Question 1

A buffer is prepared by adding 0.5 mol of solid sodium hydroxide to 1.0 L of 1.0 M acetic acid (CH₃COOH). What is the pH of the buffer? A)The pH will be pK _a - 0.30, where pK _a is that of acetic acid. B)The pH will be greater than the pK _a for acetic acid. C)The pH will be less than the value in answer a. D)The pH will be equal to the pK _a for acetic acid. E)More information is needed to solve the problem.

Accepted Answer

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Question 2

What will be the effect of adding 0.5 mL of 0.1 M NaOH to 100 mL of an acetate buffer in which [CH₃COOH] = [CH₃COO⁻] = 0.5 M? A)The pH will increase slightly. B)The pH will increase significantly. C)The pH will decrease slightly. D)The pH will decrease significantly. E)Since it is a buffer solution, the pH will not be affected.

Accepted Answer

Adding a small amount of NaOH (a weak base) to the acetate buffer (a weak acid) will result in a slight increase in pH. The buffer will resist large changes in pH, but a small amount of base will still cause a slight shift towards a more basic pH.

Question 3

A solution is prepared by adding 500 mL of 0.3 M NaClO to 500 mL of 0.4 M HClO. What is the pH of this solution? A)The pH will be greater than the pK _a of hypochlorous acid. B)The pH will be less than the pK _a of hypochlorous acid. C)The pH will be equal to the pK _a of hypochlorous acid. D)The pH will equal the pK _b of sodium hypochlorite. E)None of these choices are correct.

Accepted Answer

When NaClO and HClO are mixed, they react to form Na+ and ClO- ions along with H2O and Cl2 gas. The reaction consumes H+ ions and thus the pH of the resulting solution will be greater than the pH of pure HClO solution. The pKa of HClO is approximately 7.5, therefore a pH of less than 7.5 would indicate that the excess HClO is adding protons and increasing the acidity of the solution. Since the pH of the resulting solution is expected to be greater than 7.5, option A and C can be eliminated. The pKb of NaClO is approximately 4.74, therefore option D can also be eliminated. Thus, the best answer is B.

Question 4

A formic acid buffer containing 0.50 M HCOOH and 0.50 M HCOONa has a pH of 3.77. What will the pH be after 0.010 mol of NaOH has been added to 100.0 mL of the buffer?
A)3.67
B)3.78
C)3.81
D)3.85
E)3.95

Accepted Answer

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Question 5

What is the [H₃O⁺] in a solution that consists of 0.15 M C₂N₂H₈(ethylene diamine) and 0.35 C₂N₂H₉Cl? K_b = 4.7 × 10⁻⁴ A)2.0 × 10 ⁻³ M B)1.1 × 10 ⁻³ M C)6.3 × 10 ⁻⁹ M D)2.1 × 10 ⁻¹⁰ M E)5.0 × 10 ⁻¹¹ M

Accepted Answer

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Question 6

What is the [H₃O⁺] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? For HCOOH, K_a = 1.7 × 10⁻⁴ A)1.1 × 10 ⁻⁴ M B)2.6 × 10 ⁻⁴ M C)4.3 × 10 ⁻⁴ M D)6.7 × 10 ⁻⁵ M E)None of these choices are correct.

Accepted Answer

The concentration of H+ in the buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base (HCOONa) and [HA] is the concentration of the acid (HCOOH). Given pKa = -log(1.7 × 10^-5) and the concentrations, solving for [H+] gives approximately 2.6 × 10^-5 M.

