Some examples from this set of practice questions
1.
Which of following will raise the pH of a weak acid HA in aqueous solution? (Check all possible answers) A. Addition of water B. Addition of NaCl C. Making a buffered solution by adding NaA(s) D. Addition of HNO3 E. Titrating with KOH
Answer: E. Titrating with KOH Explanation: The addition of a strong base like KOH will raise the pH and cause it to be more basic
2.
Which indicator would be best for the titration of a weak acid (Ka=6.4 x 10^-5) with a strong base, whose pH at the equivalence point is 8.17? A. thymolphthalein (9.5-10.5) B. methyl orange (3.2-4.4) C. crystal violet (0.2-1.8) D. thymol blue (7.7-9.3)
Answer: D. thymol blue (7.7-9.3) Explanation: the pH of 8.17 will fall in that range and thus the color of the solution will turn thymol blue at the equivalence point (when number of moles of acid and base are equal)
3.
What is the pH at the half equivalence point of the titration in the previous question? A. 5.87 B.8.13 C.10.93 D.4.19
Answer: D. 4.19 Explanation: Equivalence point is when number of moles of acid and base are equal At the half-equivalence point, pH = pKa when titrating a weak acid pKa=-log Ka =- log (6.4x10^-5) =4.19
4.
A 75.0-ml sample of 0.065 M HCN (Ka=6.2x10^-10) is titrated with 0.65M NaOH. What volume of 0.65M NaOH is required to reach the stoichiometric point? A. 750 mL B. 7.50mL C. 3.75 mL D. 75.0 mL
Answer: B. 7.5mL The stoichiometric point is the equivalence point. This is a weak acid and a strong base titration. M1V1=M1V1 (0.0650M x 75ml) = 0.65M x Vol 7.5mL of NaOH
5.
Which of the following is the net ionic equation for the reaction that occurs during the titration of nitric acid with potassium hydroxide? A. H+ + OH- -> H2O B. HNO3 + H2O -> NO3- + H3O+ C. HNO3 + KOH -> K+ +NO3- + H2O D. HNO3 + OH- -> NO3- + H2O
Answer: A. H+ + OH- -> H2O Explanation: Nitric acid (HNO3) is a strong acid and potassium hydroxide (KOH) is a strong base. Thus, they will both dissociate completely or in other words separate into ions. HNO3 + KOH -> K+ + NO3- + H2O Cross out same ions on both sides so the NO3- and K+ leaving the following H+ + OH- -> H2O
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