Chemical Equilibria and Neutralization
Which of the following are weak bases? (Select all that apply) -KOH -HCl -(C2H5)2NH -NH3 -HNO2
(C2H5)2NH NH3
Which of the following are strong bases? -Fe(OH)3 -Al(OH)3 -Ca(OH)2 -KOH -Ba(OH)2 -NaOH
-Ca(OH)2 -KOH -Ba(OH)2 -NaOH
Strong Acids
-acids for which the equilibrium constant for dissociations is so large that we assume the molecules "fall apart" or dissociate 100% in water [H3O+]≈CHA HCl, HBr, HI, HClO4, HClO3, H2SO4, HNO3
Lowry-Bronsted Definition of Acids and Bases
-an acid is a proton donor -a base is a proton acceptor
Lewis Definition
-an acid is an electron pair acceptor -a base is an electron pair donor
pH
-expresses Hydronium ion concentration in an aqueous solution using log base 10 pure water at 25°C has a pH of 7 pH = -log[H3O+ [H3O+]= 10 ^(-pH)
When comparing two 1M solutions of different weak acids, the acid solution with the larger Ka value will ________.
-have a smaller Kb value -ionize to a greater extent
Le Chatelier's Principle
-how a reaction mixture that is at equilibrium will react when it is perturbed away from equilibrium -if a chemical system at equilibrium experiences a change, then the equilibrium shifts to counteract the imposed change and a. new equilibrium is established -Changes that cause the system to move away from equilibrium: adding/removing reactant or product, changing the volume (pressure) for a reaction with gases, changing the temperature
Le Chatelier and Volume
-only possible for reaction involving gas -decreasing volume increases pressure; increasing volume decreases pressure -volume only affects reactions that have different numbers of moles of gas in the products and reactants
Which of the following are strong acids? -perhchloric acid -hydroflouric acid -chloric acid -nitric acid -hydrobromic acid -nitrous acid
-perchloric acid -chloric acid -nitric acid -hydrobromic acid
weak acids
-proton donor that only partially dissociates Ka = [products]/[reactants] [H3O+]=sqrt((Ka)(CHA))
mass action expression
-the current set of activities of the reactants and products put into an equation that maps a generalized numeric scale -a ratio of the activities of the products and he reactants aA + bB -> cC + dD [C]^c [D]^d / [A]^a [B]^b
activities
-track amounts of substances whether they are solids, liquids, or gases or aqueous species -unitless number that is a function of the concentration or pressure of the substance as it is referenced to a standard state -tell us how the free energy varies with progress of the reaction
The Kb of methylamine is 4.4 x 10-4. What is the approximate [OH-] of a 1M solution of methylamine?
0.021 M
What do the question marks in the table below represent? R. A + 2B ⇌ C I. 0.1 M 0.8 M 0 M C -x -2x. +x E. ?? 0.8M-2x x
0.1 M - x
What is the percent ionization of a 2M solution of acetic acid at 25˚C?
0.3%
Calculate the resulting pH if 365 mL of 2.88 M HNO3 is mixed with 335 mL of 1.10 M Ca(OH)2 solution. Be aware of stoichiometry!
0.35
Fill in the blanks in the table below. R. 2A + 2B ⇌ C + D I. 3.5 M. ______. 0M. 0.1 M C. -2x. -2x. +x. _____ E ______. 0.9M-2x x. 0.1M + x
0.9 M ; +x ; 3.5M - 2x
What is the pH of a 0.12 M solution of HNO3?
0.92
You have a 1M solution of formic acid. In that solution the approximate concentration of protonated formic acid is
1 M since it is a weak acid and only a very small fraction dissociates
Acid/Base Chemistry
1. You put stuff in water and something happens; water solvates chemical species and allows them to break apart into ions 2. an acid is a proton donor and a base is a proton acceptor 3. acids/bases that break apart completely are strong, acids/bases that only partially break apart are weak Acid/Base Compounds can be found in one of two forms: 1. The protonated form: the proton is on the molecule (acid) 2. the de-protonated form: the proton is off the molecule (Base)
Two equilibria to think about
1. the equilibrium of the acid (or base) with the water 2. the equilibrium of water itself with H3O+ and OH-
Please consider the following reaction: NO (g) + (1/2)O2 (g) ⇌ NO2 (g) At 298K, ∆H˚rxn = -56.52 kJ mol-1 and ∆S˚rxn = -72.6 J K-1 mol-1. What is the value of the equilibrium constant for this reaction at 298K?
1.3E6
What is the equilibrium concentration of substance A given that Kc = 4.0 x 10-2? Here is the reaction: 2A ⇌ B + C The initial concentration of A is 1.7 M, the initial concentration of B is 0.2 M and the initial concentration of C is 0.2 M.
