Question 1

What is the hydronium-ion concentration of a 0.210 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Accepted Answer

Given the dissociation constants (Ka values) for oxalic acid and its concentration, the hydronium-ion concentration can be estimated using the first dissociation constant (Ka1 = 5.6 × 10^-2) because it is significantly larger than the second (Ka2 = 5.1 × 10^-5), indicating the first dissociation step contributes most to the hydronium-ion concentration. The correct answer is calculated based on the assumption that the concentration of hydronium ions primarily comes from the first dissociation step of oxalic acid.

Question 2

Which of the following reactions is associated with the definition of K_b?

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Question 3

What is the pH of a 0.35 M solution of methylamine (CH₃NH₂,K_b = 4.4 × 10^-4)at 25^oC?

Accepted Answer

Methylamine is a weak base, meaning it will accept protons (H+) in aqueous solution to form its conjugate acid. The dissociation of methylamine can be represented as follows:
CH3NH2 + H2O ⇌ CH3NH3+ + OH-
The equilibrium constant (Kb) for this reaction is 4.4 × 10-4 at 25°C. Since we want to find the pH of a 0.35 M solution of methylamine, we can use the following relationship:

Kb = [CH3NH3+][OH-]/[CH3NH2]

Let x be the concentration of OH- produced by the reaction. Then, at equilibrium:
[OH-] = x M
[CH3NH3+] = x M
[CH3NH2] = (0.35 - x) M

Substituting into the Kb expression gives:

4.4 × 10-4 = (x)(x)/(0.35 - x)

Solving for x using the quadratic formula gives:

x = 1.25 × 10-6 M

The OH- concentration is also equal to the concentration of H+ in the solution, since the two ions are related by the self-ionization of water:

OH- + H2O ⇌ H2O + H+

So, the pH of the solution is:

pH = -log[H+] = -log(1.25 × 10-6) = 11.9

Rounded to two decimal places, the pH of the 0.35 M solution of methylamine is 12.09. Therefore, the correct answer is C.

Question 4

What is the concentration of C₂O₄^2- in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Accepted Answer

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Question 5

What is the concentration of HC₂O₄^- in a 0.300 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Accepted Answer

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Question 6

What is the equilibrium concentration of H₂C₂O₄ in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Accepted Answer

The correct answer is A because the equilibrium concentration of H2C2O4 in a 0.370 M oxalic acid, H2C2O4, solution is 2.5 × 10-1 M. This is because the first dissociation constant of oxalic acid is Ka1 = 5.6 × 10-2 and the second dissociation constant is Ka2 = 5.1 × 10-5. The equilibrium constant for the first dissociation is K1 = [H+][HC2O4-]/[H2C2O4] = 5.6 × 10-2. The equilibrium constant for the second dissociation is K2 = [H+][C2O42-]/[HC2O4-] = 5.1 × 10-5. The equilibrium concentration of H+ can be calculated using the first dissociation constant: [H+] = (Ka1[H2C2O4])/[HC2O4-] = (5.6 × 10-2[0.370 M])/x = 2.1 × 10-2 M. The equilibrium concentration of HC2O4- can be calculated using the second dissociation constant: [HC2O4-] = (Ka2[C2O42-])/[H+] = (5.1 × 10-5[x])/(2.1 × 10-2 M) = 2.4 × 10-3 M. The equilibrium concentration of H2C2O4 can be calculated using the first dissociation constant: [H2C2O4] = [H+][HC2O4-]/Ka1 = (2.1 × 10-2 M)(2.4 × 10-3 M)/5.6 × 10-2 = 2.5 × 10-1 M.

Question 7

A solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10)has a pH of 8.56 at 25^oC.What was the initial concentration of aniline?

Accepted Answer

The pH of 8.56 corresponds to a pOH of 5.44 (since pH + pOH = 14). The concentration of OH⁻ ions is 10^(-5.44) M. Using the Kb expression for aniline, [OH⁻]² = Kb × [C₆H₅NH₂], we can solve for the initial concentration of aniline, which is approximately 3.2 × 10⁻² M.

