17. Acid and Base Equilibrium

Ka and Kb

16.5 pH Calculations for Weak Acids and Bases | General Chemistry

Calculate Kb values for CH3COO- and ClO-.

Associated with any weak acid or weak base is a Ka or Kb value respectively.&#160;

Write the chemical equation and the Kb expression for the reaction of each of the following bases with water: (a) propylamine, C3H7NH2

Understanding Ka and Kb Expressions

 This pH would be correct only from a strong acid with this concentration. 

Correct use of the Ka expression.

Set up an ICE table using the initial concentration of the acid given and x to represent the changes in this 1:1:1 stoichiometry reaction. Then solve the Ka expression for x.

This is the value of the pKa for this acid.

 This calculation involves a square root in finding the final answer. 

 Set the calculation up as equilibrium problem and use the hydronium ion concentration to determine the pH. 

Determine the pH of 0.450 M HC7H5O2. The Ka for HC7H5O2 is 6.5 &#215; 10&#8722;5.

Which is the stronger base, the acetate ion or the hypochlorite
ion?

HCNO (Ka = 2.0 x 10-4)

HF (Ka = 3.5 x 10-4)

HN3 (Ka = 2.5 x 10-5)

H2CO3 (Ka = 4.3 x 10-7)

Which Bronsted-Lowry acid has the weakest conjugate base?

The following picture represents the hydrated metal cation 
M1H2O26 
n + , where n = 1, 2, or 3. 
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/9b21e5c68c74879f-1672920887286.jpg" alt="" /> 
(b) Does the equilibrium constant increase, decrease, or remain 
the same as the value of n increases? Explain.

Which, if any, of the following statements are true? 
(a) The stronger the base, the smaller the pKb. 
(b) The stronger the base, the larger the pKb. 
(c) The stronger the base, the smaller the Kb. 
(d) The stronger the base, the larger the Kb. 
(e) The stronger the base, the smaller the pKa of its conjugate acid. 
(f) The stronger the base, the larger the pKa of its conjugate acid.

Use the acid-dissociation constants in Table 16.3 to arrange these oxyanions from strongest base to weakest: SO42-, CO32-, SO32-, and PO43-.

The following pictures represent solutions of three salts 
NaA (A- = X-, Y-, or Z-); water molecules and Na+ ions 
have been omitted for clarity. 
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/6edeff97da172255-1672925646549.jpg" alt="" /> 
(c) Which A- anion has the smallest value of pKb?

Acid/Base Dissociation Constant

Ka and Kb Example 1

Write equations showing how each weak base ionizes water to
form OH-. Also write the corresponding expression for Kb.
b. C6H5NH2

Rank the solutions in order of decreasing [H3O+]: 0.10 M HCl;
0.10 M HF; 0.10 M HClO; 0.10 M HC6H5O.

Using values of Kb in Appendix C, calculate values of Ka for
each of the following ions.
(a) Propylammonium ion, C3H7NH3+

The following picture represents the hydrated metal cation
M1H2O26
n + , where n = 1, 2, or 3.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/4cf065bdf6b8879e-1672682728616.jpg" alt="" />
(a) Write a balanced equation for the reaction of M1H2O26
n + with water and write the equilibrium equation for the
reaction.

Understanding Ka and Kb

Butyric acid is responsible for the foul smell of rancid butter. The pKa of butyric acid is 4.84. (a) Calculate the pKb for the butyrate ion.

Which of the following solutions will have the lowest pH

Write equations showing how each weak base ionizes water to
form OH-. Also write the corresponding expression for Kb.
c. C2H5NH2

The Kb for methylamine 1CH3NH22 at 25 °C is given in Appendix D. (a) Write the chemical equation for the equilibrium that corresponds to Kb.

The Ka for the ammonium ion must be calculated based on the Kb for ammonia.

 Correct, the ammonium ion acts as an acid. 

 The solution will not be neutral since this salt contains a weak acid. 

The Ka for the ammonium ion must be calculated based on the Kb for ammonia.

 The salt of a weak base will act as a weak acid. 

What is the pH of a 0.250 M NH4Cl solution? Kb for NH3 = 1.8 &#215; 10&#8722;5.

Write a balanced net ionic equation and the corresponding 
equilibrium equation for the reaction of the following weak 
bases with water. 
(c) Cyanide ion, CN

The greater the Ka value then the stronger the acid, while the greater the Kb the stronger the base. Ka and Kb are connected by the following equation:&#160;

If the Kb&nbsp;of NH3 is 1.76 x 10-5, determine the acid dissociation constant of its conjugate acid.&nbsp;

 A small amount of ionization would produce fewer products. 

 The forward reaction is not the predominant reaction in the ionization of a weak acid. 

 Correct, there are fewer products at equilibrium in the ionization of a weak acid. 

K is a ratio of products to reactants.