1.5 M
If the equilibrium constant for this reaction N2 (g) + 3H2 (g) ⇌ 2NH3 (g) is K, what is the equilibrium constant for the following reaction? NH3 (g) ⇌ (1/2)N2 (g) + (3/2)H2 (g)
1/sqrtK
For a solution in which the pH is 2 at 25˚C what are the values for [H3O+], [OH-] , and pOH respectively?
10-2 M, 10-12 M, 12
In a solution that has a pH of 10, the hydronium ion concentration is _______ than a solution with a pH of 13.
1000 times larger
What is the pH of a 0.1 M solution of NaOH?
13
Kw
1E-14 Kw= Ka x Kb
At 25°C, you have an aqueous solution for which [H3O+] = 1 x 10-5 M. What is the [OH-]?
1E-9 M
The Ka of benzoic acid is 6.4 x 10-5. What is the approximate pH of a 1.5 M solution of benzoic acid?
2
You have a solution for which the hydronium ion concentration is 4.5 x 10-4 M. What is the concentration the hydroxide ion, OH- in this solution at 25°C?
2.22 x 10-11
You have an aqueous solution for which [H3O+] = 2.5 x 10-4 M. What is the pH of this solution?
3.6
Ammonia, NH3, is a weak base with a Kb = 1.8 x 10-5. In a 0.8M solution of ammonia, what is the concentration of the ammonium ion, NH4+?
3.8 x 10-3 M
Dimethylamine, (CH3)2NH, has a Kb value of 5.4 x 10-4. In a 1.2 M solution of dimethylamine at 25˚C what is the concentration of H3O+?
4.0 x 10-13 M
At a particular temperature you find the following reaction at equilibrium with the given concentrations of gases: 4HCl (g) + O2 (g) ⇌ 2H2O (g) + 2Cl2 (g) [HCl] = 0.1 M ; [O2] = 0.1 M ; [H2O] = 2 M ; [Cl2] = 0.1 M What is the value of Kc at this temperature?
4000
At 25°C, you have an aqueous solution for which [H3O+] = 1.0 x 10-9 M. What is the pOH of the solution?
5
Benzoic acid, C6H5COOH, has a Ka = 6.4 x 10-5. What is the concentration of H3O+ in a 0.5 M solution of benzoic acid?
5.6 x 10-3 M
Which of the following are the weak base conjugates of weak acids? (Select all that apply) CH3NH3+ CH3COO- Ba(OH)2 CN- HNO3 F- NO2-
CH3COO- CN- NO2- F-
According to the Lowry-Bronsted Theory, what is the conjugate base of HCN?
CN-
In acid/base chemistry, which of the following ions would be considered "spectator ions"? (select all that apply) Ca2+ CN- K+ I- NH4+ ClO4- F-
Ca2+ K+ I- ClO4-
which of the following is an acidic salt?
Ch3NH3NO3
In all acid/base chemistry we are often tracking a small concentration of two ions in water. These are, water with an extra proton, ______, called _____ ion. Or water minus a proton, _______, called the _______ ion. Note: often chemists are lazy and simply interchange H3O+ and _____ in aqueous solution.
H3O+, hydronium OH-, hydroxide, H+
What acid and what base would you choose to prepare the salt potassium perchlorate KClO4?
HClO4 and KOH
Which of the following are weak acids? (Select all that apply) -HCl -HF -HCN -NaOH -NH3
HF HCN
According the the Lowry-Brønsted theory, the conjugate base of H2SO4 is
HSO4-
equilibrium constant
K = (conc of products raised to their coefficients) / (conc of reactants raised to their coefficients) -if K > 1, "more products" at equilibrium -if K < 1 "more reactants"
Write the equilibrium constant expression given the following partially filled out RICE table: R. A ⇌ 2B + C I. 0.8 M 0 M 0.2 M C. - x E.
K= (2x)^2 (0.2M +x) / (0.8M -x)
Which of the following are weak bases in water? KF CH3COOH Ba(OH)2 NH4Cl HI NaCH3COO NH3
KF NaCH3COO NH3
Consider the following generic weak acid, HA, that dissociates in water according to this equation: HA (aq) + H2O (l) ⇌ A- (aq) + H3O+ (aq) The Ka for this acid is 8.33 x 10-2. You are given a solution of 1M HA and you are told that x = 0.25 M. What is the best way to set up your Ka expression to verify this value for x?
Ka = (x*x)/(1-x)
Kp & Kc
Kp=Kc(RT)^Δn
Given a generic base, B, and its Kb value, which of the following expressions would you use to solve for the Ka of the conjugate acid, BH+?
