Question 1

What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of NaCN? Assume that the volumes of the solutions are additive and that K_a =

Accepted Answer

The balanced chemical equation for the reaction between HCN and NaCN in water is: HCN + NaCN + H2O -> H3O+ + CN- + Na+ Since Na+ is a spectator ion and does not participate in the acid-base equilibrium, we can ignore it in our calculations. The initial concentrations of HCN and CN- are given by: [HCN] = 0.10 M [CN-] = 0.10 M * (50.00 mL / 100.00 mL) * (1 L / 1000 mL) / K_a = 9.1 × 10^-10 M (using the given value of K_a = 3.9 × 10^-10) Assuming that the solution is well-mixed and the volume does not change upon mixing, the final volume is 100.00 mL and the final concentration of H3O+ is given by: [H3O+] = [CN-] + Ka * [HCN] = 9.1 × 10^-10 M + (1.0 × 10^-9) * (0.10 M) = 1.2 × 10^-9 M Therefore, the hydronium ion concentration in the solution is 1.2 × 10^-9 M, which is closest to choice (C).

Question 2

Calculate the pH of a buffer that is 0.115 M HC₂H₃O₂ and 0.160 M KC₂H₃O₂.The K_a for HC₂H₃O₂ is 1.8 × 10^-5.

Accepted Answer

The correct answer is A because the pH of a buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]), where pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid. In this case, the pKa of HC2H3O2 is 1.8 × 10-5, [A-] = 0.160 M, and [HA] = 0.115 M. Plugging these values into the equation gives pH = 1.8 × 10-5 + log(0.160/0.115) = 4.89.

Question 3

Which of the following acids (listed with pK_a values)and their conjugate base would form a buffer with a pH of 8.10?

Accepted Answer

A buffer solution is most effective when the pH is close to the pK_a of the acid. The pK_a of HClO is 7.54, which is closest to the desired pH of 8.10.

Question 4

Calculate the pH of a buffer that is 0.080 M HF and 0.040 M NaF.The K_a for HF is 3.5 × 10^-4.

Accepted Answer

First, we need to calculate the pKa of HF: 
pKa = -log(Ka) 
pKa = -log(3.5 × 10^-4) 
pKa = 3.46

Next, we need to use the Henderson-Hasselbalch equation to calculate the pH of the buffer: 
pH = pKa + log([A^-]/[HA]) 
pH = 3.46 + log(0.040/0.080) 
pH = 3.16

Therefore, the pH of the buffer is 3.16, which is option C.

Question 5

A 1.0 L buffer solution is 0.050 M HC₂H₃O₂ and 0.250 M KC₂H₃O₂.Which of the following actions will destroy the buffer?

Accepted Answer

Adding 0.050 moles of NaOH will react with the acetic acid, potentially depleting it and destroying the buffer capacity.

Question 6

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M NH₃ with 10.00 mL of 0.10 M NH₄Cl? Assume that the volume of the solutions are additive and that K_b = 1.8 × 10^-5for NH₃.

Accepted Answer

First, we need to use the equation for calculating the pH of a weak base solution: pH = pKb + log([base]/[acid]), where Kb is the base dissociation constant, [base] is the concentration of the base, and [acid] is the concentration of the conjugate acid.

Since we are given the concentration of the base (NHS1U1B13S1U1B0) and the volume of the solution, we can calculate the moles of base present:

moles of base = (50.00 mL)(0.10 mol/L) = 5.00 × 10S1U1P1-4 mol

Next, we need to calculate the concentration of the conjugate acid (NHS1U1B14S1U1B0Cl) using the balanced chemical equation for the reaction between the two compounds:

NHS1U1B13S1U1B0 + HCl → NHS1U1B14S1U1B0Cl

From the equation, we can see that 1 mole of NHS1U1B13S1U1B0 reacts with 1 mole of HCl to form 1 mole of NHS1U1B14S1U1B0Cl. Therefore, the moles of acid present in the solution are:

moles of acid = (10.00 mL)(0.10 mol/L) = 1.00 ×10S1U1P1-4 mol

Since the volumes of the solutions are additive, the total volume of the solution is:

total volume = 50.00 mL + 10.00 mL = 60.00 mL = 0.060 L

Using the moles of base and acid and the total volume, we can calculate their concentrations:

