Question
The pH versus volume data for the titration of 0.10M \(HNO_2(aq)\) with 0.10M \(KOH(aq)\) is plotted on the graph above. Based on the data, which of the following species is present in the greatest concentration after 6.0mL of \(KOH(aq)\) has been added to the solution of \(HNO_2(aq)\) ?
A \(H^+(aq)\)
B \(HNO_2(aq)\)
C \(NO_2^−(aq)\)
D \(OH^−(aq)\)
▶️Answer/Explanation
Ans:C
At the half-equivalence point in a titration of a weak acid with a strong base, \([HA]=[A^−]\). Based on the data, the half-equivalence point is reached after 5mL of \(KOH(aq)\) has been added. After this point, \([NO_2^−]>[HNO_2]\). Because \(HNO_2\) is a weak acid and the majority of the acid has reacted at this point, \([H^+]\) is very low. Before the equivalence point, \(OH^− \) added to the solution is consumed by the reaction with \(HNO_2(aq)\). Therefore, the species in the greatest concentration after 6.0mL of \(KOH(aq)\) has been added to the solution of \(HNO_2(aq)\) is \(NO_2^−(aq)\).
Question
A 60.mL sample of \(NaOH(aq)\) was titrated with 0.10M \(HCl (aq)\). Based on the resulting titration curve shown above, what was the approximate concentration of \(NaOH(aq)\) in the sample?
A 0.033M
B 0.050M
C 0.10M
D 0.20M
▶️Answer/Explanation
Ans:B
Using the titration curve, the volume of \(HCl \) required to reach the equivalence point is 30.mL (or 0.030L); hence, the number of moles of \(HCl \) is \((0.030L)(0.10mol/L)=0.0030mol\). The mole ratio for the reaction between \(HCl \) and \(NaOH(aq)\) is 1:1; therefore, the number of moles of \(HCl \) consumed is equal to the number of moles of \(NaOH(aq)\) in the sample. The concentration of \(NaOH(aq)\) in the 60.mL sample is \((0.0030mol / 0.060 L)=0.050M\).
Question
\(5 H_2O_2(aq) + 2 MnO_{4} ̄(aq) + 6 H^{+}(aq)\) → (\2 Mn^{2+}(aq) + 8 H_{2}O(l) + 5 O_{2}(g)\)
In a titration experiment,\( H_{2}O_{2}(aq)\) reacts with aqueous\( MnO_4^{+}(aq) \)as represented by the equation above. The dark purple \(KMnO_{4}\) solution is added from a buret to a colorless, acidified solution of\( H_{2}O_{2}\)(aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.)
Which of the following best describes what happens to the pH of the \(H_2O_2\) solution as the titration proceeds?
(A) The +2 charge on the manganese ions maintains the acidity of the solution.
(B) The production of water dilutes the solution, making it basic.
(C) As \(H^{+}\) ions are consumed, the solution becomes less acidic and the pH increases.
(D) As \(H^{+}\) ions are consumed, the solution becomes less acidic and the pH decreases.
▶️Answer/Explanation
Ans:C
Question
A student performs an acid-base titration and plots the experimental results in the graph above. Which of the following statements best explains the experimental findings?
(A) A strong acid was titrated with a strong base, as evidenced by the equivalence point at pH = 7.
(B) A strong acid was titrated with a strong base, as evidenced by the equivalence point at pH > 7.
(C) A weak acid was titrated with a strong base, as evidenced by the equivalence point at pH > 7.
(D) A weak acid was titrated with a weak base, as evidenced by the equivalence point at pH approximately 7.
▶️Answer/Explanation
Ans:C