Help-General Chemistry

Help-General Chemistry II (CHE-112)

Section no.:

Semester and year:



Written Assignment 6: Reactions of Acids and Bases


Answer all assigned questions and problems, and show all work.


  1. Determine the pH of (a) a 0.40 M CH3CO2H solution, (b) a solution that is 0.40 M CH3CO2H and 0.20 M NaCH3CO2. (8 points)


(Reference: Chang 16.5)






  1. Which of the following solutions can act as a buffer? (a) KCl/HCl, (b) KHSO4/H2SO4, (c) KNO2/HNO2. (5 points)


(Reference: Chang 16.9)





  1. Calculate the pH of the buffer system made up of 0.15 M NH3/0.35 M NH4 (5 points)


(Reference: Chang 16.11)





  1. The pH of a bicarbonate-carbonic acid buffer is 8.00. Calculate the ratio of the concentration of carbonic acid (H2CO3) to that of the bicarbonate ion (HCO3). (5 points)


(Reference: Chang 16.13)






  1. The pH of a sodium acetate–acetic acid buffer is 4.50. Calculate the ratio [CH3COO]/[CH3COOH]. (5 points)


(Reference: Chang 16.15)






  1. Calculate the pH of the 0.20 M NH3/0.20 M NH4Cl buffer. What is the pH of the buffer after the addition of 10.0 mL of 0.10 M HCl to 65.0 mL of the buffer? (8 points)

(Reference: Chang 16.17)







  1. A 0.2688 g sample of a monoprotic acid neutralized 16.4 mL of 0.08133 M KOH solution. Calculate the molar mass of the acid. (5 points)


(Reference: Chang 16.27)







  1. In a titration experiment, 12.5 mL of 0.500 M H2SO4 neutralize 50.0 mL of NaOH. What is the concentration of the NaOH solution? (5 points)


(Reference: Chang 16.29)







  1. A 0.1276 g sample of an unknown monoprotic acid was dissolved in 25.0 mL of water and titrated with 0.0633 M NaOH solution. The volume of base required to bring the solution to the equivalence point was 18.4 mL. (a) Calculate the molar mass of the acid. (b) After 10.0 mL of base had been added during the titration, the pH was determined to be 5.87. What is the Ka of the unknown acid? (10 points)


(Reference: Chang 16.31)





  1. Calculate the pH at the equivalence point for the following titration: 0.20 M HCl versus 0.20 M methylamine (CH3NH3; Kb = 4.4 × 10–4) (5 points)


(Reference: Chang 16.33)





  1. A 25.0 mL solution of 0.100 M CH3COOH is titrated with a 0.200 M KOH solution. Calculate the pH after the following additions of the KOH solution: (a) 0.0 mL, (b) 5.0 mL, (c) 10.0 mL, (d) 12.5 mL, (e) 15.0 mL. (25 points)


(Reference: Chang 16.35)





  1. Referring to the following table:


Indicator Color in Acid Color in Base pH Range*
Thymol blue Red Yellow 1.2–2.8
Bromophenol blue Yellow Bluish purple 3.0–4.6
Methyl orange Orange Yellow 3.1–4.4
Methyl red Red Yellow 4.2–6.3
Chlorophenol blue Yellow Red 4.8–6.4
Bromothymol blue Yellow Blue 6.0–7.6
Cresol red Yellow Red 7.2–8.8
Phenolphthalein Colorless Reddish pink 8.3–10.0

*The pH range is defined as the range over which the indicator changes from the acid color to the base color.


Specify which indicator or indicators you would use for the following titrations:  (9 points)

  1. HCOOH versus NaOH
  2. HCl versus KOH
  3. HNO3 versus CH3NH2


(Reference: Chang 16.43)






  1. The pKa of butyric acid (HBut) is 4.7. Calculate Kb for the butyrate ion (But). (5 points)


(Reference: Chang 16.97)







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