Question 1

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of HCl is added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

Accepted Answer

When 2.0 mmol of HCl is added to the buffer, it reacts with the sodium acetate, converting it to acetic acid. This decreases the concentration of acetate ions and increases the concentration of acetic acid. The change in concentrations can be calculated as follows: the initial moles of acetic acid and acetate are both 0.0200 mol (since the volume is 1.00 L and their concentrations are 0.0200 M). After the addition of 2.0 mmol (or 0.0020 mol) of HCl, the moles of acetate decrease by 0.0020 mol, and the moles of acetic acid increase by 0.0020 mol. Therefore, the new concentrations are 0.0220 M for acetic acid and 0.0180 M for acetate.The pH of the buffer solution can be calculated using the Henderson-Hasselbalch equation:$$ \text{pH} = \text{p}K_a + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right) $$$$ \text{pH} = 4.75 + \log\left(\frac{0.0180}{0.0220}\right) $$$$ \text{pH} = 4.75 + \log(0.8182) $$$$ \text{pH} = 4.75 - 0.087 $$$$ \text{pH} = 4.663 $$Rounding to two decimal places, the pH is approximately 4.66.

Question 2

For pyridine,pK_b = 8.75.What is the pH of an aqueous buffer solution that is 0.300 M C₅H₅N(aq)and 0.500 M C₅H₅NHCl(aq)?

Accepted Answer

The answer of For pyridine,pK_b = 8.75.What is the pH...

Question 3

The following compounds are available as 0.10 M aqueous solutions.  Which two solutions could be used to prepare a buffer with a pH of ~ 9? More than one answer may be possible.

Accepted Answer

The answer of The following compounds are available as 0.10...

Question 4

Calculate the ratio of the molarities of HPO₄^2- and H₂PO₄^- ions required to achieve buffering at pH = 7.00.For H₃PO₄,pK_a1 = 2.12,pK_a2 = 7.21,and pK_a3 = 12.68.

Accepted Answer

We can use the Henderson-Hasselbalch equation to calculate the ratio of the molarities:

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

At pH 7.00, we can use the third pKa value (12.68) to calculate the ratio:

7.00 = 12.68 + log([A-]/[HA])
-5.68 = log([A-]/[HA])
10^-5.68 = [A-]/[HA]

Now we need to determine which ions correspond to A- and HA. We know that HS1U1B13S1U1B0 will donate a proton and become HS1U1B12S1U1B0, which is HA. Therefore, POS1U1B14S1U1B0F1F1F1S1S1U1P1- is A-.

Now we can calculate the ratio:

[A-]/[HA] = ([POS1U1B14S1U1B0F1F1F1S1S1U1P1-]/[HS1U1B12S1U1B0])
= (10^-7.21)/(10^-2.12)
= 10^-5.09

This is equivalent to 0.62, which is closest to choice C.

Question 5

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of NaOH are added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

Accepted Answer

The answer of A buffer solution contains 0.0200 M acetic...

Question 6

The following compounds are available as 0.10 M aqueous solutions.  Which two solutions could be used to prepare a buffer with a pH of ~ 2.5?

Accepted Answer

The answer of The following compounds are available as 0.10...

Question 7

A buffer solution contains 0.25 M NaNO₂(aq)and 0.80 M HNO₂(aq)(pK_a = 3.37).What is the pH after 0.10 mol HBr are added to 1.00 L of this buffer?

Accepted Answer

First, we must determine which species, the acid or the base, will react with the added HBr. HBr is a strong acid, so it will protonate the weak base, NaNO₂, to form HNO₂ and NaBr: HBr + NaNO₂ → HNO₂ + NaBr Since the buffer contains a higher concentration of HNO₂ than NaNO₂, the added HBr will react primarily with NaNO₂ until it is depleted. We can then use the Henderson-Hasselbalch equation to calculate the pH of the buffer after the addition of HBr: pH = pKa + log([A-]/[HA]) where pKa is the dissociation constant of the weak acid (HNO₂), [HA] is the concentration of the weak acid (HNO₂), and [A-] is the concentration of the conjugate base (NaNO₂) after it has reacted with the added HBr. First, we must determine how much of the NaNO₂ will react with the added HBr. Since the buffer contains 0.25 M NaNO₂ and 0.10 mol (0.10 M) HBr is added, the concentration of NaNO₂ remaining after the reaction will be: 0.25 M - 0.10 M = 0.15 M Now, we can calculate the concentration of the conjugate base, [A-], after the reaction: [A-] = moles of NaNO₂ remaining / total volume moles of NaNO₂ remaining = 0.15 M * 1.00 L = 0.15 mol total volume = 1.00 L + volume of 0.10 M HBr added Since we added 0.10 mol of HBr to 1.00 L of the buffer, the total volume is 1.10 L. [A-] = 0.15 mol / 1.10 L = 0.136 M Plugging in the values to the Henderson-Hasselbalch equation: pH = 3.37 + log(0.136/0.80) = 2.59 Therefore, the pH of the buffer after the addition of 0.10 mol HBr is 2.59.

