Question 1

A solution is prepared by mixing 500. mL of 0.10 M NaOCl and 500. mL of 0.20 M HOCl. What is the pH of this solution? [K_a(HOCl)= 3.2 * 10^-8]

Accepted Answer

HOCl is a weak acid and NaOCl is its conjugate base. From the given values, we can see that HOCl is present in excess, so we can assume it as the limiting reagent.

Step 1: Write the balanced equation for the reaction between NaOCl and HOCl:
NaOCl + HOCl → NaCl + HOClO

Step 2: Calculate the moles of HOCl present in the solution:
0.20 M HOCl × 0.5 L = 0.10 moles HOCl

Step 3: Calculate the moles of NaOCl that react with the above amount of HOCl:
0.10 moles HOCl × (1 mole NaOCl/1 mole HOCl) = 0.10 moles NaOCl

Step 4: Calculate the final volume of the solution:
500 mL + 500 mL = 1000 mL = 1 L

Step 5: Calculate the molarity of the final solution:
Molarity = Total moles of solute/Total volume of solution
Molarity = (0.10 moles HOCl + 0.10 moles NaOCl)/1 L = 0.20 M

Step 6: Calculate the pKa value of HOCl:
pKa = -log(Ka) = -log(1.2 × 10^-8) = 7.92

Step 7: Use the Henderson-Hasselbalch equation to calculate the pH of the solution:
pH = pKa + log([A-]/[HA])
where [A-] is the concentration of NaOCl (conjugate base) and [HA] is the concentration of HOCl (acid)

[A-]/[HA] = (0.10 M)/(0.20 M) = 0.5
pH = 7.92 + log(0.5) = 7.19

Therefore, the pH of the solution is 7.19, which is closest to choice C.

Question 2

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 4.6-4.8?

Accepted Answer

The appropriate buffer pH range is between 4.6 and 4.8, indicating that the buffer's pKa value should be 4.7. The pKa of acetic acid, CH3COOH, which is similar to the structure of the acid in option A, is approximately 4.76. Thus, option A comprises a suitable acid, and its conjugate base has comparable concentration to form a buffer solution. Options B, C, D, and E are not suitable because their pKa values vary beyond the desired range.

Question 3

Calculate the percent ionization of cyanic acid, K_a = 2.0 * 10^-4, in a buffer solution that is 0.50 M HCNO and 0.10 M NaCNO.

Accepted Answer

C

Question 4

You have 500.0 mL of a buffer solution containing 0.30 M acetic acid (CH₃COOH)and 0.20 M sodium acetate (CH₃COONa). What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

Accepted Answer

To approach this problem, we need to use the Henderson-Hasselbalch equation:

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

where pKa is the dissociation constant of acetic acid, [base] is the concentration of sodium acetate, and [acid] is the concentration of acetic acid.

The pKa of acetic acid is 4.76. Therefore,

pH = 4.76 + log([0.20]/[0.30]) = 4.71

Now we add 20.0 mL of 1.00 M NaOH to the solution. The reaction that occurs is:

CH3COOH + OH- → CH3COO- + H2O

We can use the stoichiometry of the balanced equation to calculate the new concentrations of acetic acid and acetate ion.

Initially, we had 0.3 M of acetic acid and 0.2 M of sodium acetate. This corresponds to:

[CH3COOH] = 0.3 M 
[CH3COO-] = 0.2 M

After the addition of NaOH, the amount of acetic acid that reacts will be equal to the amount of NaOH added. This can be calculated using the concentration and volume of NaOH added:

moles of NaOH added = 1.00 M x 0.0200 L = 0.0200 mol NaOH

Since the reaction is 1:1, this means that 0.0200 mol of acetic acid reacts. We can then subtract this from our initial value to get the new concentration of acetic acid:

[CH3COOH] = (0.3 mol - 0.0200 mol) / 0.520 L = 0.535 M

Similarly, the reaction will also produce an equivalent amount of acetate ion:

[CH3COO-] = (0.2 mol + 0.0200 mol) / 0.520 L = 0.423 M

We can now use the Henderson-Hasselbalch equation again to calculate the new pH:

pH = 4.76 + log(0.423/0.535) = 4.71

This is the same as the initial pH, which means that the solution is a good buffer and able to resist changes in pH upon addition of small amounts of acid or base. Therefore, the answer is B.