Question 7

A buffer is prepared by adding 300.0 mL of 2.0 M NaOH to 500.0 mL of 2.0 M CH₃COOH. What is the pH of this buffer? K_a = 1.8 × 10⁻⁵ A)4.57 B)4.52 C)4.87 D)4.92 E)4.97

Accepted Answer

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Question 8

What is the pH of a buffer that consists of 0.20 M NaH₂PO₄and 0.40 M Na₂HPO₄? For NaH₂PO₄, K_a = 6.2 × 10⁻⁸ A)6.51 B)6.91 C)7.51 D)7.90 E)8.13

Accepted Answer

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Question 9

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the highest pH? A)[H ₂PO ₄ ⁻] = 0.50 M, [HPO ₄ ²⁻] = 0.50 M B)[H ₂PO ₄ ⁻] = 1.0 M, [HPO ₄ ²⁻] = 1.0 M C)[H₂PO₄⁻] = 1.0 M, [HPO₄²⁻] = 0.50 M D)[H₂PO₄⁻] = 0.50 M, [HPO₄²⁻] = 1.0 M E)[H ₂PO ₄ ⁻] = 0.75 M, [HPO ₄ ²⁻] = 1.0 M

Accepted Answer

The highest pH in a buffer solution is achieved when the concentration of the base component is higher than the acid component. In option D, the concentration of the base ([HPO4^2-]) is higher than the acid ([H2PO4^-]), which would result in a higher pH compared to the other options.

Question 10

What is the pH of a buffer that consists of 0.45 M CH₃COOH and 0.35 M CH₃COONa? K_a = 1.8 × 10⁻⁵ A)4.49 B)4.64 C)4.85 D)5.00 E)5.52

Accepted Answer

To find the pH of the buffer, we need to use the Henderson-Hasselbalch equation:

pH = pKa + log([conjugate base]/[acid])

The pKa is given as 1.8 × 10^-5. 
The acid is CH3COOH and the conjugate base is CH3COO-.

plugging in the given values, we get:

pH = 4.74 + log([0.35]/[0.45])
pH = 4.64

Therefore, the answer is B) 4.64.

Question 11

A buffer is prepared by adding 1.00 L of 1.0 M HCl to 750 mL of 1.5 M NaHCOO. What is the pH of this buffer? K_a = 1.7 × 10⁻⁴ A)2.87 B)3.72 C)3.82 D)3.95 E)4.66

Accepted Answer

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Question 12

What is the [H₃O⁺] in a solution that consists of 1.2 M HClO and 2.3 M NaClO? K_a = 3.5 × 10⁻⁸ A)7.8 × 10 ⁻⁹ M B)1.8 × 10 ⁻⁸ M C)6.7 × 10 ⁻⁸ M D)1.6 × 10 ⁻⁷ M E)None of these choices are correct.

Accepted Answer

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Question 13

What is the pH of a solution that consists of 0.50 M H₂C₆H₆O₆ (ascorbic acid) and 0.75 M NaHC₆H₆O₆(sodium ascorbate)? For ascorbic acid, K_a = 6.8 × 10⁻⁵ A)3.76 B)3.99 C)4.34 D)4.57 E)5.66

Accepted Answer

To solve this problem, we need to set up an equilibrium expression for the dissociation of ascorbic acid:

HS1U1B12S1U1B0CS1U1B16S1U1B0HS1U1B16S1U1B0OS1U1B16S1U1B0 ⇌ H+ + S1U1B12S1U1B0C6Hs1U1B38S1U1B0O6-

The Ka for this reaction is given as 6.8 x 10^-5, which allows us to calculate the concentration of H+ ions at equilibrium:

Ka = ([H+][S1U1B12S1U1B0C6Hs1U1B38S1U1B0O6-])/[HS1U1B12S1U1B0CS1U1B16S1U1B0HS1U1B16S1U1B0OS1U1B16S1U1B0]

6.8 x 10^-5 = (x^2)/(0.50 - x)

Using the quadratic equation or an ICE table, we find that x = 1.03 x 10^-3 M.

The overall concentration of ascorbate is 0.75 M, so we can assume the concentration of HS1U1B12S1U1B0CS1U1B16S1U1B0HS1U1B16S1U1B0OS1U1B16S1U1B0 is essentially constant at 0.75 M (since it is a weak base and won't react substantially with water). Thus, the pH of the solution is:

pH = -log[H+] = -log(1.03 x 10^-3) = 3.99

Therefore, the answer is choice B.

