CHEM20018
Week 6 Tutorial Problems
1. In regard to the Ellingham diagram below, answer the following questions.
a) What chemical reactions are represented by the lines in the diagram?
b) What does the gradient of each line represent?
c) Why do some lines show discontinuities?
d) Is carbon capable of reducing silica? If so, under what conditions?
e) At what temperature will carbon reduce NiO? What will be the product of the oxidation of carbon?
f) Is Li capable of reducing Al2O3? If so, under what conditions?
2. The Latimer diagram for V in acidic conditions is presented below:
a) Write the half equation for the reduction of VO2+(aq) to V3+(aq) and calculate the E° value.
b) Write the half equation for the reduction of V3+(aq) to V(s) and calculate the E° value.
c) Indicate which species, if any, will undergo disproportionation to the adjacent species in the diagram.
d) Give the comproportionation reaction for the formation of V3+(aq) from VO2+(aq) and V2+(aq) and calculate the E° value for the reaction.
e) For the comproportionation reaction in part (d), calculate the value of DG° .
f) Write the equation for the disproportionation of V3+ to VO2+(aq) and V2+(aq) and calculate the value ofK for this reaction.
3. The Frost diagram for manganese in acidic conditions is presented below.
a) According to the graph what is the strongest oxidising agent?
b) For the species identified in part (a) give the reduction half reaction and the accompanying E° value.
c) According to the graph, considering only the oxidised forms of manganese, what is the weakest oxidising agent? Give the equation for the reduction half-reaction and the accompanying E° value.
d) Give the half equation and E° value for the reduction of HMnO4-(aq) to Mn2+(aq) .
e) MnO2(s) is a relatively stable solid. How does the Frost diagram indicate this? Suggest a reason for its relatively high stability.
4. The Pourbaix diagram for plutonium provides important information regarding its chemical form. when it enters the natural environment. Plutonium is capable of existing in the following forms: Pu, Pu3+, Pu4+, PuO2, PuO22+, PuO3 and Pu2O3.
a) In the graph below label the various regions of the diagram with the appropriate chemical species.
b) Give the reactions for the conversion of species separated by vertical lines.
c) Give the reactions for the conversion of species separated by horizontal lines.
d) Give the reaction for the conversion between species separated by the steepest diagonal line.
e) Give the mathematical equation for the line represented in part (d).
f) What factor determines the gradient of the diagonal lines?
g) What is the dominant form. of plutonium in a marine environment?
Supplementary Questions
S1. The group 1 metals are able to undergo oxidation with O2 to form a variety of solid products.
a) Indicate the products formed from the combination of the group 1 metals with excess O2.
b) How does a superoxide differ from a peroxide.
c) What is a sub-oxide?
d) Why is Li2O referred to as an anti-fluorite structure?
S2. Using the following two equations estimate the concentration of I- ions in a 1.0 x 10-3 M solution of AgNO3 to which solid AgI has been added (T= 298 K).
You may assume after the system has reached equilibrium that solid AgI remains immersed in the solution.