Question 8

A buffer contains equal concentrations of NH₃(aq)and NH₄Cl(aq).What is the pH of the buffer? (K_b (NH₃)= 1.8 * 10^-5)

Accepted Answer

The pH of the buffer can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). Given that the concentrations of NH3 and NH4Cl are equal, the log([A-]/[HA]) term equals 0. Thus, pH = pKa. The pKa of NH4+ (given as the Kb of NH3 = 1.8 * 10^-5) can be found by using the relation pKa + pKb = 14. The pKb of NH3 is -log(1.8 * 10^-5) = 4.74, so pKa = 14 - 4.74 = 9.26.

Question 9

The following compounds are available as 0.10 M aqueous solutions.  Which two solutions could be used to prepare a buffer with a pH of ~ 7?

Accepted Answer

The answer of The following compounds are available as 0.10...

Question 10

For NH₃,pK_b = 4.74.What is the pH of an aqueous buffer solution that is 0.050 M NH₃(aq)and 0.20 M NH₄Cl(aq)?

Accepted Answer

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation: pH = pKa + log([base]/[acid]). First, calculate pKa from pKb: pKa = 14 - pKb = 14 - 4.74 = 9.26. Then, apply the equation: pH = 9.26 + log(0.050/0.20) = 9.26 + log(0.25) = 9.26 - 0.60 = 8.66.

Question 11

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid,K_a = 1.8 * 10^-5 and for NH₃,K_b = 1.8 * 10^-5.

Accepted Answer

To form a buffer solution with pH less than 7, we need a weak acid and its conjugate base in nearly equal amounts. Option B gives us acetic acid (weak acid) and NaOH (strong base) which will form the conjugate base, acetate ion. The addition of NaOH will result in a higher concentration of the conjugate base, which will help maintain the pH of the solution near its pKa value (4.76 for acetic acid). The other options either do not contain a weak acid or do not have components in nearly equal amounts.

Question 12

A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄.What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^- is 7.21.

Accepted Answer

The addition of KOH will react with H2PO4- to form HPO4^2- and water. Since 0.10 mol of KOH is added, the concentration of H2PO4- will decrease by 0.10 mol and the concentration of HPO4^2- will increase by 0.10 mol. This results in 0.65 mol of H2PO4- and 0.85 mol of HPO4^2- in the solution. Using the Henderson-Hasselbalch equation, pH = pKa + log([base]/[acid]) = 7.21 + log(0.85/0.65) = 7.33.

Question 13

Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO,K_a = 2.2 * 10^-4 and for NH₃,K_b = 1.8 * 10F1F1F1S1^-5.

Accepted Answer

The answer of Which of the following mixtures gives a...

Question 14

The following compounds are available as 0.10 M aqueous solutions.  Pick two solutions that could be used to prepare a buffer with a pH of ~ 4.

Accepted Answer

The answer of The following compounds are available as 0.10...

Question 15

If a small amount of a strong acid is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

Accepted Answer

The strong acid reacts with A^- to give HA, which is a weak acid. This will not change the pH of the buffer solution appreciably because the buffer will resist changes in pH.

Question 16

A buffer contains equal concentrations of a weak acid,HA,and its conjugate base,A^-.If the value of K_a for HA is 1.0 * 10^-9,what is the pH of the buffer?

Accepted Answer

The answer of A buffer contains equal concentrations of a...

Question 17

If a small amount of a strong base is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

Accepted Answer

The strong base reacts with the weak acid (HA) in the buffer to form its conjugate base (A⁻), which helps maintain the pH by neutralizing the added base.

