Question 1

The following compounds are available as 0.10 M aqueous solutions. $$\begin{array} { | l | l | l | } 
\hline \text { A) pyridine } & \text { B) } \mathrm { LiClO } _ { 4 } & \text { C) } \mathrm { HClO } _ { 4 } \
\hline \text { D) } \mathrm { HClO } _ { 2 } & \text { E) } \mathrm { NaOH } & \text { F) phenol } \
\hline \text { G) triethylamine } & \text { H) } \mathrm { HClO } & \text { I) } \mathrm { NH } _ { 3 } \
\hline
\end{array}$$ 
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 2

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 4.1 * 10^-⁵.

Accepted Answer

The answer of Calculate the equilibrium constant for the reaction...

Question 3

Calculate the ratio of the molarities of HPO₄²^- 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

The answer of Calculate the ratio of the molarities of...

Question 4

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

The answer of A buffer solution contains 0.25 M NaNO₂(aq)...

Question 5

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer B(aq)/BHCl(aq).The K_b of B is 1.5 * 10^-⁵.

Accepted Answer

The answer of Calculate the equilibrium constant for the reaction...

Question 6

The following compounds are available as 0.10 M aqueous solutions. $$\begin{array} { | l | l | l | } 
\hline \text { A) pyridine } & \text { B) } \mathrm { LiClO } _ { 4 } & \text { C) } \mathrm { HClO } _ { 4 } \
\hline \text { D) } \mathrm { HClO } _ { 2 } & \text { E) } \mathrm { NaOH } & \text { F) phenol } \
\hline \text { G) triethylamine } & \text { H) } \mathrm { HClO } & \text { I) } \mathrm { NH } _ { 3 } \
\hline
\end{array}$$ 
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 7

Calculate the equilibrium constant for the reaction that occurs when nitric acid is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 1.2 * 10 ^-⁵.

Accepted Answer

The answer of Calculate the equilibrium constant for the reaction...

Question 8

At the stoichiometric point in the titration of 0.260 M CH₃NH₂(aq) with 0.260 M HCl(aq),

Accepted Answer

At the stoichiometric point in the titration of a weak base (like CH₃NH₂) with a strong acid (HCl), the solution is acidic, hence the pH is less than 7. This is because the weak base is converted to its conjugate acid, which partially dissociates to release H⁺ ions, lowering the pH.

Question 9

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

Using the Henderson-Hasselbalch equation for the second dissociation, pH = pKa2 + log([CO3^2-]/[HCO3^-]), we find the ratio [CO3^2-]/[HCO3^-] = 10^(pH - pKa2) = 10^(9.0 - 10.0) = 0.1.

Question 10

At the stoichiometric point in the titration of 0.130 M HCOOH(aq) with 0.130 M KOH(aq),

Accepted Answer

At the stoichiometric point in the titration of a weak acid (HCOOH) with a strong base (KOH), the solution is basic because the conjugate base of the weak acid (HCOO-) is present in solution. This results in a pH greater than 7.

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

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 the sodium salt of the conjugate base (NaA) to form HA, which is a weak acid, thus maintaining the buffer's pH.

Question 13

The following compounds are available as 0.10 M aqueous solutions. $$\begin{array} { | l | l | l | } 
\hline \text { A) pyridine } & \text { B) } \mathrm { LiClO } _ { 4 } & \text { C) } \mathrm { HClO } _ { 4 } \
\hline \text { D) } \mathrm { HClO } _ { 2 } & \text { E) } \mathrm { NaOH } & \text { F) phenol } \
\hline \text { G) triethylamine } & \text { H) } \mathrm { HClO } & \text { I) } \mathrm { NH } _ { 3 } \
\hline
\end{array}$$ 
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 14

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 addition of NaOH will consume the acetic acid and produce more acetate ions, shifting the equilibrium to the right. The new concentration of acetic acid can be calculated using the Henderson-Hasselbalch equation:```pH = pKa + log([A-]/[HA])```where [A-] is the concentration of acetate ions and [HA] is the concentration of acetic acid.The initial concentration of acetic acid is 0.0200 M, and the initial concentration of acetate ions is also 0.0200 M. After the addition of 2.0 mmol of NaOH, the concentration of acetic acid will decrease by 2.0 mmol/L, and the concentration of acetate ions will increase by 2.0 mmol/L. Therefore, the new concentrations of acetic acid and acetate ions will be:```[HA] = 0.0200 M - 2.0 mmol/L = 0.0180 M[A-] = 0.0200 M + 2.0 mmol/L = 0.0220 M```Substituting these values into the Henderson-Hasselbalch equation, we get:```pH = 4.75 + log(0.0220/0.0180) = 4.84```Therefore, the correct answer is D) 4.84.