Question 14

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the lowest pH? A)[CH₃COOH] = 0.25 M, [CH₃COO⁻] = 0.25 M B)[CH ₃COOH] = 0.75 M, [CH ₃COO ⁻] = 0.75 M C)[CH ₃COOH] = 0.75 M, [CH ₃COO ⁻] = 0.25 M D)[CH ₃COOH] = 0.25 M, [CH ₃COO ⁻] = 0.75 M E)[CH ₃COOH] = 1.00 M, [CH ₃COO ⁻] = 1.00 M

Accepted Answer

The pH of a buffer solution is determined by the ratio of the concentration of the conjugate base to the concentration of the weak acid. Buffer solutions with a higher concentration of weak acid and a lower concentration of conjugate base will have a lower pH. In this case, option C has a higher concentration of weak acid (0.75 M) and a lower concentration of conjugate base (0.25 M) compared to option A (concentrations are equal) and option B and D (higher concentration of both weak acid and conjugate base). Therefore, option C should have the lowest pH. Option E is not a buffer solution as the concentrations are not in a proper ratio to act as a buffer.

Question 15

A buffer is prepared by adding 100 mL of 0.50 M sodium hydroxide to 100 mL of 0.75 M propanoic acid. Is this a buffer solution, and if so, what is its pH? A)It is a buffer, pH > pK _a of propanoic acid. B)It is a buffer, pH < pK _a of propanoic acid. C)It is a buffer, pH = pK _a of propanoic acid. D)It is a buffer, pH = pK _b of sodium propanoate. E)Since sodium hydroxide is a strong base, this is not a buffer.

Accepted Answer

To determine if this is a buffer solution, we need to calculate the pH and compare it to the pKa of propanoic acid. 
The balanced equation for the reaction is:
CH3CH2COOH + NaOH --> CH3CH2COONa + H2O

To calculate the moles of each species present, we use the formula n = c x V.
n(NaOH) = 0.50 mol/L x 0.10 L = 0.05 mol
n(propanoic acid) = 0.75 mol/L x 0.10 L = 0.075 mol

Since NaOH completely dissociates in solution, we have 0.05 mol of OH- ions. 
These will react with the propanoic acid to form the conjugate base, sodium propanoate, and water:

OH- + CH3CH2COOH --> CH3CH2COO- + H2O

The amount of propanoic acid that reacts with the OH- ions is determined by the amount of sodium propanoate that is formed:

n(NaCH3CH2COO) = n(NaOH) = 0.05 mol

The amount of propanoic acid remaining is therefore:

n(CH3CH2COOH) = 0.075 - 0.05 = 0.025 mol

To calculate the concentrations of the conjugate acid and base, we divide the moles by the total volume of the solution (200 mL, or 0.2 L):

[CH3CH2COOH] = 0.025 mol / 0.2 L = 0.125 M
[CH3CH2COO-] = 0.05 mol / 0.2 L = 0.25 M

To determine the pH of the buffer, we use the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

The pKa of propanoic acid is 4.87.

pH = 4.87 + log(0.25/0.125) 
pH = 4.87 + 0.30 
pH = 5.17

Since the pH is greater than the pKa, this is a buffer solution. Therefore, choice A is correct.

Question 16

What is the pK_a for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75? A)< 4.00 B)4.63 C)4.87 D)5.02 E)> 5.50

Accepted Answer

First, we need to set up the equation for the dissociation of HA:

HA ⇌ H+ + A-

Then, we can use the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

We know the pH (4.75) and the molarities of A- and HA in the solution. We can use the molarities to calculate the ratio [A-]/[HA]:

[A-]/[HA] = 0.85/0.65 = 1.31

Now we can rearrange the Henderson-Hasselbalch equation to solve for pKa:

pKa = pH - log([A-]/[HA])
pKa = 4.75 - log(1.31)
pKa = 4.63

Therefore, the answer is B.