Question 5

You are asked to go into the lab and prepare an acetic acid - sodium acetate buffer solution with a pH of 4.00 ± 0.02. What molar ratio of CH₃COOH to CH₃COONa should be used?

Accepted Answer

The answer of You are asked to go into the...

Question 6

A titration of an acid and base to the equivalence point results in a noticeably acidic solution. It is likely this titration involves

Accepted Answer

When a strong acid is titrated with a weak base, the resulting solution at the equivalence point is acidic due to the weak base not being able to fully neutralize the strong acid.

Question 7

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO)and 0.80 mole of sodium cyanate (NaCNO)in enough water to make 1.0 liter of solution. [K_a(HCNO)= 2.0 * 10^-4]

Accepted Answer

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

Question 8

Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C₆H₅CO₂H)and 0.15M sodium benzoate (C₆H₅COONa). [K_a = 6.5 * 10^-5 for benzoic acid]

Accepted Answer

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

Question 9

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 9.2-9.3?

Accepted Answer

The answer of Assuming equal concentrations of conjugate base and...

Question 10

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of sodium cyanate (NaCNO)and 1.0 mole of cyanic acid (HCNO)in enough water to make 1.0 liter of solution. [K_a(HCNO)= 2.0 * 10^-4]

Accepted Answer

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

Question 11

What is the net ionic equation for the reaction that occurs when small amounts of hydrochloric acid are added to a HOCl/NaOCl buffer solution?

Accepted Answer

The correct net ionic equation for the reaction when HCl is added to a HOCl/NaOCl buffer solution is $H^+ + OCl^- \rightarrow HOCl$. This equation shows the reaction of the hydrogen ion (from HCl) with the hypochlorite ion (from NaOCl) to form hypochlorous acid (HOCl), which is consistent with how a buffer works to neutralize added acid.

Question 12

Over what range of pH is a HOCl - NaOCl buffer effective?

Accepted Answer

HOCl - NaOCl buffer is effective in the pH range of 6.5 to 8.5, which is within the physiological pH range. Outside this range, the buffer is not effective as the pH is too acidic or too basic for the buffer to maintain its pH stability. Therefore, options A, B, D, and E can be ruled out.

Question 13

You have 500.0 mL of a buffer solution containing 0.20 M acetic acid (CH₃COOH)and 0.30 M sodium acetate (CH₃COONa). What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

Accepted Answer

The answer of You have 500.0 mL of a buffer...

Question 14

Which one of the following combinations cannot function as a buffer solution?

Accepted Answer

A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid. HNO3 (nitric acid) is a strong acid, and NaNO3 is its salt. Since HNO3 fully dissociates in water, it cannot form a buffer solution with its salt.

Question 15

Which one of the following is a buffer solution?

Accepted Answer

A buffer solution consists of a weak acid and its conjugate base or a weak base and its conjugate acid. Option A contains the weak acid HCN and its conjugate base KCN in appropriate concentrations, which makes it a buffer solution. Option B is just one compound and not a weak acid-base pair. Option C contains a strong base and its conjugate acid, which is not a buffer solution. Option D contains just the conjugate base and not the weak acid. Option E contains a strong acid and its conjugate base, which is not a buffer solution.

Question 16

Calculate the pH of a solution that is 0.410 M in HOCl and 0.050 M in NaOCl. [K_a(HOCl)= 3.2 * 10^-8]

Accepted Answer

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

Question 17

Acid dissociation constants for phosphoric acid are given below.  A buffer with a pH = 7.4 can best be made by using

Accepted Answer

To make a buffer with pH = 7.4, we need to choose a weak acid (conjugate acid of a weak base) and its salt with a strong base. From the given choices, only option B has a weak acid and its salt with a strong base. NaHSO4 is the salt of weak acid H2SO4 and strong base NaOH. NaH2PO4 is the salt of weak acid H2PO4- and strong base NaOH. So, option B with NaHSO4 and NaH2PO4 would make the best buffer with pH = 7.4.