Question 15

The following compounds are available as 0.10 M aqueous solutions. $$\begin{array} { | l | l | l | } 
\hline \text { A) } \mathrm { HCl } & \text { B) aniline } & \text { C) } \mathrm { HCN } \
\hline \text { D) } \mathrm { KOH } & \text { E) methylamine } & \text { F) } \mathrm { HClO } \
\hline \text { G) } \mathrm { HClO } _ { 2 } & \text { H) } \mathrm { NaClO } _ { 2 } & \text { I) triethylamine } \
\hline
\end{array}$$ 
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 16

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 is a weak base. This reaction helps maintain the pH of the buffer solution by using up the added strong base without significantly changing the pH.

Question 17

The following compounds are available as 0.10 M aqueous solutions. $$\begin{array} { | l | l | l | } 
\hline \text { A) } \mathrm { HCl } & \text { B) aniline } & \text { C) } \mathrm { HCN } \
\hline \text { D) } \mathrm { KOH } & \text { E) methylamine } & \text { F) } \mathrm { HClO } \
\hline \text { G) } \mathrm { HClO } _ { 2 } & \text { H) } \mathrm { NaClO } _ { 2 } & \text { I) triethylamine } \
\hline
\end{array}$$ 
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...

Question 18

Calculate the equilibrium constant for the reaction that occurs when perchloric acid is added to the buffer B(aq)/BHCl(aq).The K_b of B is 3.4 * 10^-⁵.

Accepted Answer

The answer of Calculate the equilibrium constant for the reaction...

Question 19

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 20

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.

Quiz 6: Reactions

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 4.1 * 10^-⁵.

Calculate the ratio of the molarities of HPO₄²^- 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 0.25 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?

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer B(aq)/BHCl(aq).The K_b of B is 1.5 * 10^-⁵.

Calculate the equilibrium constant for the reaction that occurs when nitric acid is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 1.2 * 10 ^-⁵.

At the stoichiometric point in the titration of 0.260 M CH₃NH₂(aq) with 0.260 M HCl(aq) ,

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.

At the stoichiometric point in the titration of 0.130 M HCOOH(aq) with 0.130 M KOH(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.

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 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.

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 equilibrium constant for the reaction that occurs when perchloric acid is added to the buffer B(aq)/BHCl(aq).The K_b of B is 3.4 * 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.

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.

Quiz 6: Reactions

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer HA(aq)/NaA(aq).The Ka of HA is 4.1 * 10-5.

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 0.25 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?

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer B(aq)/BHCl(aq).The Kb of B is 1.5 * 10-5.

Calculate the equilibrium constant for the reaction that occurs when nitric acid is added to the buffer HA(aq)/NaA(aq).The Ka of HA is 1.2 * 10 -5.

At the stoichiometric point in the titration of 0.260 M CH3NH2(aq) with 0.260 M HCl(aq) ,

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.

At the stoichiometric point in the titration of 0.130 M HCOOH(aq) with 0.130 M KOH(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.

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 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.

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 equilibrium constant for the reaction that occurs when perchloric acid is added to the buffer B(aq)/BHCl(aq).The Kb of B is 3.4 * 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.

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.

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 4.1 * 10^-⁵.

Calculate the ratio of the molarities of HPO₄²^- 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 0.25 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?

Calculate the equilibrium constant for the reaction that occurs when sodium hydroxide is added to the buffer B(aq)/BHCl(aq).The K_b of B is 1.5 * 10^-⁵.

Calculate the equilibrium constant for the reaction that occurs when nitric acid is added to the buffer HA(aq)/NaA(aq).The K_a of HA is 1.2 * 10 ^-⁵.

At the stoichiometric point in the titration of 0.260 M CH₃NH₂(aq) with 0.260 M HCl(aq) ,

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.

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 0.0200 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.

Calculate the equilibrium constant for the reaction that occurs when perchloric acid is added to the buffer B(aq)/BHCl(aq).The K_b of B is 3.4 * 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.

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.