Question 18

Calculate the ratio of the molarities of CO₃²^- and HCO₃^- ions required to achieve buffering at pH = 9.0.For H₂CO₃,pK_a1 = 6.37,and pK_a2 = 10.00.

Accepted Answer

The Henderson-Hasselbalch equation for the bicarbonate buffer system is used: pH = pKa2 + log([CO3^2-]/[HCO3^-]). Substituting the given values, 9.0 = 10.00 + log([CO3^2-]/[HCO3^-]), solving gives [CO3^2-]/[HCO3^-] = 0.32.

Question 19

For HF,pK_a = 3.45.What is the pH of an aqueous buffer solution that is 0.100 M HF(aq)and 0.300 M KF(aq)?

Accepted Answer

The dissociation of HF in water can be represented by the equation: HF(aq) + H2O(l) ⇌ H3O+(aq) + F-(aq) The equilibrium expression for this reaction is: Ka = [H3O+][F-]/[HF] We know that pK_a = 3.45, which means that: pKa = -log(Ka) = -log([H3O+][F-]/[HF]) = 3.45 Therefore, we can solve for [H3O+] using the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]) pH = 3.45 + log([KF]/[HF]) pH = 3.45 + log(0.300/0.100) = 3.93 Therefore, the pH of the buffer solution is 3.93, which is closest to option D (3.93).

Question 20

The following compounds are available as 0.10 M aqueous solutions.  Pick two solutions that could be used to prepare a buffer with a pH of ~ 10.8.More than one answer may be possible.

Accepted Answer

The answer of The following compounds are available as 0.10...

Quiz 13: Aqueous Equilibria

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of HCl is added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

For pyridine,pK_b = 8.75.What is the pH of an aqueous buffer solution that is 0.300 M C₅H₅N(aq) and 0.500 M C₅H₅NHCl(aq) ?

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 9? More than one answer may be possible.

Calculate the ratio of the molarities of HPO₄^2- and H₂PO₄^- ions required to achieve buffering at pH = 7.00.For H₃PO₄,pK_a1 = 2.12,pK_a2 = 7.21,and pK_a3 = 12.68.

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of NaOH are added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 2.5?

A buffer solution contains 0.25 M NaNO₂(aq) and 0.80 M HNO₂(aq) (pK_a = 3.37) .What is the pH after 0.10 mol HBr are added to 1.00 L of this buffer?

A buffer contains equal concentrations of NH₃(aq) and NH₄Cl(aq) .What is the pH of the buffer? (K_b (NH₃) = 1.8 * 10^-5)

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 7?

For NH₃,pK_b = 4.74.What is the pH of an aqueous buffer solution that is 0.050 M NH₃(aq) and 0.20 M NH₄Cl(aq) ?

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid,K_a = 1.8 * 10^-5 and for NH₃,K_b = 1.8 * 10^-5.

A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄.What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^- is 7.21.

Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO,K_a = 2.2 * 10^-4 and for NH₃,K_b = 1.8 * 10^-5.

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 4.

If a small amount of a strong acid is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

A buffer contains equal concentrations of a weak acid,HA,and its conjugate base,A^-.If the value of K_a for HA is 1.0 * 10^-9,what is the pH of the buffer?

If a small amount of a strong base is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

Calculate the ratio of the molarities of CO₃²^- and HCO₃^- ions required to achieve buffering at pH = 9.0.For H₂CO₃,pK_a1 = 6.37,and pK_a2 = 10.00.

For HF,pK_a = 3.45.What is the pH of an aqueous buffer solution that is 0.100 M HF(aq) and 0.300 M KF(aq) ?

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 10.8.More than one answer may be possible.

Quiz 13: Aqueous Equilibria

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of HCl is added to 1.00 L of this buffer? pKa = 4.75 for acetic acid.

For pyridine,pKb = 8.75.What is the pH of an aqueous buffer solution that is 0.300 M C5H5N(aq) and 0.500 M C5H5NHCl(aq) ?

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 9? More than one answer may be possible.

Calculate the ratio of the molarities of HPO42- and H2PO4- ions required to achieve buffering at pH = 7.00.For H3PO4,pKa1 = 2.12,pKa2 = 7.21,and pKa3 = 12.68.

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of NaOH are added to 1.00 L of this buffer? pKa = 4.75 for acetic acid.

