Acid-Base Review-Answers
1. What is the Arrhenius definition of an acid and a base?
Acid: ionizes to produce a H+ion
Base: ionizes to produce OH-
2. Define acid and base according to Bronsted-Lowry
Acid: a proton donor
Base: a proton acceptor
3. In the following reaction identify Bronsted-Lowry acids, bases and conjugate acid base pairs:
a. HCO3-(aq) + HS-(aq) <-> CO32- + H2S(aq)
Acid Base CB CA
b. HSO4-(aq) + NO2-(aq) <-> HNO2(aq) + SO42-(aq)
Acid Base CA CB
c. HSO3-(aq) + HBO32-(aq) <-> H2BO3-(aq) + SO32-(aq)
Acid Base CA CB
4. Predict the equilibrium position for the reactions in question 3. (products or reactants favored?)
a) Reactants favored (<50%)
b) Products favored (>50%)
c) Products favored (>50%)
5. A solution has a pH of 6.5 and contains a few drops of phenolphthalein, methyl red and thymol blue. The solution will appear to be what color?
Phenolphthalein: colorless
Methyl red: yellow
Thymol blue: yellow
*yellow
6. What is the pH of a solution in which phenol red turns orange?
6.6-8.0
7. What color would you expect congo red to turn in a pH of 2.8?
Blue
8. An unknown solution turns bromocresol green to blue, Bromothymol blue, yellow and Chlorophenol red orange. What is the pH range of the solution? Which indicator was not useful in determining the range?
Bromocresol green-blue-5.4-14
Bromothymol blue-yellow- 0-6.0
Chlorphenol red-orange-5.2-6.8
Range: 5.4-6.0
9. Use the 5 step method to predict the acid-base reaction and the equilibrium position between hydrofluoric acid and sodium sulfate.
HF and Na2SO4
HF, Na+, SO42-, H2O
SA SB A/B
HF(aq) + SO42-(aq) ßà F-(aq) + HSO4-(aq)
Reactants favored.
10. Use the 5 step method to predict the acid-base reaction and the equilibrium position between carbonic acid and sodium hydroxide. Give the diagnostic.
H2CO3 NaOH
H2CO3, Na+, OH-, H2O
SA SB A/B
H2CO3(aq) +OH-(aq) ßà H2O(l) + HCO3-(aq) Products favored.
11. Calculate:
a) pH if the hydrogen ion concentration is 3.7 x 10-3 2.43
b) pOH if the hydrogen ion concentration is 2.3 x 10-6 8.36
c) pH if the hydroxide ion concentration is 4.1 x 10-9 5.61
d) [H+] if pOH is 12.23 1.7x10-2M
e) [OH-] if pH is 2.31 2.0x10-12M
f) [OH-] if pOH is 13.12 7.6 x 10-14M
12. Calculate the [H+] if the [OH-] is 3.2 x 10-7. 3.1x10-8M
13. In 0.1M solution of methanoic acid, [H+] =4.2 x 10-3M. Calculate the Ka of methanoic acid.
Ka= 1.8x10-4
14. In exactly 0.2M solution of a monoprotic weak acid, [H+] =9.86 x 10-4M. What is the Ka for this acid?
ka=4.9x10-6
15. A solution of a weak acid, exactly 0.500M, has a [H+] =5.77 x 10-6M. Calculate Ka. What is the pH of this solution?
pH=5.239
ka= 6.66x10-11
16. What is the pH of a 0.10 M solution of hydrofluoric acid?
pH=2.09
17. What is the hydrogen ion concentration of a 2.3 mmol/L solution of nitric acid?
HNO3 -> H+ + NO3-
2.3mmol 2.3mmol 2.3mmol
18. The hydrogen ion concentration in a 0.100 M solution of propanoic acid is determined to be 1.16 x 10-3 mol/L. Calculate the percent ionization of propanoic acid.
P=1.16 %
19. When a 0.125 M aqueous solution of benzoic acid reaches equilibrium, the pH of the solution is 2.55. Calculate the Ka value and the percent ionization.
Ka=6.3 x 10-5
P=2.3 %
20. Use this pH curve to answer these questions:
a. Is the sample being titrated an acid or a base? Explain. Sample is an acid because the curve starts near pH=2
b. What is the titrant? Strong base
c. Estimate the end point. 6.
d. Choose a suitable indicator for this reaction.
Chlorophenol red
21. A 20.0ml sample of 0.300mol/L NaOH is required to react completely with 30.0 ml of nitrous acid. What is the concentration of the nitrous acid?
0.200mol/L
22. A sample of arsenic acid H3AsO4 was titrated with sodium hydroxide. The titration had 2 end points. Write the reaction for the titration.
H3AsO4 +2NaOH à Na2HAsO4 + 2HOH
23. In a chemical analysis, 25.0 ml of sulfuric acid was titrated to the second end point with 0.358 mol/L KOH. In the titration, an average volume of 18.2 ml was required. Calculate the molar concentration of the sulfuric acid.
I0.130.mol/L
24. Several 10.0 mL vinegar samples were titrated with a standardized 0.582 mol/L solution of sodium hydroxide. An average volume of 13.8 mL of sodium hydroxide was required to reach the phenolphthalein endpoint. What is the concentration of the vinegar solution?
0.803mol/L
25. A sodium borate solution was titrated to the second endpoint with 0.241 mol/L hydrobromic acid. An average volume of 15.2 mL of hydrobromic acid was required to react with 20.0 mL samples of sodium borate, Calculate the concentration of sodium borate. Sketch the pH curve for this reaction.
0.0916mol/L