Question 17

An acetic acid buffer containing 0.50 M CH₃COOH and 0.50 M CH₃COONa has a pH of 4.74. What will the pH be after 0.0020 mol of HCl has been added to 100.0 mL of the buffer? A)4.77 B)4.71 C)4.68 D)4.62 E)None of these choices are correct.

Accepted Answer

The buffer solution resists changes in pH. When HCl is added, it reacts with the acetate ion (CH3COO-) to form acetic acid (CH3COOH), slightly increasing the concentration of acetic acid and decreasing the concentration of acetate ion. Using the Henderson-Hasselbalch equation, the pH change is minimal, resulting in a pH of approximately 4.71.

Question 18

A solution is prepared by adding 100 mL of 0.2 M hydrochloric acid to 100 mL of 0.4 M sodium formate. Is this a buffer solution, and if so, what is its pH? A)It is a buffer, pH > pK _a of formic acid. B)It is a buffer, pH < pK _a of formic acid. C)It is a buffer, pH = pK _a of formic acid. D)It is a buffer, pH = pK _b of sodium formate. E)Since hydrochloric acid is a strong acid, this is not a buffer.

Accepted Answer

The solution is a buffer because it contains a weak acid (formic acid) and its conjugate base (sodium formate). The pH of the buffer can be calculated using the Henderson-Hasselbalch equation:pH = pK _a + log([A-]/[HA])where pK _a is the dissociation constant of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.In this case, the pK _a of formic acid is 3.75. The concentration of the conjugate base is 0.1 M (since 100 mL of 0.4 M sodium formate was added to 100 mL of water), and the concentration of the weak acid is 0.1 M (since 100 mL of 0.2 M hydrochloric acid was added to 100 mL of water).Substituting these values into the Henderson-Hasselbalch equation, we get:pH = 3.75 + log(0.1/0.1) = 3.75Therefore, the pH of the buffer is 3.75, which is equal to the pK _a of formic acid.

Question 19

What will be the effect of adding 0.5 mL of 0.1 M HCl to 100 mL of a phosphate buffer in which [H₂PO₄⁻] = [HPO₄²⁻] = 0.35 M? A)The pH will increase slightly. B)The pH will increase significantly. C)The pH will decrease slightly. D)The pH will decrease significantly. E)Since it is a buffer solution, the pH will not be affected.

Accepted Answer

When HCl is added to the buffer solution, it will react with the basic form of the buffer (HS1U1B12S1U1B0POS1U1B14S1U1B0S1U1P1−S1S1P0) to form its conjugate acid form H2S1U1B12S1U1B0POS1U1B14S1U1B0S1U1P1−S1S1P0S1U1P1H. This reaction will decrease the concentration of the basic form of the buffer and increase the concentration of the acidic form of the buffer, causing a slight decrease in the pH of the buffer solution. Therefore, the correct choice is C.

Question 20

What is the [H₃O⁺] in a solution that consists of 1.5 M NH₃and 2.5 NH₄Cl? K_b = 1.8 × 10⁻⁵ A)1.1 × 10 ⁻⁵ M B)3.0 × 10 ⁻⁶ M C)3.3 × 10 ⁻⁹ M D)9.3 × 10 ⁻¹⁰ M E)None of these choices are correct.

Accepted Answer

The answer of What is the [H₃O⁺] in a solution...

Quiz 19: Ionic Equilibria in Aqueous Systems

A buffer is prepared by adding 0.5 mol of solid sodium hydroxide to 1.0 L of 1.0 M acetic acid (CH₃COOH) . What is the pH of the buffer?

What will be the effect of adding 0.5 mL of 0.1 M NaOH to 100 mL of an acetate buffer in which [CH₃COOH] = [CH₃COO⁻] = 0.5 M?

A solution is prepared by adding 500 mL of 0.3 M NaClO to 500 mL of 0.4 M HClO. What is the pH of this solution?

A formic acid buffer containing 0.50 M HCOOH and 0.50 M HCOONa has a pH of 3.77. What will the pH be after 0.010 mol of NaOH has been added to 100.0 mL of the buffer?