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 2.5?

A buffer solution contains 0.25 M NaNO2(aq) and 0.80 M HNO2(aq) (pKa = 3.37) .What is the pH after 0.10 mol HBr are added to 1.00 L of this buffer?

A buffer contains equal concentrations of NH3(aq) and NH4Cl(aq) .What is the pH of the buffer? (Kb (NH3) = 1.8 * 10-5)

The following compounds are available as 0.10 M aqueous solutions. Which two solutions could be used to prepare a buffer with a pH of ~ 7?

For NH3,pKb = 4.74.What is the pH of an aqueous buffer solution that is 0.050 M NH3(aq) and 0.20 M NH4Cl(aq) ?

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid,Ka = 1.8 * 10-5 and for NH3,Kb = 1.8 * 10-5.

A buffer solution contains 0.75 mol KH2PO4 and 0.75 mol K2HPO4.What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pKa of H2PO4- is 7.21.

Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO,Ka = 2.2 * 10-4 and for NH3,Kb = 1.8 * 10-5.

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 4.

If a small amount of a strong acid is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

A buffer contains equal concentrations of a weak acid,HA,and its conjugate base,A-.If the value of Ka for HA is 1.0 * 10-9,what is the pH of the buffer?

If a small amount of a strong base is added to buffer made up of a weak acid,HA,and the sodium salt of its conjugate base,NaA,the pH of the buffer solution does not change appreciably because

Calculate the ratio of the molarities of CO32- and HCO3- ions required to achieve buffering at pH = 9.0.For H2CO3,pKa1 = 6.37,and pKa2 = 10.00.

For HF,pKa = 3.45.What is the pH of an aqueous buffer solution that is 0.100 M HF(aq) and 0.300 M KF(aq) ?

The following compounds are available as 0.10 M aqueous solutions. Pick two solutions that could be used to prepare a buffer with a pH of ~ 10.8.More than one answer may be possible.

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of HCl is added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

For pyridine,pK_b = 8.75.What is the pH of an aqueous buffer solution that is 0.300 M C₅H₅N(aq) and 0.500 M C₅H₅NHCl(aq) ?

Calculate the ratio of the molarities of HPO₄^2- and H₂PO₄^- ions required to achieve buffering at pH = 7.00.For H₃PO₄,pK_a1 = 2.12,pK_a2 = 7.21,and pK_a3 = 12.68.

A buffer solution contains 0.0200 M acetic acid and 0.0200 M sodium acetate.What is the pH after 2.0 mmol of NaOH are added to 1.00 L of this buffer? pK_a = 4.75 for acetic acid.

A buffer solution contains 0.25 M NaNO₂(aq) and 0.80 M HNO₂(aq) (pK_a = 3.37) .What is the pH after 0.10 mol HBr are added to 1.00 L of this buffer?

A buffer contains equal concentrations of NH₃(aq) and NH₄Cl(aq) .What is the pH of the buffer? (K_b (NH₃) = 1.8 * 10^-5)

For NH₃,pK_b = 4.74.What is the pH of an aqueous buffer solution that is 0.050 M NH₃(aq) and 0.20 M NH₄Cl(aq) ?

Which of the following mixtures gives a buffer with a pH less than 7.0? For acetic acid,K_a = 1.8 * 10^-5 and for NH₃,K_b = 1.8 * 10^-5.

A buffer solution contains 0.75 mol KH₂PO₄ and 0.75 mol K₂HPO₄.What is the pH after 0.10 mol KOH is added to 1.00 L of this buffer? The pK_a of H₂PO₄^- is 7.21.

Which of the following mixtures gives a buffer with a pH greater than 7.0? For HCNO,K_a = 2.2 * 10^-4 and for NH₃,K_b = 1.8 * 10^-5.

A buffer contains equal concentrations of a weak acid,HA,and its conjugate base,A^-.If the value of K_a for HA is 1.0 * 10^-9,what is the pH of the buffer?

Calculate the ratio of the molarities of CO₃²^- and HCO₃^- ions required to achieve buffering at pH = 9.0.For H₂CO₃,pK_a1 = 6.37,and pK_a2 = 10.00.

For HF,pK_a = 3.45.What is the pH of an aqueous buffer solution that is 0.100 M HF(aq) and 0.300 M KF(aq) ?