General Chemistry II: Chapter 16. Acids and Bases
Which is the correct equation for the calculation of percent ionization of the weak acid HA in aqueous solution?
% ionization = [H⁺]eq / [HA₀] x 100
Which of the following statements accurately describe the characteristics of polyprotic acids? Select all that apply.
-A polyprotic acid has more than one ionizable proton. -Polyprotic acids are generally weak acids.
Which of the following solutions of HCN will have the greatest percent ionization? 0.010 M 0.0010 M 0.00010 M 0.10 M
0.00010 M
Which of the following can NOT be used as an acid-base buffer? Select all that apply.
0.5 M HNO₃ and 0.5 M NaNO₃ 0.3 M HCl and 0.3 M NaOH
Rank the sequence of the steps you would use to calculate Kb starting with the pH of a weak base solution of known initial concentration.
1) Use pH to calculate pOH. 2)Calculate [OH⁻] from pOH. 3) Use [OH⁻] and reaction stoichiometry to calculate equilibrium concentrations of HB⁺ and B. 4) Use the equilibrium expression and calculate the value of Kb.
Correctly order the steps necessary to solve weak-acid equilibrium problems, starting with the first step at the top of the list.
1) Write the balanced equation and Ka expression. 2) Define x as the unknown change in concentration that occurs in the reaction and assume x is small compared to [HA]. 3) Construct a reaction table that incorporates x, and solve for x by substituting values into the Ka expression. 4) Check that assumptions are justified, using 5% test. If not justified , use the quadratic formula to find x.
Place the following pH values in order of increasing [H₂O⁺]. Start with the pH that corresponds to the lowest [H₃O⁺] at the top of the list.
1) pH = 8.5 2) pH = 7.2 3) pH = 4.3
Which of the following options correctly describe behavior of strong and weak acids (general formula HA) in aqueous solution? Select all that apply.
A weak acid is a weak electrolyte The solution of a strong acid will have a negligible concentration of unionized HA molecules.
What is the predominant factor in determining the acid strength of binary hydrohalic acids?
Bond enthalpy
Arrange the following acids in order of greatest (at the top of the list ) to least (at the bottom of the list) amount of H₃O⁺ produced in solution at a given concentration.
HCIO₂ (Ka = 1.1 x 10⁻²) HF (Ka = 6.8 x 10⁻4) HCIO (Ka = 2.9 x 10⁻⁸) HCN (Ka = 6.2 x 10⁻¹⁰)
Arrange the following compounds in order of increasing acid strength (weakest at the top to strongest at the bottom of the list)
HF HBr HI
With reference to the table provided, compare the relative strengths of the acids and bases involved in the reaction shown, and predict the preferred direction of reation. HCOOH (aq) + F (aq) ⇌ HCOO (aq) + HF (aq)
HF is a stronger acid than HCOOH. The reaction favors the reactants
Which of the following types of substances are classified as acids only under the Lewis definition? Select all that apply.
Molecules that contain a polar multiple bond. Molecules with electron deficient central atoms.
Select the statement that correctly explains why it is reasonable to assume that for a week acid [HA] at equilibrium is approximately equal to [HA]init under most circumstances.
Most molecules of the weak acid remain unionized at equilibrium.
Which of the following species are weak acids? Select all that apply. HBr H₂SO₄ NH4⁺ HF HNO₂
NH₄ HF HNO₂
Select all the options that correctly account for the behavior of NH₄Cl in aqueous solution.
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺ The solution will have a pH< 7.00
What is the conjugate base of HNO₂ if it reacts as Bronsted acid in H₂O?
NO₂⁻
Select all the reactions in which the Lewis acid is a cation and the Lewis base is a molecule with one or more lone pairs of electrons.
Ni²⁺ + 6NH₃ ⇌ Ni(NH₃)₆²⁺ Fe³⁺ = 6H₂O ⇌ Fe(H₂O)₆ ³⁺
Calculate [OH⁻] in a solution that has [H₃O⁺] = 6.7 x 10⁻² M. is the solution acidic or basic?