What is the [H₃O⁺] in a solution that consists of 0.15 M C₂N₂H₈(ethylene diamine) and 0.35 C₂N₂H₉Cl? K_b = 4.7 × 10⁻⁴

What is the [H₃O⁺] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? For HCOOH, K_a = 1.7 × 10⁻⁴

A buffer is prepared by adding 300.0 mL of 2.0 M NaOH to 500.0 mL of 2.0 M CH₃COOH. What is the pH of this buffer? K_a = 1.8 × 10⁻⁵

What is the pH of a buffer that consists of 0.20 M NaH₂PO₄and 0.40 M Na₂HPO₄? For NaH₂PO₄, K_a = 6.2 × 10⁻⁸

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the highest pH?

What is the pH of a buffer that consists of 0.45 M CH₃COOH and 0.35 M CH₃COONa? K_a = 1.8 × 10⁻⁵

A buffer is prepared by adding 1.00 L of 1.0 M HCl to 750 mL of 1.5 M NaHCOO. What is the pH of this buffer? K_a = 1.7 × 10⁻⁴

What is the [H₃O⁺] in a solution that consists of 1.2 M HClO and 2.3 M NaClO? K_a = 3.5 × 10⁻⁸

What is the pH of a solution that consists of 0.50 M H₂C₆H₆O₆ (ascorbic acid) and 0.75 M NaHC₆H₆O₆(sodium ascorbate) ? For ascorbic acid, K_a = 6.8 × 10⁻⁵

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the lowest pH?

A buffer is prepared by adding 100 mL of 0.50 M sodium hydroxide to 100 mL of 0.75 M propanoic acid. Is this a buffer solution, and if so, what is its pH?

What is the pK_a for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75?

An acetic acid buffer containing 0.50 M CH₃COOH and 0.50 M CH₃COONa has a pH of 4.74. What will the pH be after 0.0020 mol of HCl has been added to 100.0 mL of the buffer?

A solution is prepared by adding 100 mL of 0.2 M hydrochloric acid to 100 mL of 0.4 M sodium formate. Is this a buffer solution, and if so, what is its pH?

What will be the effect of adding 0.5 mL of 0.1 M HCl to 100 mL of a phosphate buffer in which [H₂PO₄⁻] = [HPO₄²⁻] = 0.35 M?

What is the [H₃O⁺] in a solution that consists of 1.5 M NH₃and 2.5 NH₄Cl? K_b = 1.8 × 10⁻⁵

Quiz 19: Ionic Equilibria in Aqueous Systems

A buffer is prepared by adding 0.5 mol of solid sodium hydroxide to 1.0 L of 1.0 M acetic acid (CH3COOH) . What is the pH of the buffer?

What will be the effect of adding 0.5 mL of 0.1 M NaOH to 100 mL of an acetate buffer in which [CH3COOH] = [CH3COO−] = 0.5 M?

A solution is prepared by adding 500 mL of 0.3 M NaClO to 500 mL of 0.4 M HClO. What is the pH of this solution?

A formic acid buffer containing 0.50 M HCOOH and 0.50 M HCOONa has a pH of 3.77. What will the pH be after 0.010 mol of NaOH has been added to 100.0 mL of the buffer?

What is the [H3O+] in a solution that consists of 0.15 M C2N2H8 (ethylene diamine) and 0.35 C2N2H9Cl? Kb = 4.7 × 10−4

What is the [H3O+] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? For HCOOH, Ka = 1.7 × 10−4

A buffer is prepared by adding 300.0 mL of 2.0 M NaOH to 500.0 mL of 2.0 M CH3COOH. What is the pH of this buffer? Ka = 1.8 × 10−5

What is the pH of a buffer that consists of 0.20 M NaH2PO4 and 0.40 M Na2HPO4? For NaH2PO4, Ka = 6.2 × 10−8

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the highest pH?

