Chapter III: Introduction to Eh pH Diagrams
Quiz Solutions
1. Indicate which combination of the following words/phrases statements is correct.
The standard reduction potential is a measure of the tendency to accept electrons and be reduced relative to the standard H+/H2 electrode.
2. Which of the following statements are true? Use T or F to indicate True or False.
(i) An oxidizing agent accepts electrons and gets oxidized F
(ii) A reducing agent accepts electrons and gets oxidized F
(iii) A reducing agent accepts electrons and gets reduced F
(iv) A reducing agent loses electrons and gets oxidized T
(v) An oxidizing agent accepts electrons and gets reduced T
(vi) An oxidizing agent loses electrons and gets oxidized F
(vii) A reducing agent loses electrons and gets reduced F
(viii) An oxidizing agent loses electrons and gets reduced F
3. Consider the following two couples.
MnO₄⁻ / Mn⁺² E° = 1.51 V
CO₂ /H₂C₂O₄ E° = -0.43 V
Calculate the standard cell potential in volts.
1.51 V – (-0.43 V) = 1.94 V
4. There are a number of nickel sulfides that are important in hydrometallurgy and pyrometallurgy. Relevant thermodynamic data are provided in the table below.
(a) There are four Ni(II) species (not including NiS). List them:
Ni+2/NiOH+/Ni(OH)2/Ni(OH)3-
(b) Using hydrolysis states, what should be the order in which they appear from left to right on the Eh-pH diagram?
*Ni+2*, *NiOH+*, *Ni(OH)2*, *Ni(OH)3-*
(c) We will ignore Ni(OH)3- . For the remaining three calculate the buffer pH values (vertical lines) that separate them on the diagram.
Ni+2/NiOH+ pH: *9.916*
NiOH+/Ni(OH)2 pH: *3.884*
(d) One of the Ni(II) species will not appear on the diagram under the given conditions. Indicate which one. What vertical line is required instead? Calculate its pH.
*NiOH+*
pH: *6.9/6.90/6.900*
5. Ni-S-H 2 O diagram: The sulfur-water diagram is available in the course notes.
Which is the hydrolysis reactions for dissociation of NiS into Ni(II) and S(-II) species.
NiS + 2H+ = Ni+2 + H2S