The solution is acidic 1.5 x 10⁻¹³ M
Which of the following statements correctly describe the relationship between a weak acid or base and its conjugate base or acid? Select all that apply.
The stronger a base is, the more strongly the formation of its conjugate acid is favored. The weaker an acid is, the stronger its conjugate base will be.
Under what conditions does it become necessary to use the quadratic equation to solve for [H₃O⁺] or pH?
When calculating [H₃O⁺] for weak acid solution whose % ionization is greater than 5%
Which of the following gives the correct mathematical operation required to calculate the [H₃O⁺] given a pH of 5.0?
[H₃O⁺] = 10⁻⁵∙⁰
Match the relative concentrations of hydronium and hydroxide with the type of solution. Acidic solution Basic solution Neutral solution
[H₃O⁺] > [OH⁻] [OH⁻] > [H₃O⁺] [H₃O⁺] = [OH⁻]
Which of the following options correctly represent the relationship between [H₃O⁺] and [OH⁻] in aqueous solutions at 25° C? Select all that apply.
[H₃O⁺][OH⁻] = 1.0 x 10⁻¹⁴ [H₃O⁺] = 1.0 x10⁻¹⁴ / [OH⁻]
According to ____ HI should be the strongest binary hydrohalic acid. In contrast, according to ____ HF should be the strongest binary hydrohalic acid. Since HI is the strongest binary hydrohalic acid, the predominant factor in determining acid strength of these species is _____.
bond enthalpy, polarity, bond enthalpy
The product of a Lewis acid-base reaction is a single species containing a new ______ bond. A + :B ⇌ A--B
covalent
When an ionic compound dissociates in water, the separated ions may react with H₂O to produce H₃O⁺ or OH⁻ ions. This process, known as salt _______, may affect the ______ of the salt solution.
hydrolysis pH
Oxoacids have the general formula illustrated, where the number of bonds to the central element E can vary. For the same element E, acid strength will _____ as the number of O atoms increases. For the same of O atoms, acid strength increases as the _____ of element E increases.
increases, electronegativity
The strength of an acid is measured by its tendency to _____ and form ____ ions in solution .
ionize hydrogen
Strong acids and bases are assumed to _____ completely in aqueous solution. Such a solution will conduct electricity well; strong acids and bases are therefore strong.
ionize electrolytes
A Bronsted base contain an atom with a(n) ______ pair of electrons in order to accept an H⁺.
lone
When [H₃O⁺] = [OH⁻], the solution is _____
neutral
Determine if aqueous solutions of the following salts are acidic, basic, or neutral. KBr NH₄ KCN
neutral acidic basic
The quantity -log[H₃O⁺] is called the _____ of a solution
pH
When a strong acid or base is added to a buffer system, there is a _____ change in the [HA]/[A-] ration and thus a ____ change in pH.
small; small
In the table shown, all acids listed above H₃O⁺ ______ acids, and all bases listed below OH⁻ _____ bases.
strong, strong
Acetic acid, CH₃COOH, is a _____acid compared to NH₃; hence, CH₃COO⁻ is a _____base than the amide ion, NH₂-.
stronger, weaker
If the molarity of a solution is given to 2 significant figures (e.g., 0.15 M), the pH value will be reported to _____ places after the decimal.
two
A(n)_______ acid is one that ionizes only slightly in water, whereas a(n) ______ acid ionizes completely into ions.
weak strong
Which of the following statements correctly describe the acid-base properties of a 0.10-M solution of ammonium cyanide (NH₄CN)? Select all that apply. Ka of NH₄⁺ = 5.6 x 10⁻¹⁰ and Kb of CN⁻ = 1.8 x 10⁻⁵.
-Both BH₄⁺ and CN⁻ will hydrlyze (react with water) in aqueous solution -The solution will be basic -CN⁻ will behave as a base when it reacts with water.