Kw/Kb
Match the different categories of acids and bases with their descriptions: Lowry-Bronsted Base Lowry-Bronsted Acid Lewis base Lewis Acid Arrhenius Base Arrhenius Acid
LB Base: proton acceptor LB Acid: proton donor Lewis base: electron pair donor Lewis acid: electron pair acceptor Arrhenius Base: Increases the OH- conc Arrhenius Acid: increases the H+ conc
In this reaction CH3NH2 (aq) + H2O (l) ⇌ CH3NH3+ (aq) + OH- (aq) CH3NH2 acts as a
Lowry-Bronsted Base
which salt is not derived from a strong acid and a strong soluble base
MgCl2
Ammonia, NH3, is a weak base with a Kb = 1.8 x 10-5. In a 0.8M solution of ammonia, which has a higher concentration: ammonia (NH3) or its conjugate acid the ammonium ion (NH4+)?
NH3
Which of the following are the weak acid conjugates of weak bases? (Select all that apply) F- NH4+ CH3COO- C3H8COOH C6H5NH2
NH4+ C3H8COOH
Mass expression using pressures
P(c)P(d) / P(a)P(b)
Reaction Quotient (Q)
Q = ([C]^c [D]^d)/([A]^a [B]^b) -current "now" free energy of the system
RICE tables
R: the top line is the reaction I: the next line is initial conditions of conc or pressure C: the third line is the amount that reacts(change line) E: actual equilibrium amounts
What is the correct mass action expression in terms of concentrations for the equilibrium constant of the given reaction: 3Cu (s) + 2NO3- (aq) + 8H+ (aq) ⇌ 3Cu2+ (aq) + 2NO (g) + 4H2O (l)
[Cu2+]^3[NO]^2 / [No-3]^2 [H+]^8
Basic
[H3O+] < [OH-]
A solution is neutral when __________.
[H3O+] = [OH-].
neutral
[H3O+] = [OH] = 1x10-7 M.
Acidic
[H3O+] > [OH-]
What will happen if I add a substance that dissociates to provide many hydroxide ions, such as a strong base, into pure water? (Select all that apply)
[H3O+] decreases the equilibrium of water auto ionization shifts to the reactant side [OH-] increases
What is true about a solution of 1 M HCl? (select the best answer)
[H3O+] ≈ 1 M
Consider a solution of 0.035 M Ca(OH)2 at 25˚C.
[OH-] ≈ 0.07 M [H3O+] ≈ 1.4 x 10-13 M Kw = 1 x 10-14 the solution is basic
activities of pure solid and liquids
a(i) = 1
activities of gases
a(i) = P(i)/P° (P° is the standard pressure of 1 atm)
activities of solutions
a(i) = [i]/C° (Standard concentration C° is 1 M)
If you mix 100 mL of 0.1 M NH3 with 50 mL of 0.2 M HCl, the resulting solution will be ___________. Consider how the products (the salt and the water) of this reaction might interact.
acidic
For the following reaction at equilibrium, which applied stresses will cause the reaction to shift to form more products as it re-equilibrates N2 (g) + 3H2 (g) ⇌ 2NH3 (g) Check all that will shift the reaction toward the products
adding hydrogen gas, adding nitrogen gas, removing ammonia gas
Salts
an acid and a base react to form a sale
Arrhenius definition
an acid produces H3O+ ions in water a base produces OH- ions in water
At 25°C, you find that a solution has a hydronium ion concentration of 1.2 x 10-11 M. This solution would be considered:
basic
Le Chatelier's Principle states: If a chemical system at equilibrium experiences a(n) ________ , then the equilibrium ________ to counteract the imposed change and a new ___________ is established.
change; shifts; equilibrium
For the following reaction is exothermic. Which applied stresses (if any) will cause the reaction to shift to form more products as it re-equilibrates? N2 (g) + 3H2 (g) ⇌ 2NH3 (g) Check all that will shift the reaction toward the products:
decreasing the volume, decreasing the temperature
Strong Bases
dissociate 100% in water [OH−]≈CB LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
Consider a sample of pure liquid water. Since the dissociation of water is _____, as we increase the temperature the equilibrium constant will ______. Thus at higher temperature the concentration of both the hydronium ion and hydroxide ion will increase. They will no longer be 1x10-7 M; they will be slightly larger. However, the solution will still be _________. This is because [H3O+] is _______ [OH-].
