Question 1

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 10. Which of the following indicator acids would be best to use to mark the endpoint of this titration?

Accepted Answer

The best indicator for a titration is one whose pKa is close to the pH at the equivalence point. For a pH of 10, an indicator with a pKa of around 10 is ideal. Indicator B, with a Ka of 10^-11, has a pKa of 11, which is closest to the desired pH.

Question 2

A 200.0-mL sample of the weak acid HS1U1B13S1U1B0A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
-After 350.0 mL of 0.200 M NaOH is added

Accepted Answer

After adding 350.0 mL of 0.200 M NaOH to 200.0 mL of 0.100 M weak acid, the solution is beyond the equivalence point. The major species are OH⁻ from the excess NaOH and A³⁻, the fully deprotonated form of the acid.

Question 3

Consider the following information about the diprotic acid ascorbic acid (HS1U1B12S1U1B0As for short, molar mass = 176.1).  The titration curve for disodium ascorbate, NaS1U1B12S1U1B0As, with standard HCl is shown below: 
-Which of the following is a major species present at point IV?

Accepted Answer

The answer of Consider the following information about the diprotic...

Question 4

A 200.0-mL sample of the weak acid HS1U1B13S1U1B0A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
-After 200.0 mL of 0.200 M NaOH is added

Accepted Answer

The answer of A 200.0-mL sample of the weak acid...

Question 5

A certain indicator HIn has a pK_a of 9.00, and a color change becomes visible when 7.00% of it is In^-. At what pH is this color change visible?

Accepted Answer

The pK_a of the indicator is 9.00, which means the equilibrium constant for the reaction HIn ⇌ In^- + H+ is 10^-9.00. At the pH where 7.00% of the indicator is in the anionic form (In^-), the equilibrium constant for the reaction is 10^-2.853, which is equal to ([In^-]/[HIn]). By solving this equation, the pH is found to be 7.88. Therefore, the correct answer is B.

Question 6

After adding 25.0 mL of 0.100 M NaOH to 100.0 mL of 0.100 M weak acid (HA), the pH is found to be 5.90. Determine the value of K_a for the acid HA.

Accepted Answer

The correct answer is A because the pH of the solution is 5.90, which means that the concentration of H+ ions is 1.00 x 10^-5.90 M. The concentration of HA can be calculated using the ICE table:```HA + NaOH -> NaA + H2OInitial: 0.100 M 0.100 M 0Change: -0.025 M -0.025 M +0.025 MEquilibrium: 0.075 M 0.075 M 0.025 M```The Ka expression is:```Ka = [H+][A-]/[HA]```Substituting the equilibrium concentrations into the Ka expression, we get:```Ka = (1.00 x 10^-5.90 M)(0.025 M)/(0.075 M) = 4.2 x 10^-7```

Question 7

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. For calculating the volume of HCl required to reach a pH of 8.0, which of the following expressions is correct? (x = volume, in milliliters, of HCl required to reach a pH of 8.0)

Accepted Answer

The answer of Consider the titration of 100.0 mL of...

Question 8

A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein endpoint with 25.0 mL of 0.100 M NaOH. The student then adds 13.0 mL of 0.100 M HCl. The pH of the resulting solution is 4.7. Which of the following statements is true?

Accepted Answer

The answer of A student titrates an unknown weak acid,...

Question 9

A 100.0-mL sample of 0.2 M (CH₃)₃N (K_b = 5.3 * 10^-⁵) is titrated with 0.2 M HCl. What is the pH at the equivalence point?

Accepted Answer

At the equivalence point, the solution contains the conjugate acid of (CH₃)₃N, which is (CH₃)₃NH⁺. The pH is determined by the hydrolysis of this ion. Using the Kb of (CH₃)₃N, we can find the Ka of (CH₃)₃NH⁺ and calculate the pH, which is approximately 5.4.

Question 10

Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine, C₂H₅NH₂, by 1.0 M perchloric acid, HClO₄. (pK_b for C₂H₅NH₂ = 3.25)

Accepted Answer

The answer of Calculate the pH at the equivalence point...

Question 11

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 *10^-⁶, K_a2 = 1.0 *10^-¹⁰) is titrated with the following volumes of 1.00 M NaOH. 100.0 mL of 1.00 M NaOH

Accepted Answer

The answer of Calculate the pH when 200.0 mL of...