Match each stage of a weak acid-strong abuse titration with the correct description of how to calculate [H₃O⁺] and / or pH. initial pH before equivalence point at equivalence point after equivalence point
-Calculate [H₃O⁺] using Ka and [HA]initial -[H₃O⁺] = Ka x [HA] / [A⁻]; and [A⁻] determined using reaction table - Calculate [OH⁻] using Kb and [A⁻]; [H₃O⁺] = Kw / [OH⁻] -pH depends on excess base added
Match each species to the correct Lewis acid-base definition Lewis base Lewis acid
-Electron pair donor -Electron pair acceptor
Select all the statements that correctly describe the acid-base behavior of H₂O.
-In aqueous HCI, water acts as a Bronsted base -Water is amphoteric -In aqueous NH₃, water acts as a Bronsted acid
The pH of a salt solution containing a small, highly charged metal cation is influenced by the hydrolysis reaction of the metal ion. Which of the following statements correctly explain the hydrolysis reaction of these metal cations? Select all apply.
-Small, highly charged metal cations accept electron pairs from water molecules and form hydrated ions. -A hydrated metal ion produces an acidic solution because the metal ion withdraws electron density from the O-H bond, facilitating loss of H⁺.
Which of the following options correctly describe the structural characteristics of strong and weak bases? Select all that apply.
-Soluble hydroxides are strong bases. -Compounds that contain electron-rich N are weak bases.
Select all the statements that correctly describe the acid-base behavior of oxides.
-Some metals from Group 3A form amphoteric oxides. -Most nonmetal oxides are acidic -Alkali metal oxides are basic
Which of the following options correctly describe the behavior of acids and bases in aqueous solution? Select all that apply.
-Strong bases ionize completely in aqueous solution. -Strong acids and bases are electrolytes. -A weak acid ionizes to a limited extent in aqueous solution.
Consider two solutions of the weak acid HCN, one with concentration 0.010 M. Select the statements that correctly describe these solutions.
-The 0.10 M solution will have a higher [H₃O⁺] -The 0.010 M solution will have a higher percent ionization
Calculate and compare the pH values for 0.10 M solutions of NH₄Br (Ka 5.6 x 10⁻¹⁰) and Al(NO₃)₃ (Ka 1.3 x 10⁻⁵). Which of the following statements correctly describe the acidity of these solutions? Select all that apply.
-The NH₄Br solution has a higher pH than the Al(NO₃)₃ solution. -The pH of the Al(NO₃)₃ solution is 2.94
Which of the following statements correctly describe salt hydrolysis?
-The ions produced by dissociation of salt water react with H₂O. -Both the anion and the cation of a water-soluble salt may interact with water. -Salt hydrolysis causes the pH of the resulting solution to be above or below 7.00.
A 0.32 solution of phenol, which is weak monoprotic acid, has a pH of 5.22. Place the steps required to calculate the value of Ka for phenol in the correct order.
1) [H₃O⁺] = 10⁻⁵∙²² = 5.99 x 10⁻⁶ 2) Assume that [phenol] eq = 0.32 3) Ka = (5.99 x 10⁻⁶ /0.32)² = 1.12 x 10⁻¹⁰ 4) % ionization = 5.99 x 10⁻⁶ / 0.32 x 100 = 1.87 x 10⁻³ %, so the assumption is justified
Place the steps required to calculate the pH of a 0.10 M NaNo₂, solution in the correct order. Ka for KNO₂ is 4.5 x 10⁻⁴.
1)Kb for NO₂⁻ = 1.0 x 10⁻¹⁴ / 4.5 x 10⁻⁴ = 2.22 x 10⁻¹¹ 2) 2.22 x 20⁻¹¹ = [OH⁻][HNO₂] / [NO₂⁻ = x² / 0.10 3)[OH⁻] = 2/ (2.22 x 10⁻¹¹) x 0.10 4) pOH = -log(1.49 x10⁻⁶) = 5.82 5) pH = 14.00 - 5.82 = 8.17
Which of the following statements correctly describe the relationship between a weak acid or base and its conjugate base or acid?
1)The stronger a base is, the more strongly the formation of its conjugate acid is favored. 2) The weaker an acid is, the stronger its conjugate base will be.
Which of the following NH₃/NH₄⁺ buffer systems has the highest buffer capacity? Assume that equal volumes of the solutions are mixed in each case.
