Q: Which of the following statements about the autoionization of water is correct?

At 25°C, $$ [\mathrm{H_3O^+}] = [\mathrm{OH^-}] = 1.0 \times 10$$^{-7}$$ M in $$pure water.

Question 1

Which of the following statements correctly describes the relationship between acid strength and its conjugate base?

Accepted Answer

The stronger the acid, the weaker its conjugate base.

Question 2

Which of the following species acts as a Lewis acid but NOT as a Bronsted-Lowry acid in the reaction $$ \mathrm{BF_3$} + :\mathrm{NH_3$} \rightarrow \mathrm{F_3B{-}NH_3$} $$?

Accepted Answer

$$ \mathrm{BF_3$} $$

Question 3

A 0.10 M solution of acetic acid ($$ \mathrm{CH_3COOH} ) $$has a $$ K_a = 1.8 	imes 10$$^{-5}$$ . $$What is the pH of this solution? (Assume $$ x \ll 0.10 $$ for simplification.)

Accepted Answer

$$ \mathrm{pH} = 2.87 $$

Question 4

Which of the following best explains why $$ \mathrm{HI}  is a $$stronger acid than $$ \mathrm{HF} $$?

Accepted Answer

The H–I bond is weaker and easier to break than the H–F bond.

Question 5

A buffer solution is prepared by mixing 0.20 mol of $$ \mathrm{CH_3COOH} $$ and 0.10 mol of $$ \mathrm{CH_3COO^-}  in $$enough water to make 1.0 L of solution. Given $$ pK_a = 4.74 $$, what is the pH of the buffer?

Accepted Answer

$$ \mathrm{pH} = 4.44 $$

Question 6

Which of the following salts will produce a basic solution when dissolved in water?

Accepted Answer

$$ \mathrm{NaCH_3COO} $$

Question 7

Which of the following statements about the autoionization of water is correct?

Accepted Answer

At 25°C, $$ [\mathrm{H_3O^+}] = [\mathrm{OH^-}] = 1.0 	imes 10$$^{-7}$$  M in $$pure water.

Question 8

Which of the following is an amphiprotic species?

Accepted Answer

$$ \mathrm{$$HCO_3$$^-} $$

Question 9

Given $$ K_a(\mathrm{HCN}) = 4.9 	imes 10$$^{-10}$$ $$, what is the $$ K_b $$ for $$ \mathrm{CN^-}  at 25$$°C?

Accepted Answer

$$ 2.0 	imes 10$$^{-5}$$ $$

Question 10

Which of the following best describes the effect of dilution on the percent dissociation of a weak acid?

Accepted Answer

Percent dissociation increases as the acid is diluted.

Question 11

Which of the following is the correct expression for the acid dissociation constant $$ K_a $$ for the reaction $$ \mathrm{HA} + \mathrm{H_2O} \rightleftharpoons \mathrm{H_3O^+} + \mathrm{A^-} $$?

Accepted Answer

$$ K_a = \dfrac{[\mathrm{H_3O^+}][\mathrm{A^-}]}{[\mathrm{HA}]} $$

Question 12

Which of the following best explains why $$ \mathrm{$$HClO_4$$}  is a $$stronger acid than $$ \mathrm{$$HClO_2$$} $$?

Accepted Answer

$$ \mathrm{$$HClO_4$$} $$ has more oxygen atoms, which withdraw electron density and stabilize the conjugate base.

Question 13

A solution is prepared by dissolving $$ \mathrm{NH_4Cl}  in $$water. Which of the following statements is true about the resulting solution?

Accepted Answer

The solution will be acidic because $$ \mathrm{NH_4$^+} $$ acts as a weak acid.

Question 14

Which of the following is a correct statement about polyprotic acids?

Accepted Answer

The first dissociation step provides essentially all the $$ [\mathrm{H_3O^+}]  in $$solution.

Question 15

Which of the following best describes the relationship between $$ K_a $$, $$ K_b $$, and $$ K_w $$ for a conjugate acid-base pair at 25°C?

Accepted Answer

$$ K_a 	imes K_b = K_w $$

Question 16

Which of the following is a correct application of the Henderson-Hasselbalch equation?

Accepted Answer

If $$ [\mathrm{A^-}] \u003e [\mathrm{HA}] $$, then $$ \mathrm{pH} \u003e \mathrm{p}K_a $$ and the solution is more basic relative to $$ \mathrm{p}K_a .$$

Question 17

Which of the following is a correct statement about the behavior of $$ \mathrm{Cl^-}  in $$water?

Accepted Answer

$$ \mathrm{Cl^-}  is $$essentially neutral and does not act as a base.

Question 18

Which of the following best describes the effect of electronegative substituents near the acidic hydrogen in a molecule?

Accepted Answer

They stabilize the conjugate base, making the acid stronger.

Question 19

Which of the following is a correct statement about the $$ pK_a $$ and $$ pK_b  of a $$conjugate acid-base pair at 25°C?

Accepted Answer

$$ pK_a + pK_b = 14 $$

Question 20

Which of the following is a correct Lewis acid-base reaction?

Accepted Answer

$$ \mathrm{Cu$$^{2+}$$} + 4 :\mathrm{NH_3$} \rightarrow [\mathrm{Cu(NH_3$)_4}]^{2+} $$

Chapter 17: Acids and Bases – Comprehensive Study Notes

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