Question 12

An indicator HIn has K_a = 1 *10^-⁸. At pH = 6.0, what is the ratio HIn/In^-?

Accepted Answer

The pH is 6.0, and the pKa of the indicator is 8.0. Using the Henderson-Hasselbalch equation: pH = pKa + log([In-]/[HIn]), we find that log([In-]/[HIn]) = 6 - 8 = -2. Therefore, [In-]/[HIn] = 10^-2, which means [HIn]/[In-] = 100/1.

Question 13

A 200.0-mL sample of the weak acid HS1U1B13S1U1B0A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.)
-After 0 mL of 0.200 M NaOH is added

Accepted Answer

The answer of A 200.0-mL sample of the weak acid...

Question 14

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. Calculate the pH of the solution at the stoichiometric point.

Accepted Answer

The answer of Consider the titration of 100.0 mL of...

Question 15

A 100.-mL sample of 0.10 M HCl is mixed with 50. mL of 0.10 M NH₃. What is the resulting pH? (K_b for NH₃ = 1.8 *10^-⁵)

Accepted Answer

The HCl and NH3 react to form NH4Cl. The moles of HCl (0.01 mol) exceed the moles of NH3 (0.005 mol), leaving 0.005 mol of HCl unreacted in a total volume of 150 mL. The concentration of HCl is 0.033 M, leading to a pH of approximately 1.48.

Question 16

44.4 mL of a 1.42 M NaOH solution is titrated with a 1.90 M HCl solution. What is the final volume of the solution when the NaOH has been completely neutralized by the HCl? (Assume the volumes are additive.)

Accepted Answer

To find the final volume, first calculate the moles of NaOH: 44.4 mL * 1.42 M = 0.063048 moles. Since the reaction is 1:1, the same moles of HCl are needed: 0.063048 moles / 1.90 M = 0.0332 L = 33.2 mL. Add the volumes: 44.4 mL + 33.2 mL = 77.6 mL.

Question 17

A solution containing 10. mmol of CO₃²^- and 5.0 mmol of HCO₃^- is titrated with 1.0 M HCl. What volume of HCl must be added to reach the first equivalence point?

Accepted Answer

The first step is to write out the balanced chemical equation for the reaction between CO₃²^- and HCl: CO₃²^- + 2HCl -> ₃^- + H2O + CO2 From the equation, we can see that the stoichiometric ratio of CO₃²^- to HCl is 1:2. This means that to reach the first equivalence point, we will need to add enough HCl to react with all 10 mmol of CO₃²^-. The amount of HCl required can be calculated using the following formula: moles of HCl = (moles of CO₃²^-) x 2 moles of HCl = 10 mmol x 2 = 20 mmol Now we can use the definition of molarity (M) to calculate the volume of 1.0 M HCl required to provide 20 mmol of HCl: M = moles of solute / volume of solution rearranging, we get: volume of solution = moles of solute / M volume of solution = 20 mmol / 1.0 mol/L = 20 mL Therefore, the correct answer is C) 10 mL, as this is the volume of HCl required to reach the first equivalence point.

Question 18

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 11. Which of the following indicators would be best to use to mark the endpoint of this titration?

Accepted Answer

An indicator with K_a = 10^-12 has a pKa of 12, which is closest to the pH of 11 at the stoichiometric point, making it suitable for detecting the endpoint.

Question 19

Methyl orange is an indicator with a K_a of 1 * 10^-⁴. Its acid form, HIn, is red, while its base form, In^-, is yellow. At pH 6.0, the indicator will be

Accepted Answer

At pH 6.0, the pH is much higher than the pKa of methyl orange (pKa = 4), meaning the solution is basic relative to the pKa. Therefore, the indicator will be in its base form, which is yellow.

Question 20

Consider the following information about the diprotic acid ascorbic acid (HS1U1B12S1U1B0As for short, molar mass = 176.1).  The titration curve for disodium ascorbate, NaS1U1B12S1U1B0As, with standard HCl is shown below: 
-What major species is(are) present at point III?

Accepted Answer

At point III, the pH is around 4.5, which is the pKa1 of ascorbic acid. At this point, ascorbic acid is in its monoprotic form, H₂As, and the major species present are HAs^- and H₂As. Therefore, the best choice is E, which includes both of these species.