1.00 M NH₃/1.00 M NH₄⁺
A 0.10 M CH₃COOH solution has a [H₃O⁺] = 1.3 x 10⁻³ M. What is the percent ionization of CH₃COOH with a Ka = 1.8 x 10⁻⁵?
1.3%
The pH scale is a logarithmic scale, meaning that a solution with a pH of 1.00 has a concentration of hydronium (H₃O⁺) _____ times _____ than a solution with a pH of 3.00.
100; greater
Nitrous acid, HNO₂ has a Ka of 7.1 x 10⁻⁴. What is the [H₃O⁺] in a 0.60 M solution of HNO₂?
2.1 x 10⁻² M
Match each acid correctly to the number of ionizable protons: H₃PO₄, H₂CO₃, CH₃COOH
3 2 1
When calculation the pH of a weak acid solution it is justified to assume that [H₃O⁺] derived from the acid is negligible when the [H₃O+] is less than ______% of the initial acid concentration.
5
Calculate the Kb value for the acetate ion (CH₃COO⁻) if the Ka value for acetic acid (CH₃COOH) is 1.8 x 10⁻⁵.
5.6 x 10⁻¹₀
Which of the following structural characteristics must be present for a species to act as a Bronsted base?
An atom that has a lone pair of electrons
In what way is the titration curve for a weak base-strong acid titration similar to the titration curve for a weak acid-strong base titration?
Both have a buffer region before the equivalence point is reached.
Which of the following nonmetal oxides produce a weak acid dissolved in water? Select all that apply. N₂O₅ Cl₂O₇ CO₂ SO₃ P₄O₁₀
CO₂ P₄O₁₀
Which of the following anions will produce a neutral solution in water? Select all that apply, and assume that any associated cations do not affect the pH.
Cl⁻ NO3⁻ I⁻
Finding the pH of weak base solution is very similar to that for a weak acid. What is the only step that is necessary in the calculation of pH of a weak base and not a weak acid?
Convert [OH⁻] to [H₃O⁺]
Which of the protons depicted in the structure of acetic acid is considered acidic or ionizable? HA O l ll HB--C------C-------O------HD l Hc
D
True or false: The conjugate base of a weak acid will always be a strong base.
False
Which of the following statements correctly describe the relationship between the species in the reaction shown? Select all that apply HSO⁻₃ + CH₃NH₂ ⇌ SO₃²⁻ + CH₃NH₃⁺
HSO₃⁻ is the conjugate acid of SO₃²⁻. B and D are a conjugate acid-base pair. The base in the forward reaction is CH₃NH₂.
Which of the following compounds are strong acids? Select all that apply. HI HF H₂SO₄ HClO₄ HNO₂
Hl H₂SO₄ HClO₄
The autoionization of water is a process whereby water ionizes to a small extent to form ______ ions and ____ ions.
Hydronium and hydroxide
In the reaction illustrated here a proton is transferred from ___, which is the Bronsted ____ to ____, which acts as the Bronsted ______.
H₂O acid NH₃ base
Which statement best explains the trend in acid strength: H₂SO₄ > H₂SO₃ > H₂SeO₃
H₂SO₄ is stronger than H₂SO₃ because it has more O atoms
Match each acid with its correct Ka at 25° C given that HCN is the weakest and HF is the strongest of the acids listed. HCN CH₃COOH HF
Ka = 4.9 x 10⁻¹⁰ Ka = 1.8 x 10⁻⁵ Ka = 7.1 x 10⁻⁴
Select all the expressions that correctly express the relationship between Ka and Kb for a conjugate acid-base pair.
Ka = Kw/Kb Ka x Kb x Kw
In order to determine whether a solution of NH₄C₂H₃O₂ is acidic, basic, or neutral, what two values could be compared?
Ka of NH₄⁺ Kb of CH₃COO⁻
Which of the following quantities must be known in order to calculate the pH of an acid-base buffer solution using the Henderson-Hasselbalch equation? Select all that apply.
Ka of weak acid or Kb of weak base Concentration of conjugate base Concentration of weak acid
Which of the following correctly represents Kb for a weak base of general formula B?