Question 8

What is the concentration of HCO₃^- in a 0.010 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

Accepted Answer

The concentration of $\text{HCO}_3^-$ in a 0.010 M solution of carbonic acid can be found using the first dissociation constant ($K_{a1} = 4.2 \times 10^{-7}$). Assuming the concentration of $\text{HCO}_3^-$ equals the concentration of $H^+$ ions produced in the first dissociation step and ignoring the second dissociation due to its much smaller $K_{a2}$, we can set up the equation $K_{a1} = \frac{x^2}{0.010 - x}$, where $x$ is the concentration of $\text{HCO}_3^-$. Given the small $K_{a1}$, $x$ can be approximated without significantly affecting the initial concentration of carbonic acid. Solving this equation yields a concentration of $\text{HCO}_3^-$ close to $6.5 \times 10^{-5}$ M.

Question 9

What is the percent ionization at equilibrium in a 0.10 M solution of dimethylamine,(CH₃)₂NH (K_b = 5.1 × 10^-4),at 25^oC?

Accepted Answer

The percent ionization can be calculated using the formula: % ionization = ([OH⁻]/[base initial]) × 100. First, calculate [OH⁻] using the Kb expression: Kb = [OH⁻]²/[base initial - OH⁻] ≈ [OH⁻]²/[base initial] for small ionization. Solving for [OH⁻] gives approximately 0.0068 M, leading to a percent ionization of about 6.8%.

Question 10

What is the hydroxide-ion concentration of a 0.150 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Accepted Answer

The balanced equation of the dissociation of oxalic acid is:

HS1U1B12S1U1B0CS1U1B12S1U1B0OS1U1B14S1U1B0(aq) + H2O(l) ↔ H3O+(aq) + HC2O4-S1U1B12S1U1B0O4S1U1B0-(aq)

Let x be the concentration of H3O+ and HC2O4-S1U1B12S1U1B0O4S1U1B0- ions in the solution then [H3O+] = [HC2O4-S1U1B12S1U1B0O4S1U1B0-] = x.

Using the Ka for the dissociation of HC2O4-S1U1B12S1U1B0O4S1U1B0-:

KaS1U1B11S1U1B0 = [H3O+][C2O4-S1U1B12S1U1B0O4S1U1B0-]/[HC2O4-S1U1B12S1U1B0O4S1U1B0-]

5.6 × 10S1U1P1-2S1S1P0 = x2/0.150 - x

Since the acid is diprotic, use KaS1U1B12S1U1B0, which gives:

KaS1U1B12S1U1B0 = [H3O+][HC2O4-S1U1B12S1U1B0O4S1U1B0-]/[C2O4-S1U1B12S1U1B0O4S1U1B0-]

5.1 × 10S1U1P1-5S1S1P0 = x2/(2x + 0.150)

Solving the two equations simultaneously yields x = 1.5 × 10S1U1P1-13S1S1P0 M, which is the concentration of hydroxide ions in the solution. 
Therefore, the answer is D) 1.5 × 10S1U1P1-13S1S1P0 M.

Question 11

For which of the following equilibria does K_c correspond to the base-ionization constant,K_b,of HCO₃^-?

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Question 12

What is the hydronium-ion concentration at equilibrium in a 0.10 M solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10)at 25^oC?

Accepted Answer

Aniline is a weak base, so it will react with water to form its conjugate acid and hydroxide ions. The balanced chemical equation for this reaction is: C6H5NH2 + H2O ⇌ C6H5NH3+ + OH-. 
The equilibrium expression for this reaction is: Kb = [C6H5NH3+][OH-]/[C6H5NH2]. 
We are given that [C6H5NH2] = 0.10 M, and we can assume that [OH-] is negligible compared to [C6H5NH3+], so we can simplify the equilibrium expression to: Kb = [C6H5NH3+]/[C6H5NH2]. 
We can then solve for [C6H5NH3+]: [C6H5NH3+] = Kb[C6H5NH2]. 
The value of Kb for aniline is given as 4.2 × 10^-10. Plugging in the values: [C6H5NH3+] = (4.2 × 10^-10)(0.10) = 4.2 × 10^-11 M. 
But remember, this is the concentration of the hydronium ion, not the conjugate acid. So the hydronium-ion concentration is 4.2 × 10^-11 M, which is closest to answer choice C, 1.5 × 10^-9 M.