The Ka value for a weak acid is _________ than the Ka value for a strong acid because the weak acid ionizes to a _________ extent than the strong acid.

Using values of Ka in Appendix C, calculate values of Kb for 
each of the following ions. 
(a) Fluoride ion, F-

The following diagrams represent aqueous solutions of
three acids, HX, HY, and HZ. The water molecules have been
omitted for clarity, and the hydrated proton is represented
as H+ rather than H3O+.(b) Which acid would have the smallest aciddissociation
constant, Ka?
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/63ea71301863afd8-1667225805890.jpg" alt="" />

Using dissociation constants from Appendix D, determine the value for the equilibrium constant for each of the following reactions.
(i) HCO3-1aq2 + OH-1aq2 ΔCO32-1aq2 + H2O1l2
(ii) NH4+1aq2 + CO32-1aq2 ΔNH31aq2 + HCO3-1aq2

Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (b) Using Appendix D, calculate the Ka for pyridinium bromide.

Write the chemical equation and the Ka expression for the acid dissociation of each of the following acids in aqueous solution. First show the reaction with H+1aq2 as a product and then with the hydronium ion: (a) C6H5COOH

Classify each acid as strong or weak. If the acid is weak, write an
expression for the acid ionization constant (Ka).
d. H2CO3

Write equations showing how each weak base ionizes water to
form OH-. Also write the corresponding expression for Kb.
a. CO32-

Nicotine 1C10H14N22 can accept two protons because it has
two basic N atoms 1Kb1 = 1.0 * 10-6; Kb2 = 1.3 * 10-112.
Calculate the values of Ka for the conjugate acids
C10H14N2H+ and C10H14N2H22 + .

Given that Kb for ammonia is 1.8 * 10-5 and that for hydroxylamine is 1.1 * 10-8, which is the stronger base?

C2H8N2(Kb = 8.3 x 10-5)

C5H5N (Kb = 1.7 x 10-9)

(CH3)3N (Kb = 1.0 x 10-6)

C3H7NH2(Kb = 3.5 x 10-4)

C6H5NH2(Kb = 3.9 x 10-10)

Which Bronsted-Lowry base has the greatest concentration of hydroxide ions?&nbsp;

What is the equilibrium constant for the following reaction and determine if reactants or products are favored

The amino acid glycine 1H2N¬CH2¬COOH2 can participate in the following equilibria in water:
H2N¬CH2¬COOH + H2OΔ H2N¬CH2¬COO- + H3O+ Ka = 4.3 * 10-3

H2N¬CH2¬COOH + H2OΔ+H3N¬CH2¬COOH + OH- Kb = 6.0 * 10-5

(a) Use the values of Ka and Kb to estimate the equilibrium constant for the intramolecular proton transfer to form a zwitterion: H2N¬CH2¬COOH Δ +H3N¬CH2¬COO-

Choose from the conjugate acid–base pairs HSO4- >SO42-,
HF>F-, and NH4+>NH3 to complete the following equation
with the pair that gives an equilibrium constant Kc 7 1.
_____ + NO2 - S _____ + HNO2

Set up an ICE table using the initial concentration of the base given and x to represent the changes in this 1:1:1 stoichiometry reaction. Then solve the Kb expression for x which is equal to [OH&#8722;].

 Correct, the solution is distinctly basic. 

 This would be the pH if pyridine were a strong base. 

 Set the calculation up as equilibrium problem and use the hydroxide ion concentration to determine the pH. 

Calculate the pH of a 0.500 M pyridine (C5H5N) solution. Kb value for pyridine is 1.7 &#215; 10&#8722;9.

The hypochlorite ion, ClO-, acts as a weak base. (a) Is ClO- a stronger or weaker base than hydroxylamine?

Write the chemical equation and the Kb expression for the reaction of each of the following bases with water: (c) benzoate ion, C6H5CO2-

Weak acids possess a Ka value less than 1, while weak bases possess a Kb value less than 1. The equilibrium expressions of Ka and Kb are the same as other equilibrium constants we&#8217;ve seen.&#160;

Salts containing the phosphate ion are added to municipal 
water supplies to prevent the corrosion of lead pipes. (a) Based 
on the pKa values for phosphoric acid 1pKa1 = 7.5 * 10 - 3, 
pKa2 = 6.2 * 10 - 8, pKa3 = 4.2 * 10 - 132 what is the Kb 
value for the PO43 - ion?

Ka and acid strength | Chemical processes | MCAT | Khan Academy

Given that Ka for acetic acid is 1.8 * 10-5 and that for 
hypochlorous acid is 3.0 * 10-8, which is the stronger acid?

Acids and Bases - Basic Introduction - Chemistry

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Ionic Salts

Polyprotic Acid

A&#160;polyprotic acid&#160;possesses more than 2 hydronium ions (H+).&#160;

Diprotic Acid

A diprotic acid&#160;is an acid that can donate two hydronium ions (H+).&#160;