Question
Which of the following gives the best estimate for the pH of a \(5\times 10^{−4}\)M \(Sr(OH)_2(aq)\) solution at 25°C?
A pH≈3.0 because \(Sr(OH)_2(aq)\) is a strong acid.
B pH≈5.0 because \(Sr(OH)_2(aq)\) is a weak acid.
C pH≈9.0 because \(Sr(OH)_2(aq)\) is a weak base.
D pH≈11.0 because \(Sr(OH)_2(aq)\) is a strong base.
▶️Answer/Explanation
Ans:D
\(Sr(OH)_2(aq)\) is a strong base, and its complete dissociation produces 2 moles of \(OH^−\) ions per mole of \(Sr(OH)_2(aq)\) that dissolves. As a result, \([OH^−]=2\times (5\times 10^{−4}M)=1\times 10^{−3}M\) and pOH≈3.0, so pH≈11.0.
Question
Which of the following gives the best estimate for the pH of a \(1\times 10^{−5}\) M\(HClO_4\)(aq) solution at 25°C?
A pH≈1.0 because \(HClO_4\) is a strong acid.
B pH≈5.0 because \(HClO_4\) is a strong acid.
C pH≈7.0 because \(ClO_4^-\) is a strong base.
D pH≈9.0 because \(ClO_4^-\) is a strong base.
▶️Answer/Explanation
Ans:B
Since \(HClO_4\) is a strong acid, it dissociates completely, producing 1 mol of \(H_3O^+\) per 1 mol of \(HClO_4\)(aq). Therefore, \(pH=−log[H_3O^+]=−log[HClO_4]initial=−log(1\times 10^{−5})\)≈5.0 . (In general, the negative log of \(10^{−x}\) is x. Therefore, the negative log of \(1\times 10^{−5}\) is 5.)
Question
Which of the following is the correct mathematical relationship to use to calculate the pH of a 0.10M aqueous HBr solution?
A \(pH = [H_3O^+]=0.10\)
B \(pH =−log(1.0\times 10^{−1})\)
C \(pH=7.00−(0.10)\)
D \(pH=log(1.0\times 10^{−1})\)
▶️Answer/Explanation
Ans:B
By definition, pH=\(−log[H_3O^+]\). In this case, pH\(=−log(1.0\times 10^{−1})\), since for a strong acid like HBr, it is assumed that the acid ionizes 100% and \([HBr]_{initial}=[H_3O^+]\).
Question
When 200. of 2.0 M NaOH(aq) is added to 500. mL of 1.0 M HCl(aq), the pH of the resulting mixture is closest to
(A) 1.0
(B)3.0
(C) 7.0
(D) 13.0
▶️Answer/Explanation
Ans:A
Question
When 200. of 2.0 M NaOH(aq) is added to 500. mL of 1.0 M HCl(aq), the pH of the resulting mixture is closest to
(A) 1.0
(B)3.0
(C) 7.0
(D) 13.0
▶️Answer/Explanation
Ans:A
Question
The pH of a 0.01 M \(HNO_{2}\)(aq) solution is in which of the following ranges? (For\( HNO_{2}\)(aq), Ka =\( 4.0 × 10^{-4} )\)
(A) Between 1 and 2
(B) Between 2 and 3
(C) Between 4 and 5
(D) Between 6 and 7
▶️Answer/Explanation
Ans:C
Question
Which of the following correctly ranks the three monoprotic acids listed in the table above from the weakest to the strongest?
(A) X < Y < Z
(B) X < Z < Y
(C) Y < Z < X
(D) Z < Y < X
▶️Answer/Explanation
Ans:D