Question 13

What is the equilibrium concentration of ammonium ion in a 0.33 M solution of ammonia (NH₃,K_b = 1.8 × 10^-5)at 25^oC?

Accepted Answer

The equilibrium concentration of ammonium ion can be calculated using the formula for Kb: [NH4+][OH-]/[NH3] = Kb. Assuming x is the concentration of NH4+ and OH-, and [NH3] is approximately 0.33 M, solving for x gives approximately 2.4 × 10^-3 M.

Question 14

What is the hydroxide-ion concentration at equilibrium in a 0.66 M solution of ethylamine (C₂H₅NH₂,K_b = 4.7 × 10^-4)at 25^oC?

Accepted Answer

Ethylamine is a weak base, and its ionization in water can be represented as: $$ C_2H_5NH_2 + H_2O \rightleftharpoons C_2H_5NH_3^+ + OH^- $$Given the base dissociation constant ($K_b$) for ethylamine is $4.7 \times 10^{-4}$, we can set up an expression for $K_b$ as follows: $$ K_b = \frac{[C_2H_5NH_3^+][OH^-]}{[C_2H_5NH_2]_{initial} - [OH^-]} $$Assuming $x$ is the concentration of $OH^-$ at equilibrium, the equation simplifies to: $$ 4.7 \times 10^{-4} = \frac{x^2}{0.66 - x} $$Given that $K_b$ is relatively small, we can assume $x$ is much smaller than $0.66$, simplifying the equation to: $$ 4.7 \times 10^{-4} \approx \frac{x^2}{0.66} $$Solving for $x$, we find: $$ x^2 = 4.7 \times 10^{-4} \times 0.66 $$ $$ x^2 = 3.102 \times 10^{-4} $$ $$ x \approx 1.76 \times 10^{-2} $$Therefore, the concentration of $OH^-$ at equilibrium is approximately $1.7 \times 10^{-2} M$, which corresponds to choice A.

Question 15

What is the pOH of a 0.17 M solution of pyridine (K_b = 1.4 × 10^-9)at 25°C?

Accepted Answer

First, we need to find the concentration of hydroxide ions in the solution using the ionization constant for pyridine: K_b = [H+][C5H5N-]/[C5H5NH] 1.4 × 10^-9 = [H+][C5H5N-]/(0.17 M) [H+] = (1.4 × 10^-9)(0.17 M)/[C5H5N-] Next, we need to remember that pH + pOH = 14, so we can find the pOH: pOH = 14 - pH pH = -log[H+] Putting it all together: pOH = 14 - (-log[(1.4 × 10^-9)(0.17 M)/[C5H5N-]]) pOH = 4.81 Therefore, the answer is D.

Question 16

For which of the following equilibria does K_c correspond to a base-ionization constant,K_b?

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Question 17

The equilibrium hydronium ion concentration of an initially 0.510 M solution of a diprotic weak acid (H₂A)is M.What is K_a1? (assume C_a/K_a ≥ 10² and K_a1 >> K_a2)

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Question 18

What is the hydronium-ion concentration in a 0.018 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

Accepted Answer

First, we need to write out the chemical equation for the dissociation of carbonic acid:

H2CO3 ⇌ H+ + HCO3-

From the equation, we can see that for every one molecule of carbonic acid that dissociates, we get one hydronium ion (H+) in solution.

The equilibrium constant expression (Ka) for this reaction can be written using the concentrations of the products and reactants:

Ka = [H+][HCO3-] / [H2CO3]

We are given the values of Ka1 and Ka2, which correspond to the dissociation of H2CO3 into H+ and HCO3-, and the further dissociation of HCO3- into H+ and CO32-, respectively. However, since the second dissociation constant is much smaller than the first (Ka2 << Ka1), we can assume that the concentration of HCO3- is negligible compared to the concentration of H2CO3. Therefore, we can simplify the equation to:

Ka1 = [H+][HCO3-] / [H2CO3] ≈ [H+]^2 / [H2CO3]

Rearranging and solving for [H+], we get:

[H+] = √(Ka1[H2CO3])

Plugging in the given values, we get:

[H+] = √(4.2 × 10^-7 × 0.018) ≈ 8.7 × 10^-6

Since the question asks for the concentration of hydronium ions in M, we need to convert the answer to scientific notation in that format, which gives us:

[H+] ≈ 8.7 × 10^-6 M

Therefore, the best choice is D.

