Q: A 0.25 M solution of ammonia ($NH_3$) has a $K_b$ of $1.8 \times 10^{-5}$. What is the $[OH^-]$ in the solution? (Assume $x$ is small compared to 0.25)

$[OH^-] = \sqrt{K_b \times [NH_3]} = \sqrt{1.8 \times 10^{-5} \times 0.25} = 2.12 \times 10^{-3}$ M

Question 1

Which of the following statements best describes a strong electrolyte?

Accepted Answer

It completely dissociates in water, producing only ions in solution and conducts electricity well.

Question 2

Which of the following compounds is a strong acid?

Accepted Answer

HNO\_3

Question 3

A solution of NaCl in water conducts electricity because:

Accepted Answer

NaCl dissociates completely into Na\^+ and Cl\^- ions, which move freely in solution.

Question 4

Which of the following is NOT a strong base?

Accepted Answer

NH\_3

Question 5

According to the Arrhenius definition, which of the following is classified as a base?

Accepted Answer

A substance that produces OH\^- ions in aqueous solution.

Question 6

Which of the following acids is diprotic?

Accepted Answer

H\_2SO\_4

Question 7

A 0.15 M solution of HCl is prepared. What is the pH of the solution?

Accepted Answer

$\mathrm{pH} = -\log(0.15) = 0.82$

Question 8

Which statement correctly describes the dissociation of a weak acid in water?

Accepted Answer

It partially dissociates, resulting in an equilibrium between ions and non-ionized molecules.

Question 9

Which of the following is the correct expression for the acid dissociation constant $K_a$ for acetic acid ($CH_3COOH$)?

Accepted Answer

$K_a = \dfrac{[CH_3COO^-][H_3O^+]}{[CH_3COOH]}$

Question 10

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

Accepted Answer

They dissociate in a stepwise manner, with each step having a different $K_a$ value.

Question 11

A 0.25 M solution of ammonia ($NH_3$) has a $K_b$ of $1.8 	imes 10^{-5}$. What is the $[OH^-]$ in the solution? (Assume $x$ is small compared to 0.25)

Accepted Answer

$[OH^-] = \sqrt{K_b 	imes [NH_3]} = \sqrt{1.8 	imes 10^{-5} 	imes 0.25} = 2.12 	imes 10^{-3}$ M

Question 12

Which of the following is a Brønsted-Lowry base?

Accepted Answer

A substance that accepts a proton.

Question 13

Which of the following is the correct relationship between pH and pOH in aqueous solution at 25°C?

Accepted Answer

$\mathrm{pH} + \mathrm{pOH} = 14$

Question 14

Which of the following is a Lewis acid?

Accepted Answer

A substance that accepts an electron pair.

Question 15

A solution has $[H_3O^+] = 1.0 	imes 10^{-4}$ M. What is its pH?

Accepted Answer

$\mathrm{pH} = -\log(1.0 	imes 10^{-4}) = 4.00$

Question 16

Which of the following is true about non-electrolytes?

Accepted Answer

They do not dissociate in water and do not conduct electricity.

Question 17

Which of the following is a triprotic acid?

Accepted Answer

H\_3PO\_4

Question 18

A 0.10 M solution of acetic acid ($K_a = 1.8 	imes 10^{-5}$) is prepared. What is the approximate $[H_3O^+]$ in the solution? (Assume $x$ is small compared to 0.10)

Accepted Answer

$[H_3O^+] = \sqrt{K_a 	imes [CH_3COOH]} = \sqrt{1.8 	imes 10^{-5} 	imes 0.10} = 1.34 	imes 10^{-3}$ M

Question 19

Which of the following best explains why $Ba(OH)_2$ is a strong base?

Accepted Answer

It is a Group IIA metal hydroxide and dissociates completely in water to produce $Ba^{2+}$ and $2OH^-$ ions.

Electrolytes, Acids, and Bases: Key Concepts and Definitions

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