[base] = moles of base/total volume = 5.00 × 10S1U1P1-4 mol/0.060 L = 8.33 × 10S1U1P1-3 M

[acid] = moles of acid/total volume = 1.00 × 10S1U1P1-4 mol/0.060 L = 1.67 × 10S1U1P1-3 M

Finally, we can plug all of these values into the pH equation:

pH = pKb + log([base]/[acid]) = -log(Kb) + log([base]/[acid])

Since the problem states that KS1U1B1bS1U1B0 = 1.8 × 10S1U1P1-5 S1S1P0for NHS1U1B13S1U1B0, we can calculate Kb as:

Kb = Kw/Ka = 1.0 × 10S1U1P1-14/1.8 × 10S1U1P1-5 = 5.56 × 10S1U1P1-10

Plugging in all the values:

pH = -log(Kb) + log([base]/[acid]) = -log(5.56 × 10S1U1P1-10) + log(8.33 × 10S1U1P1-3/1.67 × 10S1U1P1-3) = 9.95

Therefore, the pH of the solution is 9.95, which corresponds to choice C.

Question 7

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M methylamine,CH₃NH₂,with 15.00 mL of 0.10 M methylammonium chloride,CH₃NH₃Cl? Assume that the volume of the solutions are additive and that K_b = 3.70 × 10^-4 for methylamine.

Accepted Answer

First, we need to write the chemical equation for the reaction between methylamine and methylammonium chloride:

CH3NH2 + CH3NH3Cl  →  CH3NH3+ + CH3NH2Cl-

The equilibrium constant for this reaction, K, is given by:

K = [CH3NH3+][CH3NH2Cl-] / [CH3NH2][CH3NH3Cl]

At equilibrium, the concentration of CH3NH2 will be reduced by x, the concentration of CH3NH3+ and CH3NH2Cl- will both increase by x, and the concentration of CH3NH3Cl will be reduced by x. Therefore, at equilibrium:

[CH3NH2] = 0.1 - x
[CH3NH3Cl] = 0.1 - x
[CH3NH3+] = [CH3NH2Cl-] = x

Substituting these values into the equilibrium constant expression gives:

K = x^2 / [(0.1 - x)(0.1 - x)]

Assuming that x is small compared to 0.1, we can approximate the denominator as 0.01 and simplify the expression:

K = x^2 / 0.01

Taking the square root of both sides and substituting the given value of K gives:

x = sqrt(K * 0.01) = sqrt(3.70 × 10^-4 * 0.01) = 1.92 × 10^-3

Therefore:

[CH3NH2] = 0.1 - x = 0.1 - 1.92 × 10^-3 = 0.0971 M
[OH-] = x = 1.92 × 10^-3 M

The pOH of the solution is:

pOH = -log[OH-] = -log(1.92 × 10^-3) = 2.72

Finally, we can calculate the pH:

pH = 14 - pOH = 14 - 2.72 = 11.28

This is closest to choice C (11.09).

Question 8

You wish to prepare an HC₂H₃O₂ buffer with a pH of 5.24.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

Accepted Answer

The Henderson-Hasselbalch equation is used to calculate the ratio of the concentrations of the conjugate base to the acid: pH = pKa + log([A-]/[HA]). Solving for the ratio: 5.24 = 4.74 + log([A-]/[HA]), gives [A-]/[HA] = 3.16.

Question 9

A buffer solution is 0.100 M in both HC₇H₅O₂ and NaC₇H₅O₂ and has a pH of 4.19.Which of the following pH values would you expect from the addition of a small amount of a dilute solution of a strong base?

Accepted Answer

The addition of a strong base to a buffer solution will slightly increase the pH. Since the initial pH is 4.19, the pH will increase slightly, making 4.49 a reasonable expectation.

Question 10

Calculate the pH of a buffer that is 1.58 M HClO and 0.099 M NaClO.The K_a for HClO is 2.9 × 10^-8.

Accepted Answer

The answer of Calculate the pH of a buffer that...

Question 11

Calculate the pH of a buffer that is 0.040 M HF and 0.080 M NaF.The K_a for HF is 3.5 × 10^-4.

Accepted Answer

The answer of Calculate the pH of a buffer that...