endothermic; increase; neutral; equal to
Le Chatelier and Temperature
exothermic: reactants⇌products+heat endothermic: reactant+heat⇌products K=exp(−ΔH∘rRT)×constant
true or false? at equilibrium, the reaction has stopped
false
Here is a list of three acids with their Ka values and three bases with their Kb values. Acids: hydrofluoric acid (HF) Ka = 6.3 x 10-4 ammonium (NH4+) Ka = 1.35 x 10-10 hypochlorous acid (HOCl) Ka = 3.5 x 10-8 Bases: hydroxylamine (NH2OH) Kb = 1.1 x 10-8 ammonia (NH3) Kb= 1.8 x 10-5 hydrazine (NH2NH2) Kb = 1.7 x 10-6 The strongest acid is _________ . The strongest base is ________.
hydrofluoric acid; ammonia
neutralization
if a strong base and strong acid are combined, a neutral salt is formed
Use your knowledge of Le Chatelier's Principle to answer the following question: Which of the following (if any) will lead to a change in the equilibrium constant for the following reaction: 2NO2 (g) ⇌ N2O4 (g) Check all that apply
increasing the temperature
Van't Hoff Equation
ln(K2/K1)=ΔHR(1/T1−1/T2) relates two K values to two temperatures
A _______ reaction is the reaction of an acid and a base. After mixing an acid and a base the solution cannot have high concentrations of both H3O+ and any ________. After mixing an acid and a base the solution cannot have high concentrations of both OH- and any ________.
neutralization; base; acid
You find the following reaction at equilibrium. What will happen if you remove some of the solid AgCl? Ag+ (aq) + Cl- (aq) ⇌ AgCl (s) Check all the apply
nothing
pOH
pOH = -log[OH-] pOH = 14- pH [OH-] = 10^(-pOH)
percent ionized
percentionized = [F−]/CHF×100%
When the value of K is a number much greater than 1, we say that the reaction favors the _____.
products
weak bases
proton acceptors that partially dissociate Kb = [products]/[reactants] [OH-] = sqrt((Kb)(CB))
Claussius- Clapeyron Equation
relates two vapor pressures at two volumes ln(P2/P1)=ΔHR(1/T1−1/T2)
Identify the salt that is produced from the acid-base neutralization reaction between sodium hydroxide and hydrocyanic acid (HCN).
sodium cyanide
If \Delta G_{\rm{rxn}}^{\circ}ΔG∘rxn is negative then we say that the forward reaction is ______ and that K is ______. Such a reaction favors the ________.
spontaneous; greater than 1; products
Ka for formic acid is 1.8 x 10-4 Ka for benzoic acid is 6.4 x 10-5 based on this, which is the stronger BASE?
the benzoate anion
You find the following reaction at equilibrium in a container with a total pressure of 10 atm, and a constant volume and temperature. 2SO2 (g) + O2 (g) ⇌ 2SO3 (g) You add to this mixture sufficient non-reactive helium gas such that the final pressure is now 20 atm while the volume and temperature remain unchanged. This has no effect on the equilibrium. Why?
the partial pressure of the gases remain unchanged
when fully calculated the mass action expression will equal this term no matter what conditions are present
the reaction quotient, Q
Recalling all that you know about ∆Gr, K and Q please consider the following situation. The value of Kc for the reaction below is 46 at a particular temperature. H2 (g) + I2 (g) ⇌ 2HI (g) You have a mixture at this temperature that has the following concentrations: [H2] = 0.1 M, [I2] = 1 M, [HI] = 4 M which of the following statements is true:
the reaction will form more reactants as it proceeds towards equilibrium
You have the following reaction drug (aq) + protein (aq) ⇌ complex (aq) describing a drug binding to the active site in a protein. If this reaction is at equilibrium, what is the effect (if any) of diluting the entire mixture by adding more liquid water?
the reaction will shift to the left
what are the units for activity?
there are no units, activities are unitless
The equilibrium constant for dissociations of strong acids and bases are _______ which is why these dissociations essentially go to _______.
very large; 100% completion
For all conjugate pairs, the stronger the acid, the ______ the base; the stronger the base, the ______ the acid.
weaker; weaker
What is the correct mass action expression for the equilibrium constant for this reaction written in terms of partial pressures: N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
{{P_{NH_3}^2 / P_{N_2}P_{H_2}^3}}
change in free energy
ΔGr=ΔG∘r+RTlnQ -instantaneous difference in free energy btw reactants and products at any given set of concentrations -depends on standard free energy difference -if ΔG∘r is negative, the products are lower in free energy and if its positive the reactants are lower - the more negative, the closer to the products -the more positive, the closer to the reactants -Q<K reactants favored, moves forward -Q>K products favored, reaction goes in reverse K=exp(−ΔG∘rRT) -lowest point on graph is equilibrium
