only the 1st acid in the formula is acidic
ex HC2H3O2, H3C6H5O7
STRONG Acids
Ka>1;
[H30+]>[OH-]
dissociates (ionizes) completely
donate practically all their H’s.
100% ionized in water
a strong electrolyte
[H3O+] = [strong acid]
yield nearly 100% H30+
Common Strong Acids
HCl, HBr, HI, HNO3, H2SO4, HClO4
WEAK Acids
Ka<1;
dissociates (ionizes) partially; only a small percentage of the molecules ionize;much less than 1% ionized in water
weak electrolyte
[H3O+] «_space;[weak acid]
yield much less than 100% H30+
STRONG Bases
Kb>1;
[OH-]>[H30+]
dissociates (ionizes) completely in H20; Practically all the base molecules form OH– ions
a strong electrolyte
[OH-] = [strong base]
Common Strong Bases
LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
weak bases
Kb<1;
dissociates (ionizes) partially
weak electrolyte
only a small percentage of the base molecules form OH- ions, either through dissociation or reaction with water
Conjugate pairs
An acid donates a proton and becomes a conjugate base.
A base accepts a proton and becomes a conjugate acid.
Each reactant and the product it becomes is called a conjugate pair.
In a Brønsted-–Lowry acid–base reaction, the original base becomes an acid in the reverse reaction. the original acid becomes a base in the reverse process.
Bronsted-Lowry Acid
H+ donors.
Any material that has H can potentially be a Brønsted–Lowry acid.
Because of the molecular structure, often one H in the molecule is easier to transfer than others.
When HCl dissolves in water, the HCl is the acid because HCl transfers an H+ to H2O, forming H3O+ ions.
Water acts as base, accepting H+.
Bronsted-Lowry Base
H+ acceptors.
Any material that has atoms with lone pairs can potentially be a Brønsted–Lowry base.
Because of the molecular structure, often one atom in the molecule is more willing to accept H+ transfer than others.
When NH3 dissolves in water, the NH3(aq) is the base because NH3 accepts an H+ from H2O, forming OH–(aq).
Water acts as acid, donating H+.
amphoteric substance
can act as either an acid or a base because they have both transferable H and an atom with lone pair electrons.
ex H20
Kw
ion product of water
product of [H3O+] and [OH-]
Kw= 1.00x10^-14 at 25*C
[H3O+] and [OH-]
[H3O+] and [OH-] are equal in pure water
[H3O+] and [OH-] are inversely related to each other
[H3O+] >1.00x10^-7 ACIDIC
[OH-]>1.00x10^-7 BASIC
[H3O+] = [OH-] NEUTRAL
pH
pH = -log[H3O+]
and [H3O+] = 10^-pH
pHwater = -log[10^-7] = 7
pH < 7 ACIDIC
pH > 7 BASIC
pH = 7 NEUTRAL
pOH
pOH = -log[OH-]
and [OH-] = 10^-pOH
pOHwater = -log[10^-7] = 7
pOH < 7 BASIC
pOH > 7 ACIDIC
pOH = 7 NEUTRAL
pH + pOH =
14
relative ion concentration and pH
pH < 7; ACIDIC;
[H3O+] > [OH-]
pH > 7; BASIC;
[H3O+] < [OH-]
pH = 7; Neutral;
[H3O+] = [OH-]
The farther the equilibrium position lies toward the products, the ____.
stronger the acid or base.
Commonly, acid or base strength is measured by determining the equilibrium constant of a substance’s reaction with water.
HAcid + H2O ⇌ Acid− + H3O+
Base: + H2O ⇌ HBase+ + OH−
The stronger an acid is at donating H,
the weaker the conjugate base is at accepting H.
Higher oxidation number =
stronger oxyacid
H2SO4 > H2SO3; HNO3 > HNO2
Cation stronger acid than
neutral molecule; neutral stronger acid than anion
H3O+ > H2O > OH−; NH4+ > NH3 > NH2−
Trend in base strength opposite
pH
= -log [H3O+]
pOH
= -log [OH-]
pH + pOH
14
Ka (acid ionization constant)
Ka = [H3O+][A-]/[HA]
Ka = 10^-pKa
Ka and Kb are inversely related
pKa
a way of expressing the strength of an acid or base
pKa = -log(Ka)
the stronger the acid the smaller the pKa (larger Ka)
Kb (base ionization constant)
Kb = [OH-][H:B]/[B]
Kb = 10^-pKb
Ka and Kb are inversely related
pKb
a way of expressing the strength of an acid or base
pKb = -log(Kb)
the stronger the base the smaller the pKb (larger Kb)
Salts
ionic compounds (metal and nonmetal)
can be soluble or insoluble in water
soluble salts act as acid, base, or neutral in water
Salts that consist of
1. anions that are the conjugate base of STRONG acids are NEUTRAL in water (pH=7; ex: HCl, KOH, NaNO3)
- anions that are conjugate bases of WEAK acids are BASIC in water (pH>7; ex NaCN, CH3CO2Na, KF)
- cations that are the conjugate acids of WEAK bases are ACIDIC in water (pH<7; ex NH4Cl +H20 -> acidic and H20 is the weak base)
Salts: cations of group I and II metals are always ___
neutral
transition metals have acidic properties
Buffer
resist changes in pH
weak acid and its conjugate base or weak base and its conjugate acid
buffer capacity
amount of acid or base a buffer can neutralize
depends on 1. the relative amounts of acid and base, and 2. the absolute concentrations of acid and base
most effective when acid and base are equal concentrations
[base]:[acid]=1
will be effective when
0.1< [base]:[acid] < 10
Henderson-Hasselbalch equation
pH = pKa + log ([base]/[acid])
pOH = pKb + log ([salt]/[base])
titration curve
plot of pH versus the amount of added titrant
midpoint of the vertical part of the curve is the equivalence point
acid ionization
reaction involving the transfer of a proton from an acid to water, yielding hydronium ions and the conjugate base of the acid
autoionization
reaction between identical species yielding ionic products; for water, this reaction involves transfer of protons to yield hydronium and hydroxide ions
base ionizations
reaction involving the transfer of a proton from water to a base, yielding hydroxide ions and the conjugate acid of the base
diprotic acid
acid containing two ionizable hydrogen atoms per molecule
diuretic base
base capable of accepting two protons
ion-product constant for water (Kw)
equilibrium constant for the auto ionization of water
percent ionization
ratio of the concentration of ionized acid to initial acid concentrations expressed as a percentage
common ion effect
effect on equilibrium when a substance with an ion in common with the dissolved species is added to the solution; causes a decrease in the solubility of an ionic species, or a decrease in the ionization of a weak acid or base (le chattliers)
dissociation constant (Kd)
equilibrium constant for the decomposition of a complex ion into its components
formation constant (Kf)
also stability constant
equilibrium constant for the formation of a complex ion from its components
lewis acid
lewis base
Lewis acid: accepts a pair of elections
Lewis base: donates a pair of electrons
coordinate covalent bond (dative bond)
a type of bond that forms when one of the atoms in the bond provides both bonding electrons
lewis acid base adduct
a compound that contains a coordinate covalent bond formed between a lewis acid and lewis base