Question 12

A 1.0 L buffer solution is 0.250 M HC₂H₃O₂ and 0.050 M NaC₂H₃O₂.Which of the following actions will destroy the buffer?

Accepted Answer

Adding HCl will destroy the buffer as it will react with the HC₂H₃O₂ to form more HCl, leading to a decrease in the buffer capacity. All other options involve adding more of the components already present in the buffer, which will maintain the buffer capacity.

Question 13

Which of the following acids (listed with K_a values)and their conjugate base would form a buffer with a pH of 2.34?

Accepted Answer

To form a buffer with a pH of 2.34, we need an acid with a pKa close to 2.34. The conjugate base of this acid should also be able to act as a buffer at this pH. Looking at the given options, only Option E has a pKa value close to 2.34 (pKa = 1.12) and can form a buffer with its conjugate base HClO2 (pKa = 2.0). Therefore, the best choice is E.

Question 14

The highest pH for an effective buffer occurs when the base is how many times as concentrated as the acid?

Accepted Answer

The Henderson-Hasselbalch equation is pH = pKa + log([A-]/[HA]). At the maximum pH for an effective buffer, the pH equals the pKa of the conjugate acid/base pair. Therefore, we can rewrite the Henderson-Hasselbalch equation as pH = pKa + log([base]/[acid]). At the maximum pH, the log([base]/[acid]) term is equal to zero. Therefore, we need to have equal concentrations of acid and base. Since we want the base to be more concentrated, the answer is 10 times as concentrated, or choice C.

Question 15

Identify the most common indicator.

Accepted Answer

Phenolphthalein is one of the most commonly used indicators in acid-base titrations due to its clear color change from colorless to pink over a pH range of 8.2 to 10.0.

Question 16

Calculate the pH of a buffer that is 0.032 M HF and 0.032 M KF.The K_a for HF is 3.5 × 10^-4.

Accepted Answer

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). Here, [A-] = [KF] = 0.032 M and [HA] = [HF] = 0.032 M. The pKa is calculated as -log(Ka) = -log(3.5 × 10^-4) ≈ 3.46. Since [A-] = [HA], log([A-]/[HA]) = log(1) = 0. Thus, pH = pKa = 3.46.

Question 17

What is the pH of a solution prepared by mixing 100.00 mL of 0.020 M Ca(OH)₂ with 50.00 mL of 0.100 M NaOH? Assume that the volumes are additive.

Accepted Answer

The answer of What is the pH of a solution...

Question 18

What is the [CH₃CO₂-]/[CH₃CO₂H] ratio necessary to make a buffer solution with a pH of 4.44? K_a = 1.8 × 10^-5for CH₃CO₂H.

Accepted Answer

The answer of What is the [CH₃CO₂-]/[CH₃CO₂H] ratio necessary to...

Question 19

You wish to prepare an HC₂H₃O₂ buffer with a pH of 4.14.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

Accepted Answer

To calculate the ratio of [C₂⁻]/[HC₂H₃O₂], we can use the Henderson-Hasselbalch equation: pH = pK_a + log([C₂⁻]/[HC₂H₃O₂]) 4.14 = 4.74 + log([C₂⁻]/[HC₂H₃O₂]) -0.60 = log([C₂⁻]/[HC₂H₃O₂]) We can then take the anti-log of both sides to eliminate the log term: 0.25 = [C₂⁻]/[HC₂H₃O₂] Therefore, the ratio of [C₂⁻]/[HC₂H₃O₂] that should be used is 0.25, or 1:4.

Question 20

What is the pH of a buffer system prepared by dissolving 10.70 grams of NH₄Cl and 35.00 mL of 12 M NH₃ in enough water to make 1.000 L of solution? K_b = 1.80 × 10^-5for NH₃.

Accepted Answer

The answer of What is the pH of a buffer...

Quiz 18: Aqueous Ionic Equilibrium

What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of NaCN? Assume that the volumes of the solutions are additive and that K_a =

Calculate the pH of a buffer that is 0.115 M HC₂H₃O₂ and 0.160 M KC₂H₃O₂.The K_a for HC₂H₃O₂ is 1.8 × 10^-5.

Which of the following acids (listed with pK_a values) and their conjugate base would form a buffer with a pH of 8.10?

