Progress check 8.2 (11 -->18)

The weak acid  $CH_3COOH$   has a pKa of 4.76. A solution is prepared by mixing 500.mL of 0.150M  $CH_3COOH$  and 0.0200mol of NaOH(s). Which of the following can be used to calculate the pH of the solution?

• pH=4.76 + log $\left(\frac{0.0200}{0.150}\right)=3.88$  

• pH = 4.76 + log $\left(\frac{0.0200}{0.0750}\right)=4.19$  

• pH = 4.76 + log $\left(\frac{0.0200}{0.0550}\right)=4.32$  

• pH = 4.76 + log $\left(\frac{0.0950}{0.0750}\right)=4.86$  

Which of the following provides the correct mathematical expression to calculate the pH of a solution made by mixing 10.0ml of 1.00MHCl and 11.0mL of 1.00MNaOH at 25^oC?

• pH=−log(0.0010)=3.00pH=−log(0.0010)=3.00

• pH=14.00+log(0.001)=11.00

• pH = 14.00 + log $\left(\frac{0.0010}{0.0210}\right)=12.68$

• pH = 14.00 + log $\left(\frac{0.0010}{0.0110}\right)=12.96$

A buffer solution is formed by mixing equal volumes of 0.12 M NH₃(aq) and 0.10 M HCl(aq), which reduces the concentration of both solutions by one half. Based on the pKa data given in the table, which of the following gives the pH of the buffer solution?

• pH=−log(0.050)=1.30

• pH = 9.25 + log $\left(\frac{0.010}{0.050}\right)=8.55$

• pH = 9.25 + log $\left(\frac{0.060}{0.050}\right)=9.32$

• pH = 14.00 -(-log(0.010)) = 12.00

The pH versus volume data for the titration of 0.10 M HNO₂(aq) with 0.10 M KOH(aq) is plotted on the graph above. Based on the data, which of the following species is present in the greatest concentration after 6.0mL of KOH(aq) has been added to the solution of HNO₂(aq) ?

• H⁺(aq)

• HNO₂(aq)

• NO₂^-(aq)

• OH⁻(aq)

A 0.20M solution of the weak acid potassium hydrogen phthalate (KHP) is titrated with 0.10MNaOH(aq). Based on the titration curve shown in the graph above, the pK_a of KHP is closest to which of the following?

Answer D

• 3.6

• 5.4

• 8.8

• 11.8

A 60.mL sample of NaOH(aq) was titrated with 0.10MHCl(aq). Based on the resulting titration curve shown above, what was the approximate concentration of NaOH in the sample?

• 0.033M

• 0.050M

• 0.10M

• 0.20M

The table above provides information on two weak acids. Which of the following explains the difference in their acid strength?

• Acid 1 is a stronger acid because it has more acidic hydrogen atoms than acid 2.

• Acid 1 is a stronger acid because it can make more hydrogen bonds than acid 2.

• Acid 2 is a stronger acid because it is a larger, more polarizable molecule with stronger intermolecular forces than acid 1.

• Acid 2 is a stronger acid because it has a more stable conjugate base than acid 1 due to the greater number of electronegative Br atoms.

The equilibrium reactions for diprotic oxoacids with a general formula H₂XO₄ are represented by the equations above. The acid ionization constants for H₂SeO₄ and H₂TeO₄ are provided in the table. Which of the following best explains the difference in strength for these two acids?

• H₂SeO₄ is weaker because SeSe has a smaller positive formal charge than Te, resulting in a decrease in its ability to transfer an H⁺ to H₂O.

• H₂TeO₄ is weaker because Te has a smaller positive formal charge than Te, resulting in a decrease in its ability to transfer an H⁺ to H₂O.

• H₂SeO₄ is weaker because SeSe is more electronegative than Te, resulting in more stable conjugate bases HSeO₄⁻ and SeO₄²⁻ than those for H₂TeO₄ .

• H₂TeO₄ is weaker because TeTe is less electronegative than Se, resulting in less stable conjugate bases HTeO₄⁻ and TeO₄²⁻ than those for H₂SeO₄.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2

Lewis diagrams of the weak bases NH₃ and NF₃ are shown above. Based on these diagrams, which of the following predictions of their relative base strength is correct, and why?

• NF₃ is a stronger base than NH₃ because more than one resonance structure exists for its conjugate acid NF₃H⁺, making it more stable than NH₄⁺.

• NF₃ is a stronger base than NH₃ because of the greater electronegativity of F compared with H.

• NF₃ is a weaker base than NH₃ because of the greater electronegativity of F compared with H.

• NF₃ is a weaker base than NH₃ because more than one resonance structure exists for its conjugate acid NF₃H⁺, making it more stable than NH₄⁺.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2