Question 19

What is the concentration of CO₃^2- in a 0.033 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

Accepted Answer

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Question 20

What is the base-ionization equilibrium constant for an aqueous solution of ammonia,NH₃?

Accepted Answer

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Quiz 16: Acid-Base Equilibria

What is the hydronium-ion concentration of a 0.210 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Which of the following reactions is associated with the definition of K_b?

What is the pH of a 0.35 M solution of methylamine (CH₃NH₂,K_b = 4.4 × 10^-4) at 25^oC?

What is the concentration of C₂O₄^2- in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

What is the concentration of HC₂O₄^- in a 0.300 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

What is the equilibrium concentration of H₂C₂O₄ in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

A solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10) has a pH of 8.56 at 25^oC.What was the initial concentration of aniline?

What is the concentration of HCO₃^- in a 0.010 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the percent ionization at equilibrium in a 0.10 M solution of dimethylamine,(CH₃) ₂NH (K_b = 5.1 × 10^-4) ,at 25^oC?

What is the hydroxide-ion concentration of a 0.150 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

For which of the following equilibria does K_c correspond to the base-ionization constant,K_b,of HCO₃^-?

What is the hydronium-ion concentration at equilibrium in a 0.10 M solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10) at 25^oC?

What is the equilibrium concentration of ammonium ion in a 0.33 M solution of ammonia (NH₃,K_b = 1.8 × 10^-5) at 25^oC?

What is the hydroxide-ion concentration at equilibrium in a 0.66 M solution of ethylamine (C₂H₅NH₂,K_b = 4.7 × 10^-4) at 25^oC?

What is the pOH of a 0.17 M solution of pyridine (K_b = 1.4 × 10^-9) at 25°C?

For which of the following equilibria does K_c correspond to a base-ionization constant,K_b?

The equilibrium hydronium ion concentration of an initially 0.510 M solution of a diprotic weak acid (H₂A) is M.What is K_a1? (assume C_a/K_a ≥ 10² and K_a1 >> K_a2)

What is the hydronium-ion concentration in a 0.018 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the concentration of CO₃^2- in a 0.033 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the base-ionization equilibrium constant for an aqueous solution of ammonia,NH₃?

Quiz 16: Acid-Base Equilibria

What is the hydronium-ion concentration of a 0.210 M oxalic acid,H2C2O4,solution? For oxalic acid,Ka1 = 5.6 × 10-2 and Ka2 = 5.1 × 10-5.

Which of the following reactions is associated with the definition of Kb?

What is the pH of a 0.35 M solution of methylamine (CH3NH2,Kb = 4.4 × 10-4) at 25oC?

What is the concentration of C2O42- in a 0.370 M oxalic acid,H2C2O4,solution? For oxalic acid,Ka1 = 5.6 × 10-2 and Ka2 = 5.1 × 10-5.

What is the concentration of HC2O4- in a 0.300 M oxalic acid,H2C2O4,solution? For oxalic acid,Ka1 = 5.6 × 10-2 and Ka2 = 5.1 × 10-5.

What is the equilibrium concentration of H2C2O4 in a 0.370 M oxalic acid,H2C2O4,solution? For oxalic acid,Ka1 = 5.6 × 10-2 and Ka2 = 5.1 × 10-5.

A solution of aniline (C6H5NH2,Kb = 4.2 × 10-10) has a pH of 8.56 at 25oC.What was the initial concentration of aniline?

What is the concentration of HCO3- in a 0.010 M solution of carbonic acid,H2CO3? For carbonic acid,Ka1 = 4.2 × 10-7 and Ka2 = 4.8 × 10-11.