Kb = [HB⁺][OH⁻] / [B}
Which of the following should be considered when selecting/ preparing a buffer solution? Select all that apply.
The buffer capacity will be higher if more concentrated solutions are used. The pKa of the acid component of the buffer should be close to the desired pH.
Why does the equivalence point for a weak base-strong acid titration occur at a pH < 7.00?
The conjugate acid of the weak base reacts with H₂O to give a solution with pH < 7.00.
Which statement most clearly explains the relationship between an acid and its conjugate base?
The conjugate base of a weak acid will react with water to a greater extent than the acid itself does.
Consider a buffer solution consisting of 0.35 M HNO₂ and 0.50 M KNO₂, which has an initial pH of 3.50 (Ka for HNO₂ = 4.5 x 10⁻⁴). If 0.03 mol of HCl are added to 1.0 L of this solution, which of the following options correctly reflects the steps required to calculate the change in pH? Select all that apply.
[H₃O⁺] prior to the addition of HCl = 4.5 x 10⁴ x 0.35 / 0.50 [NO₂⁻] after the addition of HCl is equal to 0.47 M. The final pH =3.34
Calculate the pH and [OH⁻] of a solution of a 1.5 M solution of HCI
[OH⁻] = 6.7 x 10⁻15 M pH = -0.18
Which of the following options correctly describe a solution with a pH =8.00? Select all that appl.
[OH⁻] > [H₃O⁺] The solution is basic
A salt in which the cation is the conjugate acid of a weak base will be _____. (Assume that the anion does not hydrolyze)
acidic
For real solutions, pH is defined as the negative logarithm of the _____ of the H⁺ ion. For dilute solutions, we use ____ in place of activity.
activity, concentration
An acid donates a proton to form its conjugate ________, which therefore has one less _______ atom and one more _______ charge than its acid.
base hydrogen negative
A salt in which the anion is the conjugate ______ of a weak _____ will produce a basic solution. (Assume that the cation does not hydrolyze.)
base, acid
In a Bronsted-Lowry acid-base reaction, the acid reacts to form its ________ _______ and the base will form its ______ _______
conjugate base conjugate acid
A Bronsted-Lowry acid is a proton ______and must therefore contain at least one ionizable ____atom in its formula
donor; hydrogen
An acid can be defined as a substance that loses one of more H⁺ ions when dissolved in water. An H⁺ ion is a hydrogen atom that has lost a(n)_______ and is therefore just a(n) _______. The H⁺ ion is not an isolated ion, but interacts strongly with H₂O to produce the ______ ion, which has the formula H₃O⁺.
electron proton hydronium
The point in a titration at which all of the acid has reacted with all of the base is called the ______ point.
equivalence
For a weak acid-strong base titration the pH at the equivalence point is ______
greater than 7.00
The pH at the equivalence point for a weak acid-strong base titration is _____ than 7.00 because at this point the major species in solution is the conjugate ______ of the weak acid. This species reacts with H₂O to form a(n) _________ solution.
greater; base; basic
Acidic solutions have a ____pOH than basic solutions.
higher
The stronger the acid, the ________ the [H₃O⁺] at equilibrium, and the _______ the value of Ka.
higher; larger
25.0 mL of 0.250 M HCl is titrated with a 0.125 M solution of the base aniline (C₆H₅NH₂;Kb = 3.80 x 10⁻¹⁰). The equivalence point is reached when 50.0 mL of base has been added. Which of the following options correctly reflect the steps required to calculate the pH at the equivalence point? Select all that apply.
pH = 2.82 Ka of the conjugate acid C₆H₅NH₃⁺ = 2.63 x 10⁻⁵ [C₆H₅NH₃⁺] at the equivalence point = 6.25 x 10⁻³ / 0.025 + 0.050 L = 8.33 x 10⁻² M
Match the following pH values with the type of aqueous solution at 25° C. Basic solution Neutral solution Acidic solution
pH > 7.00 pH = 7.00 pH < 7.00
In order to prepare a buffer with a specific pH value the ______ of the _____ component should be close to the desired pH.
pKa, acid