Question 18

Consider a buffer solution prepared from HOCl and NaOCl. Which is the net ionic equation for the reaction that occurs when NaOH is added to this buffer?

Accepted Answer

The answer of Consider a buffer solution prepared from HOCl...

Question 19

The pH at the equivalence point of a titration may differ from 7.0 due to

Accepted Answer

The pH at the equivalence point can differ from 7.0 due to the hydrolysis of the salt formed. This occurs when the salt produced in the reaction contains a cation or anion that can react with water to form an acidic or basic solution, respectively. This can shift the pH away from 7.0, which is the pH of a neutral solution.

Question 20

For which type of titration will the pH be basic at the equivalence point?

Accepted Answer

In a weak acid vs. strong base titration, the equivalence point occurs when all of the acid has been neutralized by the strong base. At this point, the pH will be basic because the excess of hydroxide ions from the strong base will make the solution more basic. In strong acid vs. strong base titration, the equivalence point occurs when the moles of acid are equal to the moles of base, resulting in a neutral pH. In strong acid vs. weak base titration, the equivalence point occurs when the pH is less than 7, indicating that the solution is acidic.

Quiz 17: Acid-Base Equilibria and Solubility Equilibria

A solution is prepared by mixing 500. mL of 0.10 M NaOCl and 500. mL of 0.20 M HOCl. What is the pH of this solution? [K_a(HOCl) = 3.2 * 10^-8]

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 4.6-4.8?

Calculate the percent ionization of cyanic acid, K_a = 2.0 * 10^-4, in a buffer solution that is 0.50 M HCNO and 0.10 M NaCNO.

You have 500.0 mL of a buffer solution containing 0.30 M acetic acid (CH₃COOH) and 0.20 M sodium acetate (CH₃COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

You are asked to go into the lab and prepare an acetic acid - sodium acetate buffer solution with a pH of 4.00 ± 0.02. What molar ratio of CH₃COOH to CH₃COONa should be used?

A titration of an acid and base to the equivalence point results in a noticeably acidic solution. It is likely this titration involves

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution. [K_a(HCNO) = 2.0 * 10^-4]

Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C₆H₅CO₂H) and 0.15M sodium benzoate (C₆H₅COONa) . [K_a = 6.5 * 10^-5 for benzoic acid]

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 9.2-9.3?

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of sodium cyanate (NaCNO) and 1.0 mole of cyanic acid (HCNO) in enough water to make 1.0 liter of solution. [K_a(HCNO) = 2.0 * 10^-4]

What is the net ionic equation for the reaction that occurs when small amounts of hydrochloric acid are added to a HOCl/NaOCl buffer solution?

Over what range of pH is a HOCl - NaOCl buffer effective?

You have 500.0 mL of a buffer solution containing 0.20 M acetic acid (CH₃COOH) and 0.30 M sodium acetate (CH₃COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

Which one of the following combinations cannot function as a buffer solution?

Which one of the following is a buffer solution?

Calculate the pH of a solution that is 0.410 M in HOCl and 0.050 M in NaOCl. [K_a(HOCl) = 3.2 * 10^-8]

Acid dissociation constants for phosphoric acid are given below. A buffer with a pH = 7.4 can best be made by using

Consider a buffer solution prepared from HOCl and NaOCl. Which is the net ionic equation for the reaction that occurs when NaOH is added to this buffer?

The pH at the equivalence point of a titration may differ from 7.0 due to

For which type of titration will the pH be basic at the equivalence point?

Quiz 17: Acid-Base Equilibria and Solubility Equilibria

A solution is prepared by mixing 500. mL of 0.10 M NaOCl and 500. mL of 0.20 M HOCl. What is the pH of this solution? [Ka(HOCl) = 3.2 * 10-8]

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 4.6-4.8?

