Q: A buffer solution is prepared by mixing $$0.10\ \mathrm{mol} of $$acetic acid ($$\mathrm{CH_3COOH}) $$and $$0.10\ \mathrm{mol} of $$sodium acetate ($$\mathrm{CH_3COONa}) in$$ $$1.0\ \mathrm{L} of $$water. If the $$K_a of $$acetic acid is $$1.8 \times 10$$^{-5}$$, what is the pH of the buffer?

$$\mathrm{pH} = -\log_{10}(1.8 \times 10$$^{-5}$$) \approx 4.74$$

Q: A solution is prepared by dissolving $$0.20\ \mathrm{mol} of$$ $$\mathrm{H_2CO_3} in$$ $$1.0\ \mathrm{L} of $$water. If the first dissociation constant $$K_{a1} is$$ $$4.3 \times 10$$^{-7}$$, what is the concentration of $$\mathrm{H^+}$$ ions at equilibrium, assuming only the first dissociation occurs?

$$[\mathrm{H^+}] = \sqrt{K_{a1} \times [\mathrm{H_2CO_3}]} = \sqrt{4.3 \times 10$$^{-7}$$ \times 0.20} \approx 2.9 \times 10$$^{-4}$$\ \mathrm{M}$$

Question 1

Which of the following statements about strong acids is correct?

Accepted Answer

Strong acids completely dissociate in water, resulting in a high concentration of $$\mathrm{H^+}$$ ions.

Question 2

Which of the following is a polyprotic acid?

Accepted Answer

Sulfuric acid ($$\mathrm{H_2SO_4})$$

Question 3

A student titrates $$25.0\ \mathrm{mL} of$$ $$0.100\ \mathrm{M}$$ $$\mathrm{H_2SO_4}$$ with $$0.200\ \mathrm{M}$$ $$\mathrm{NaOH}. $$What volume of $$\mathrm{NaOH} is $$required to reach the equivalence point?

Accepted Answer

$$25.0\ \mathrm{mL}$$

Question 4

Which of the following equations correctly represents the dissociation of a strong monoprotic acid in water?

Accepted Answer

$$\mathrm{HA\ (aq) \rightarrow H^+\ (aq) + A^-\ (aq)}$$

Question 5

Which of the following is true about the pH of a $$0.01\ \mathrm{M}$$ solution of a strong acid?

Accepted Answer

The pH is calculated as $$-\log_{10}(0.01)$$, which equals 2.

Question 6

Which of the following statements best describes a weak acid?

Accepted Answer

A weak acid only partially dissociates in water, resulting in an equilibrium between the acid and its ions.

Question 7

A buffer solution is prepared by mixing $$0.10\ \mathrm{mol} of $$acetic acid ($$\mathrm{CH_3COOH}) $$and $$0.10\ \mathrm{mol} of $$sodium acetate ($$\mathrm{CH_3COONa}) in$$ $$1.0\ \mathrm{L} of $$water. If the $$K_a of $$acetic acid is $$1.8 	imes 10$$^{-5}$$, what is the pH of the buffer?

Accepted Answer

$$\mathrm{pH} = -\log_{10}(1.8 	imes 10$$^{-5}$$) \approx 4.74$$

Question 8

Which of the following is the correct expression for the acid dissociation constant $$K_a$$ for a generic weak acid $$\mathrm{HA}$$?

Accepted Answer

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

Question 9

A solution is prepared by dissolving $$0.20\ \mathrm{mol} of$$ $$\mathrm{H_2CO_3} in$$ $$1.0\ \mathrm{L} of $$water. If the first dissociation constant $$K_{a1} is$$ $$4.3 	imes 10$$^{-7}$$, what is the concentration of $$\mathrm{H^+}$$ ions at equilibrium, assuming only the first dissociation occurs?

Accepted Answer

$$[\mathrm{H^+}] = \sqrt{K_{a1} 	imes [\mathrm{H_2CO_3}]} = \sqrt{4.3 	imes 10$$^{-7}$$ 	imes 0.20} \approx 2.9 	imes 10$$^{-4}$$\ \mathrm{M}$$

Question 10

Which of the following best explains why titrations of polyprotic acids require knowledge of multiple $$K_a$$ values?

Accepted Answer

Each proton is lost in a separate step, each with its own equilibrium constant.

Question 11

A buffer solution is made by mixing $$0.20\ \mathrm{mol} of $$ammonia ($$\mathrm{NH_3$}) $$and $$0.10\ \mathrm{mol} of $$ammonium chloride ($$\mathrm{NH_4Cl}) in$$ $$1.0\ \mathrm{L} of $$water. If the $$K_b of $$ammonia is $$1.8 	imes 10$$^{-5}$$, what is the pOH of the buffer?

Accepted Answer

$$\mathrm{pOH} = \mathrm{p}K_b + \log_{10}\left(\dfrac{[\mathrm{NH_4$^+}]}{[\mathrm{NH_3$}]}\right) = 4.74 + \log_{10}(0.10/0.20) \approx 4.44$$

Question 12

Which of the following is a correct statement about the relationship between $$K_a$$ and $$K_b$$ for a conjugate acid-base pair?

Accepted Answer

$$K_a 	imes K_b = K_w$$

Question 13

A $$0.10\ \mathrm{M}$$ solution of a weak acid has a pH of 3.0. What is the $$K_a of $$the acid?

Accepted Answer

$$K_a = \dfrac{[\mathrm{H^+}]^2}{[\mathrm{HA}]} = \dfrac{(1.0 	imes 10$$^{-3}$$)^2$$}{0.10} = 1.0 	imes $$10^{-5}$

Question 14

Which of the following is the correct formula for calculating the pH of a buffer solution using the Henderson-Hasselbalch equation?

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a + \log_{10}\left(\dfrac{[\mathrm{A^-}]}{[\mathrm{HA}]}\right)$$

Question 15

During a titration of $$50.0\ \mathrm{mL} of$$ $$0.100\ \mathrm{M}$$ acetic acid with $$0.100\ \mathrm{M}$$ NaOH, what is the pH at the half-equivalence point? ($$K_a$$ for acetic acid is $$1.8 	imes 10$$^{-5}$$)

Accepted Answer

$$\mathrm{pH} = \mathrm{p}K_a = -\log_{10}(1.8 	imes 10$$^{-5}$$) \approx 4.74$$

Question 16

Which of the following best describes the role of a buffer in human blood?

Accepted Answer

It maintains the pH within a narrow range by neutralizing added acids and bases.

Question 17

Which of the following is the correct net ionic equation for the reaction between hydrochloric acid and sodium hydroxide?

Accepted Answer

$$\mathrm{H^+\ (aq) + OH^-\ (aq) \rightarrow H_2O\ (l)}$$

Question 18

A student accidentally adds twice the amount of strong base required to neutralize a weak acid during a titration. What will be the resulting solution?

Accepted Answer

The solution will be basic, with excess $$\mathrm{OH^-}$$ ions present.

Question 19

Which of the following is a correct statement about the titration curve of a weak acid with a strong base?

Accepted Answer

The pH at the equivalence point is greater than 7 due to the formation of a weak conjugate base.

General Chemistry Test #2: Syllabus and Exam Instructions

Guida di studio - Domande di pratica

Study guide - Flashcard