Quiz 8: Applications of Aqueous Equilibria

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 10. Which of the following indicator acids would be best to use to mark the endpoint of this titration?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 350.0 mL of 0.200 M NaOH is added

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below: -Which of the following is a major species present at point IV?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 200.0 mL of 0.200 M NaOH is added

A certain indicator HIn has a pK_a of 9.00, and a color change becomes visible when 7.00% of it is In^-. At what pH is this color change visible?

After adding 25.0 mL of 0.100 M NaOH to 100.0 mL of 0.100 M weak acid (HA) , the pH is found to be 5.90. Determine the value of K_a for the acid HA.

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. For calculating the volume of HCl required to reach a pH of 8.0, which of the following expressions is correct? (x = volume, in milliliters, of HCl required to reach a pH of 8.0)

A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein endpoint with 25.0 mL of 0.100 M NaOH. The student then adds 13.0 mL of 0.100 M HCl. The pH of the resulting solution is 4.7. Which of the following statements is true?

A 100.0-mL sample of 0.2 M (CH₃) ₃N (K_b = 5.3 * 10^-⁵) is titrated with 0.2 M HCl. What is the pH at the equivalence point?

Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine, C₂H₅NH₂, by 1.0 M perchloric acid, HClO₄. (pK_b for C₂H₅NH₂ = 3.25)

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 10^-⁶, K_a2 = 1.0 10^-¹⁰) is titrated with the following volumes of 1.00 M NaOH. 100.0 mL of 1.00 M NaOH

An indicator HIn has K_a = 1 *10^-⁸. At pH = 6.0, what is the ratio HIn/In^-?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 0 mL of 0.200 M NaOH is added

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. Calculate the pH of the solution at the stoichiometric point.

A 100.-mL sample of 0.10 M HCl is mixed with 50. mL of 0.10 M NH₃. What is the resulting pH? (K_b for NH₃ = 1.8 *10^-⁵)

44.4 mL of a 1.42 M NaOH solution is titrated with a 1.90 M HCl solution. What is the final volume of the solution when the NaOH has been completely neutralized by the HCl? (Assume the volumes are additive.)

A solution containing 10. mmol of CO₃²^- and 5.0 mmol of HCO₃^- is titrated with 1.0 M HCl. What volume of HCl must be added to reach the first equivalence point?

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 11. Which of the following indicators would be best to use to mark the endpoint of this titration?

Methyl orange is an indicator with a K_a of 1 * 10^-⁴. Its acid form, HIn, is red, while its base form, In^-, is yellow. At pH 6.0, the indicator will be

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below: -What major species is(are) present at point III?

Quiz 8: Applications of Aqueous Equilibria

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 10. Which of the following indicator acids would be best to use to mark the endpoint of this titration?

A 200.0-mL sample of the weak acid H3A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 350.0 mL of 0.200 M NaOH is added

Consider the following information about the diprotic acid ascorbic acid (H2As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na2As, with standard HCl is shown below: -Which of the following is a major species present at point IV?

A 200.0-mL sample of the weak acid H3A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 200.0 mL of 0.200 M NaOH is added

A certain indicator HIn has a pKa of 9.00, and a color change becomes visible when 7.00% of it is In-. At what pH is this color change visible?

After adding 25.0 mL of 0.100 M NaOH to 100.0 mL of 0.100 M weak acid (HA) , the pH is found to be 5.90. Determine the value of Ka for the acid HA.

Consider the titration of 100.0 mL of 0.250 M aniline (Kb = 3.8 *10-10) with 0.500 M HCl. For calculating the volume of HCl required to reach a pH of 8.0, which of the following expressions is correct? (x = volume, in milliliters, of HCl required to reach a pH of 8.0)

A student titrates an unknown weak acid, HA, to a pale pink phenolphthalein endpoint with 25.0 mL of 0.100 M NaOH. The student then adds 13.0 mL of 0.100 M HCl. The pH of the resulting solution is 4.7. Which of the following statements is true?

A 100.0-mL sample of 0.2 M (CH3) 3N (Kb = 5.3 * 10-5) is titrated with 0.2 M HCl. What is the pH at the equivalence point?

Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine, C2H5NH2, by 1.0 M perchloric acid, HClO4. (pKb for C2H5NH2 = 3.25)

Calculate the pH when 200.0 mL of a 1.00 M solution of H2A (Ka1 = 1.0 *10-6, Ka2 = 1.0 *10-10) is titrated with the following volumes of 1.00 M NaOH. 100.0 mL of 1.00 M NaOH

An indicator HIn has Ka = 1 *10-8. At pH = 6.0, what is the ratio HIn/In-?

A 200.0-mL sample of the weak acid H3A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 0 mL of 0.200 M NaOH is added

Consider the titration of 100.0 mL of 0.250 M aniline (Kb = 3.8 *10-10) with 0.500 M HCl. Calculate the pH of the solution at the stoichiometric point.

A 100.-mL sample of 0.10 M HCl is mixed with 50. mL of 0.10 M NH3. What is the resulting pH? (Kb for NH3 = 1.8 *10-5)

44.4 mL of a 1.42 M NaOH solution is titrated with a 1.90 M HCl solution. What is the final volume of the solution when the NaOH has been completely neutralized by the HCl? (Assume the volumes are additive.)

A solution containing 10. mmol of CO32- and 5.0 mmol of HCO3- is titrated with 1.0 M HCl. What volume of HCl must be added to reach the first equivalence point?

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 11. Which of the following indicators would be best to use to mark the endpoint of this titration?

Methyl orange is an indicator with a Ka of 1 * 10-4. Its acid form, HIn, is red, while its base form, In-, is yellow. At pH 6.0, the indicator will be

Consider the following information about the diprotic acid ascorbic acid (H2As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na2As, with standard HCl is shown below: -What major species is(are) present at point III?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 350.0 mL of 0.200 M NaOH is added

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below: -Which of the following is a major species present at point IV?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 200.0 mL of 0.200 M NaOH is added

A certain indicator HIn has a pK_a of 9.00, and a color change becomes visible when 7.00% of it is In^-. At what pH is this color change visible?

After adding 25.0 mL of 0.100 M NaOH to 100.0 mL of 0.100 M weak acid (HA) , the pH is found to be 5.90. Determine the value of K_a for the acid HA.

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. For calculating the volume of HCl required to reach a pH of 8.0, which of the following expressions is correct? (x = volume, in milliliters, of HCl required to reach a pH of 8.0)

A 100.0-mL sample of 0.2 M (CH₃) ₃N (K_b = 5.3 * 10^-⁵) is titrated with 0.2 M HCl. What is the pH at the equivalence point?

Calculate the pH at the equivalence point for the titration of 1.0 M ethylamine, C₂H₅NH₂, by 1.0 M perchloric acid, HClO₄. (pK_b for C₂H₅NH₂ = 3.25)

Calculate the pH when 200.0 mL of a 1.00 M solution of H₂A (K_a1 = 1.0 10^-⁶, K_a2 = 1.0 10^-¹⁰) is titrated with the following volumes of 1.00 M NaOH. 100.0 mL of 1.00 M NaOH

An indicator HIn has K_a = 1 *10^-⁸. At pH = 6.0, what is the ratio HIn/In^-?

A 200.0-mL sample of the weak acid H₃A (0.100 M) is titrated with 0.200 M NaOH. What are the major species at each of the following points in the titration? (Water is always assumed to be a major species.) -After 0 mL of 0.200 M NaOH is added

Consider the titration of 100.0 mL of 0.250 M aniline (K_b = 3.8 *10^-¹⁰) with 0.500 M HCl. Calculate the pH of the solution at the stoichiometric point.

A 100.-mL sample of 0.10 M HCl is mixed with 50. mL of 0.10 M NH₃. What is the resulting pH? (K_b for NH₃ = 1.8 *10^-⁵)

A solution containing 10. mmol of CO₃²^- and 5.0 mmol of HCO₃^- is titrated with 1.0 M HCl. What volume of HCl must be added to reach the first equivalence point?

Methyl orange is an indicator with a K_a of 1 * 10^-⁴. Its acid form, HIn, is red, while its base form, In^-, is yellow. At pH 6.0, the indicator will be

Consider the following information about the diprotic acid ascorbic acid (H₂As for short, molar mass = 176.1) . The titration curve for disodium ascorbate, Na₂As, with standard HCl is shown below: -What major species is(are) present at point III?