Calculate the percent ionization of cyanic acid, Ka = 2.0 * 10-4, in a buffer solution that is 0.50 M HCNO and 0.10 M NaCNO.

You have 500.0 mL of a buffer solution containing 0.30 M acetic acid (CH3COOH) and 0.20 M sodium acetate (CH3COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [Ka = 1.8 * 10-5]

You are asked to go into the lab and prepare an acetic acid - sodium acetate buffer solution with a pH of 4.00 ± 0.02. What molar ratio of CH3COOH to CH3COONa should be used?

A titration of an acid and base to the equivalence point results in a noticeably acidic solution. It is likely this titration involves

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution. [Ka(HCNO) = 2.0 * 10-4]

Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C6H5CO2H) and 0.15M sodium benzoate (C6H5COONa) . [Ka = 6.5 * 10-5 for benzoic acid]

Assuming equal concentrations of conjugate base and acid, which one of the following mixtures is suitable for making a buffer solution with an optimum pH of 9.2-9.3?

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of sodium cyanate (NaCNO) and 1.0 mole of cyanic acid (HCNO) in enough water to make 1.0 liter of solution. [Ka(HCNO) = 2.0 * 10-4]

What is the net ionic equation for the reaction that occurs when small amounts of hydrochloric acid are added to a HOCl/NaOCl buffer solution?

Over what range of pH is a HOCl - NaOCl buffer effective?

You have 500.0 mL of a buffer solution containing 0.20 M acetic acid (CH3COOH) and 0.30 M sodium acetate (CH3COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [Ka = 1.8 * 10-5]

Which one of the following combinations cannot function as a buffer solution?

Which one of the following is a buffer solution?

Calculate the pH of a solution that is 0.410 M in HOCl and 0.050 M in NaOCl. [Ka(HOCl) = 3.2 * 10-8]

Acid dissociation constants for phosphoric acid are given below. A buffer with a pH = 7.4 can best be made by using

Consider a buffer solution prepared from HOCl and NaOCl. Which is the net ionic equation for the reaction that occurs when NaOH is added to this buffer?

The pH at the equivalence point of a titration may differ from 7.0 due to

For which type of titration will the pH be basic at the equivalence point?

A solution is prepared by mixing 500. mL of 0.10 M NaOCl and 500. mL of 0.20 M HOCl. What is the pH of this solution? [K_a(HOCl) = 3.2 * 10^-8]

Calculate the percent ionization of cyanic acid, K_a = 2.0 * 10^-4, in a buffer solution that is 0.50 M HCNO and 0.10 M NaCNO.

You have 500.0 mL of a buffer solution containing 0.30 M acetic acid (CH₃COOH) and 0.20 M sodium acetate (CH₃COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

You are asked to go into the lab and prepare an acetic acid - sodium acetate buffer solution with a pH of 4.00 ± 0.02. What molar ratio of CH₃COOH to CH₃COONa should be used?

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of cyanic acid (HCNO) and 0.80 mole of sodium cyanate (NaCNO) in enough water to make 1.0 liter of solution. [K_a(HCNO) = 2.0 * 10^-4]

Calculate the pH of a buffer solution that contains 0.25 M benzoic acid (C₆H₅CO₂H) and 0.15M sodium benzoate (C₆H₅COONa) . [K_a = 6.5 * 10^-5 for benzoic acid]

Calculate the pH of a buffer solution prepared by dissolving 0.20 mole of sodium cyanate (NaCNO) and 1.0 mole of cyanic acid (HCNO) in enough water to make 1.0 liter of solution. [K_a(HCNO) = 2.0 * 10^-4]

You have 500.0 mL of a buffer solution containing 0.20 M acetic acid (CH₃COOH) and 0.30 M sodium acetate (CH₃COONa) . What will the pH of this solution be after the addition of 20.0 mL of 1.00 M NaOH solution? [K_a = 1.8 * 10^-5]

Calculate the pH of a solution that is 0.410 M in HOCl and 0.050 M in NaOCl. [K_a(HOCl) = 3.2 * 10^-8]