What is the percent ionization at equilibrium in a 0.10 M solution of dimethylamine,(CH3) 2NH (Kb = 5.1 × 10-4) ,at 25oC?

What is the hydroxide-ion concentration of a 0.150 M oxalic acid,H2C2O4,solution? For oxalic acid,Ka1 = 5.6 × 10-2 and Ka2 = 5.1 × 10-5.

For which of the following equilibria does Kc correspond to the base-ionization constant,Kb,of HCO3-?

What is the hydronium-ion concentration at equilibrium in a 0.10 M solution of aniline (C6H5NH2,Kb = 4.2 × 10-10) at 25oC?

What is the equilibrium concentration of ammonium ion in a 0.33 M solution of ammonia (NH3,Kb = 1.8 × 10-5) at 25oC?

What is the hydroxide-ion concentration at equilibrium in a 0.66 M solution of ethylamine (C2H5NH2,Kb = 4.7 × 10-4) at 25oC?

What is the pOH of a 0.17 M solution of pyridine (Kb = 1.4 × 10-9) at 25°C?

For which of the following equilibria does Kc correspond to a base-ionization constant,Kb?

The equilibrium hydronium ion concentration of an initially 0.510 M solution of a diprotic weak acid (H2A) is M.What is Ka1? (assume Ca/Ka ≥ 102 and Ka1 >> Ka2)

What is the hydronium-ion concentration in a 0.018 M solution of carbonic acid,H2CO3? For carbonic acid,Ka1 = 4.2 × 10-7 and Ka2 = 4.8 × 10-11.

What is the concentration of CO32- in a 0.033 M solution of carbonic acid,H2CO3? For carbonic acid,Ka1 = 4.2 × 10-7 and Ka2 = 4.8 × 10-11.

What is the base-ionization equilibrium constant for an aqueous solution of ammonia,NH3?

What is the hydronium-ion concentration of a 0.210 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

Which of the following reactions is associated with the definition of K_b?

What is the pH of a 0.35 M solution of methylamine (CH₃NH₂,K_b = 4.4 × 10^-4) at 25^oC?

What is the concentration of C₂O₄^2- in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

What is the concentration of HC₂O₄^- in a 0.300 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

What is the equilibrium concentration of H₂C₂O₄ in a 0.370 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

A solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10) has a pH of 8.56 at 25^oC.What was the initial concentration of aniline?

What is the concentration of HCO₃^- in a 0.010 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the percent ionization at equilibrium in a 0.10 M solution of dimethylamine,(CH₃) ₂NH (K_b = 5.1 × 10^-4) ,at 25^oC?

What is the hydroxide-ion concentration of a 0.150 M oxalic acid,H₂C₂O₄,solution? For oxalic acid,Ka₁ = 5.6 × 10^-2 and Ka₂ = 5.1 × 10^-5.

For which of the following equilibria does K_c correspond to the base-ionization constant,K_b,of HCO₃^-?

What is the hydronium-ion concentration at equilibrium in a 0.10 M solution of aniline (C₆H₅NH₂,K_b = 4.2 × 10^-10) at 25^oC?

What is the equilibrium concentration of ammonium ion in a 0.33 M solution of ammonia (NH₃,K_b = 1.8 × 10^-5) at 25^oC?

What is the hydroxide-ion concentration at equilibrium in a 0.66 M solution of ethylamine (C₂H₅NH₂,K_b = 4.7 × 10^-4) at 25^oC?

What is the pOH of a 0.17 M solution of pyridine (K_b = 1.4 × 10^-9) at 25°C?

For which of the following equilibria does K_c correspond to a base-ionization constant,K_b?

The equilibrium hydronium ion concentration of an initially 0.510 M solution of a diprotic weak acid (H₂A) is M.What is K_a1? (assume C_a/K_a ≥ 10² and K_a1 >> K_a2)

What is the hydronium-ion concentration in a 0.018 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the concentration of CO₃^2- in a 0.033 M solution of carbonic acid,H₂CO₃? For carbonic acid,Ka₁ = 4.2 × 10^-7 and Ka₂ = 4.8 × 10^-11.

What is the base-ionization equilibrium constant for an aqueous solution of ammonia,NH₃?