Calculate the pH of a buffer that is 0.080 M HF and 0.040 M NaF.The K_a for HF is 3.5 × 10^-4.

A 1.0 L buffer solution is 0.050 M HC₂H₃O₂ and 0.250 M KC₂H₃O₂.Which of the following actions will destroy the buffer?

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M NH₃ with 10.00 mL of 0.10 M NH₄Cl? Assume that the volume of the solutions are additive and that K_b = 1.8 × 10^-5for NH₃.

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M methylamine,CH₃NH₂,with 15.00 mL of 0.10 M methylammonium chloride,CH₃NH₃Cl? Assume that the volume of the solutions are additive and that K_b = 3.70 × 10^-4 for methylamine.

You wish to prepare an HC₂H₃O₂ buffer with a pH of 5.24.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

A buffer solution is 0.100 M in both HC₇H₅O₂ and NaC₇H₅O₂ and has a pH of 4.19.Which of the following pH values would you expect from the addition of a small amount of a dilute solution of a strong base?

Calculate the pH of a buffer that is 1.58 M HClO and 0.099 M NaClO.The K_a for HClO is 2.9 × 10^-8.

Calculate the pH of a buffer that is 0.040 M HF and 0.080 M NaF.The K_a for HF is 3.5 × 10^-4.

A 1.0 L buffer solution is 0.250 M HC₂H₃O₂ and 0.050 M NaC₂H₃O₂.Which of the following actions will destroy the buffer?

Which of the following acids (listed with K_a values) and their conjugate base would form a buffer with a pH of 2.34?

The highest pH for an effective buffer occurs when the base is how many times as concentrated as the acid?

Identify the most common indicator.

Calculate the pH of a buffer that is 0.032 M HF and 0.032 M KF.The K_a for HF is 3.5 × 10^-4.

What is the pH of a solution prepared by mixing 100.00 mL of 0.020 M Ca(OH) ₂ with 50.00 mL of 0.100 M NaOH? Assume that the volumes are additive.

What is the [CH₃CO₂-]/[CH₃CO₂H] ratio necessary to make a buffer solution with a pH of 4.44? K_a = 1.8 × 10^-5for CH₃CO₂H.

You wish to prepare an HC₂H₃O₂ buffer with a pH of 4.14.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

What is the pH of a buffer system prepared by dissolving 10.70 grams of NH₄Cl and 35.00 mL of 12 M NH₃ in enough water to make 1.000 L of solution? K_b = 1.80 × 10^-5for NH₃.

Quiz 18: Aqueous Ionic Equilibrium

What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of NaCN? Assume that the volumes of the solutions are additive and that Ka =

Calculate the pH of a buffer that is 0.115 M HC2H3O2 and 0.160 M KC2H3O2.The Ka for HC2H3O2 is 1.8 × 10-5.

Which of the following acids (listed with pKa values) and their conjugate base would form a buffer with a pH of 8.10?

Calculate the pH of a buffer that is 0.080 M HF and 0.040 M NaF.The Ka for HF is 3.5 × 10-4.

A 1.0 L buffer solution is 0.050 M HC2H3O2 and 0.250 M KC2H3O2.Which of the following actions will destroy the buffer?

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M NH3 with 10.00 mL of 0.10 M NH4Cl? Assume that the volume of the solutions are additive and that Kb = 1.8 × 10-5 for NH3.

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M methylamine,CH3NH2,with 15.00 mL of 0.10 M methylammonium chloride,CH3NH3Cl? Assume that the volume of the solutions are additive and that Kb = 3.70 × 10-4 for methylamine.

You wish to prepare an HC2H3O2 buffer with a pH of 5.24.If the pKa of is 4.74,what ratio of C2H3O2⁻/HC2H3O2 must you use?

A buffer solution is 0.100 M in both HC7H5O2 and NaC7H5O2 and has a pH of 4.19.Which of the following pH values would you expect from the addition of a small amount of a dilute solution of a strong base?

Calculate the pH of a buffer that is 1.58 M HClO and 0.099 M NaClO.The Ka for HClO is 2.9 × 10-8.

Calculate the pH of a buffer that is 0.040 M HF and 0.080 M NaF.The Ka for HF is 3.5 × 10-4.

