Q: A solution is prepared by mixing acetic acid ($$CH_3COOH) $$and sodium acetate ($$CH_3COONa). $$Which equation should be used to calculate the pH of this buffer solution?

Henderson–Hasselbalch equation: $$\text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right)$$

Question 1

Which of the following statements best describes the relationship between the acid dissociation constant ($$K_a) $$and the base dissociation constant ($$K_b) $$for a conjugate acid–base pair?

Accepted Answer

The product of $$K_a$$ and $$K_b$$ equals the ion-product constant for water: $$K_a 	imes K_b = K_w$$

Question 2

A solution is prepared by mixing acetic acid ($$CH_3COOH) $$and sodium acetate ($$CH_3COONa). $$Which equation should be used to calculate the pH of this buffer solution?

Accepted Answer

Henderson–Hasselbalch equation: $$	ext{pH} = 	ext{p}K_a + \log \left( \frac{[	ext{A}^-]}{[	ext{HA}]} ight)$$

Question 3

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

Accepted Answer

Sodium acetate ($$CH_3COONa)$$

Question 4

A student titrates 25.0 mL of 0.100 M hydrochloric acid ($$HCl) $$with 0.100 M sodium hydroxide ($$NaOH). $$What is the pH at the equivalence point?

Accepted Answer

pH = 7.00

Question 5

Which of the following best explains why the solubility of $$CaF_2$$ decreases in the presence of $$NaF$$?

Accepted Answer

The common-ion effect: addition of $$F^-$$ shifts the equilibrium toward precipitation.

Question 6

Which of the following is an amphoteric substance?

Accepted Answer

Aluminum hydroxide ($$Al(OH)_3)$$

Question 7

A buffer is made by mixing 0.50 mol of $$NH_4Cl$$ and 0.50 mol of $$NH_3 in 1.0 L of $$solution. If the $$K_b$$ for $$NH_3 is$$ $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer? (K_w = 1.0$$ 	imes $$10^{-14})$$

Accepted Answer

pH = 9.25

Question 8

Which of the following best describes the process of balancing a redox equation in acidic solution?

Accepted Answer

Balance atoms other than H and O, add $$H_2O to $$balance O, add $$H^+ to $$balance H, add electrons to balance charge.

Question 9

Which battery type is commonly used in smartphones due to its high energy density and rechargeability?

Accepted Answer

Lithium ion battery

Question 10

A voltaic cell is constructed using a zinc electrode in $$ZnSO_4$$ and a copper electrode in $$CuSO_4. $$Which equation correctly relates the standard cell potential ($$E^\circ_{cell}) to $$the standard reduction potentials?

Accepted Answer

$$E^\circ_{cell} = E^\circ_{red,\,cathode} - E^\circ_{red,\,anode}$$

Question 11

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

Accepted Answer

The equilibrium constant for autoionization is $$K_w = [H^+][OH^-]$$

Question 12

A solution contains $$Ag^+$$ and $$Pb^{2+}$$ ions. Which reagent can be used to selectively precipitate $$Ag^+$$ without precipitating $$Pb^{2+}$$?

Accepted Answer

Add $$Cl^-$$ ions to form $$AgCl ($$low $$K_{sp}$$), leaving $$Pb^{2+} in $$solution.

Question 13

Which of the following is the correct expression for the solubility product constant ($$K_{sp}) $$for $$BaSO_4$$?

Accepted Answer

$$K_{sp} = [Ba$$^{2+}$$][SO_4$^{2-}]$$

Question 14

During the corrosion of iron, which species acts as the oxidizing agent?

Accepted Answer

Oxygen ($$O_2)$$

Question 15

Which of the following best describes the effect of increasing temperature on the solubility of most solid salts in water?

Accepted Answer

Solubility increases as temperature increases for most salts.

Question 16

A solution is prepared by dissolving $$NH_4NO_3 in $$water. Which statement best describes the acid–base properties of the resulting solution?

Accepted Answer

The solution is acidic because $$NH_4$$^+$$ acts as a weak acid.

Question 17

Which of the following equations correctly relates the standard cell potential ($$E^\circ_{cell}) to $$the Gibbs free energy change ($$\Delta G^\circ$$)?

Accepted Answer

$$\Delta G^\circ = -nFE^\circ_{cell}$$

Question 18

A buffer solution is prepared using 0.10 M $$CH_3COOH$$ and 0.10 M $$CH_3COONa. If 0.01 $$mol of $$HCl is $$added to 1.0 L of this buffer, what will happen to the pH?

Accepted Answer

The pH will decrease slightly, but the buffer will resist large changes.

Question 19

Which of the following best describes the qualitative analysis of metallic elements?

Accepted Answer

Grouping ions based on their solubility and reactivity to identify them.

Acid-Base Equilibria, Solubility, and Electrochemistry: Exam 3 Study Guide

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