Q: Given $$K_a$$ for $$\mathrm{HA} is$$ $$1.8 \times 10$$^{-5}$$, what is the value of K_b$ for its conjugate base $$\mathrm{A^-}$$ at 25°C?

$$K_b = 5.6 \times 10$$^{-10}$$

Question 1

Which of the following correctly identifies the Brønsted-Lowry acid and its conjugate base in the reaction: $$\mathrm{$$HClO_4$$} + \mathrm{H_2O} \rightarrow \mathrm{H_3O^+} + \mathrm{$$ClO_4$$^-}$$?

Accepted Answer

Acid: $$\mathrm{$$HClO_4$$}$$; Conjugate base: $$\mathrm{$$ClO_4$$^-}$$

Question 2

A 0.115 M solution of $$\mathrm{$$HNO_2$$}$$ has a $$K_a = 4.5 	imes 10$$^{-4}$$. What is the pH of the solution? (Assume x$$ \ll 0.115$$)

Accepted Answer

$$\mathrm{pH} = 2.04$$

Question 3

Given $$K_a$$ for $$\mathrm{HA} is$$ $$1.8 	imes 10$$^{-5}$$, what is the value of K_b$ for its conjugate base $$\mathrm{A^-}$$ at 25°C?

Accepted Answer

$$K_b = 5.6 	imes 10$$^{-10}$$

Question 4

Which of the following acids is the strongest, and which of their conjugate bases is the weakest?

Accepted Answer

Strongest acid: $$\mathrm{$$HClO_4$$}$$; Weakest conjugate base: $$\mathrm{$$ClO_4$$^-}$$

Question 5

The pH of a 0.14 M solution of a monoprotic acid is 1.95. What is the $$K_a of $$the acid?

Accepted Answer

$$K_a = 1.3 	imes 10$$^{-2}$$

Question 6

Which of the following best describes the solution when $$\mathrm{Na_2CO_3} is $$dissolved in water?

Accepted Answer

Basic, because $$\mathrm{CO_3$^{2-}}$$ hydrolyzes to form $$\mathrm{OH^-}$$

Question 7

Arrange the following 0.1 M solutions in order of increasing pH: $$\mathrm{$$HNO_3$$}$$, $$\mathrm{NaClO}$$, $$\mathrm{KCl}$$, $$\mathrm{NH_4Cl}$$, $$\mathrm{NaOH}.$$

Accepted Answer

$$\mathrm{$$HNO_3$$} \u003c \mathrm{NH_4Cl} \u003c \mathrm{KCl} \u003c \mathrm{NaClO} \u003c \mathrm{NaOH}$$

Question 8

A buffer is prepared by mixing 0.20 mol of $$\mathrm{NH_3$}$$ and 0.20 mol of $$\mathrm{NH_4Cl} in 1.0 L of $$solution. What is the pH of the buffer? ($$K_b$$ for $$\mathrm{NH_3$} = 1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$\mathrm{pH} = 9.25$$

Question 9

Which of the following best explains why $$\mathrm{H_2O}$$ can act as both an acid and a base?

Accepted Answer

Because it can both donate and accept a proton ($$\mathrm{H^+})$$

Question 10

Which titration curve best represents the titration of a weak acid with a strong base?

Accepted Answer

A curve with an initial low pH, a buffer region, and an equivalence point above pH 7

Question 11

A buffer solution is made by mixing equal concentrations of $$\mathrm{CH_3COOH}$$ and $$\mathrm{CH_3COO^-}$$ ($$K_a = 1.8 	imes 10$$^{-5}$$). What is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = 4.74$$

Question 12

Which of the following would result in a buffer solution?

Accepted Answer

Mixing $$\mathrm{HCOOH}$$ and $$\mathrm{HCOONa}$$

Question 13

Given the redox reaction: $$\mathrm{$$MnO_4$$^-} + 5\mathrm{Fe$$^{2+}$$} + 8\mathrm{H^+} \rightarrow \mathrm{Mn$$^{2+}$$} + 5\mathrm{Fe$$^{3+}$$} + 4\mathrm{H_2O}$$, which species is the oxidizing agent?

Accepted Answer

$$\mathrm{$$MnO_4$$^-}$$

Question 14

In the galvanic cell diagram $$\mathrm{Zn(s) | Zn$$^{2+}$$(aq) || Cu$$^{2+}$$(aq) | Cu(s)}$$, which half-cell is the anode?

Accepted Answer

$$\mathrm{Zn(s) | Zn$$^{2+}$$(aq)}$$

Question 15

Which of the following best describes the function of a salt bridge in a galvanic cell?

Accepted Answer

It maintains electrical neutrality by allowing ion flow between half-cells

Question 16

Balance the following redox reaction in acidic solution: $$\mathrm{Cr_2O_7$$^{2-}$$} + \mathrm{Fe$$^{2+}$$} \rightarrow \mathrm{Cr$$^{3+}$$} + \mathrm{Fe$$^{3+}$$}$$

Accepted Answer

$$\mathrm{Cr_2O_7$$^{2-}$$} + 6\mathrm{Fe$$^{2+}$$} + 14\mathrm{H^+} \rightarrow 2\mathrm{Cr$$^{3+}$$} + 6\mathrm{Fe$$^{3+}$$} + 7\mathrm{H_2O}$$

Question 17

Which of the following statements about the equivalence point in the titration of a weak acid with a strong base is correct?

Accepted Answer

The pH at the equivalence point is greater than 7

Question 18

A student adds 0.200 g of NaOH to 1.00 L of a buffer solution containing 0.10 M $$\mathrm{CH_3COOH}$$ and 0.10 M $$\mathrm{CH_3COO^-}. $$What will happen to the pH of the buffer?

Accepted Answer

The pH will increase slightly

Question 19

Which of the following best explains why $$\mathrm{Cu$$^{2+}$$} is $$reduced in the reaction $$\mathrm{Zn(s) + Cu$$^{2+}$$(aq) \rightarrow Zn$$^{2+}$$(aq) + Cu(s)}$$?

Accepted Answer

Because it gains electrons from zinc

Acids, Bases, Buffers, and Electrochemistry: General Chemistry II Study Notes

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