A 1.0 L buffer solution is 0.250 M HC2H3O2 and 0.050 M NaC2H3O2.Which of the following actions will destroy the buffer?

Which of the following acids (listed with Ka values) and their conjugate base would form a buffer with a pH of 2.34?

The highest pH for an effective buffer occurs when the base is how many times as concentrated as the acid?

Identify the most common indicator.

Calculate the pH of a buffer that is 0.032 M HF and 0.032 M KF.The Ka for HF is 3.5 × 10-4.

What is the pH of a solution prepared by mixing 100.00 mL of 0.020 M Ca(OH) 2 with 50.00 mL of 0.100 M NaOH? Assume that the volumes are additive.

What is the [CH3CO2-]/[CH3CO2H] ratio necessary to make a buffer solution with a pH of 4.44? Ka = 1.8 × 10-5 for CH3CO2H.

You wish to prepare an HC2H3O2 buffer with a pH of 4.14.If the pKa of is 4.74,what ratio of C2H3O2⁻/HC2H3O2 must you use?

What is the pH of a buffer system prepared by dissolving 10.70 grams of NH4Cl and 35.00 mL of 12 M NH3 in enough water to make 1.000 L of solution? Kb = 1.80 × 10-5 for NH3.

What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of NaCN? Assume that the volumes of the solutions are additive and that K_a =

Calculate the pH of a buffer that is 0.115 M HC₂H₃O₂ and 0.160 M KC₂H₃O₂.The K_a for HC₂H₃O₂ is 1.8 × 10^-5.

Which of the following acids (listed with pK_a values) and their conjugate base would form a buffer with a pH of 8.10?

Calculate the pH of a buffer that is 0.080 M HF and 0.040 M NaF.The K_a for HF is 3.5 × 10^-4.

A 1.0 L buffer solution is 0.050 M HC₂H₃O₂ and 0.250 M KC₂H₃O₂.Which of the following actions will destroy the buffer?

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M NH₃ with 10.00 mL of 0.10 M NH₄Cl? Assume that the volume of the solutions are additive and that K_b = 1.8 × 10^-5for NH₃.

What is the pH of a solution prepared by mixing 50.00 mL of 0.10 M methylamine,CH₃NH₂,with 15.00 mL of 0.10 M methylammonium chloride,CH₃NH₃Cl? Assume that the volume of the solutions are additive and that K_b = 3.70 × 10^-4 for methylamine.

You wish to prepare an HC₂H₃O₂ buffer with a pH of 5.24.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

A buffer solution is 0.100 M in both HC₇H₅O₂ and NaC₇H₅O₂ and has a pH of 4.19.Which of the following pH values would you expect from the addition of a small amount of a dilute solution of a strong base?

Calculate the pH of a buffer that is 1.58 M HClO and 0.099 M NaClO.The K_a for HClO is 2.9 × 10^-8.

Calculate the pH of a buffer that is 0.040 M HF and 0.080 M NaF.The K_a for HF is 3.5 × 10^-4.

A 1.0 L buffer solution is 0.250 M HC₂H₃O₂ and 0.050 M NaC₂H₃O₂.Which of the following actions will destroy the buffer?

Which of the following acids (listed with K_a values) and their conjugate base would form a buffer with a pH of 2.34?

Calculate the pH of a buffer that is 0.032 M HF and 0.032 M KF.The K_a for HF is 3.5 × 10^-4.

What is the pH of a solution prepared by mixing 100.00 mL of 0.020 M Ca(OH) ₂ with 50.00 mL of 0.100 M NaOH? Assume that the volumes are additive.

What is the [CH₃CO₂-]/[CH₃CO₂H] ratio necessary to make a buffer solution with a pH of 4.44? K_a = 1.8 × 10^-5for CH₃CO₂H.

You wish to prepare an HC₂H₃O₂ buffer with a pH of 4.14.If the pK_a of is 4.74,what ratio of C₂H₃O₂⁻/HC₂H₃O₂ must you use?

What is the pH of a buffer system prepared by dissolving 10.70 grams of NH₄Cl and 35.00 mL of 12 M NH₃ in enough water to make 1.000 L of solution? K_b = 1.80 × 10^-5for NH₃.