What is the pH of a buffer that consists of 0.45 M CH3COOH and 0.35 M CH3COONa? Ka = 1.8 × 10−5

A buffer is prepared by adding 1.00 L of 1.0 M HCl to 750 mL of 1.5 M NaHCOO. What is the pH of this buffer? Ka = 1.7 × 10−4

What is the [H3O+] in a solution that consists of 1.2 M HClO and 2.3 M NaClO? Ka = 3.5 × 10−8

What is the pH of a solution that consists of 0.50 M H2C6H6O6 (ascorbic acid) and 0.75 M NaHC6H6O6 (sodium ascorbate) ? For ascorbic acid, Ka = 6.8 × 10−5

Buffer solutions with the component concentrations shown below were prepared. Which of them should have the lowest pH?

A buffer is prepared by adding 100 mL of 0.50 M sodium hydroxide to 100 mL of 0.75 M propanoic acid. Is this a buffer solution, and if so, what is its pH?

What is the pKa for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75?

An acetic acid buffer containing 0.50 M CH3COOH and 0.50 M CH3COONa has a pH of 4.74. What will the pH be after 0.0020 mol of HCl has been added to 100.0 mL of the buffer?

A solution is prepared by adding 100 mL of 0.2 M hydrochloric acid to 100 mL of 0.4 M sodium formate. Is this a buffer solution, and if so, what is its pH?

What will be the effect of adding 0.5 mL of 0.1 M HCl to 100 mL of a phosphate buffer in which [H2PO4−] = [HPO42−] = 0.35 M?

What is the [H3O+] in a solution that consists of 1.5 M NH3 and 2.5 NH4Cl? Kb = 1.8 × 10−5

A buffer is prepared by adding 0.5 mol of solid sodium hydroxide to 1.0 L of 1.0 M acetic acid (CH₃COOH) . What is the pH of the buffer?

What will be the effect of adding 0.5 mL of 0.1 M NaOH to 100 mL of an acetate buffer in which [CH₃COOH] = [CH₃COO⁻] = 0.5 M?

What is the [H₃O⁺] in a solution that consists of 0.15 M C₂N₂H₈(ethylene diamine) and 0.35 C₂N₂H₉Cl? K_b = 4.7 × 10⁻⁴

What is the [H₃O⁺] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa? For HCOOH, K_a = 1.7 × 10⁻⁴

A buffer is prepared by adding 300.0 mL of 2.0 M NaOH to 500.0 mL of 2.0 M CH₃COOH. What is the pH of this buffer? K_a = 1.8 × 10⁻⁵

What is the pH of a buffer that consists of 0.20 M NaH₂PO₄and 0.40 M Na₂HPO₄? For NaH₂PO₄, K_a = 6.2 × 10⁻⁸

What is the pH of a buffer that consists of 0.45 M CH₃COOH and 0.35 M CH₃COONa? K_a = 1.8 × 10⁻⁵

A buffer is prepared by adding 1.00 L of 1.0 M HCl to 750 mL of 1.5 M NaHCOO. What is the pH of this buffer? K_a = 1.7 × 10⁻⁴

What is the [H₃O⁺] in a solution that consists of 1.2 M HClO and 2.3 M NaClO? K_a = 3.5 × 10⁻⁸

What is the pH of a solution that consists of 0.50 M H₂C₆H₆O₆ (ascorbic acid) and 0.75 M NaHC₆H₆O₆(sodium ascorbate) ? For ascorbic acid, K_a = 6.8 × 10⁻⁵

What is the pK_a for the acid HA if a solution of 0.65 M HA and 0.85 M NaA has a pH of 4.75?

An acetic acid buffer containing 0.50 M CH₃COOH and 0.50 M CH₃COONa has a pH of 4.74. What will the pH be after 0.0020 mol of HCl has been added to 100.0 mL of the buffer?

What will be the effect of adding 0.5 mL of 0.1 M HCl to 100 mL of a phosphate buffer in which [H₂PO₄⁻] = [HPO₄²⁻] = 0.35 M?

What is the [H₃O⁺] in a solution that consists of 1.5 M NH₃and 2.5 NH₄Cl? K_b = 1.8 × 10⁻⁵