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CHM 2730 – SP24 Name________________________ Homework Assignment #6 (out of 64 pts) Due: 8:00am, Wednesday, February 28, 2024 I certify that the work below is my own, I have not copied the work from someone else, nor have I searched for these answers on the internet. I have completed all of the work on this assignment. Signature________________________________________________________ For full credit, show all work (each step) in detail, including cancellation of units. You also need to express your answer to the proper number of significant figures and show units. Copper (II) hydroxide is considered essentially insoluble in water due to its very low 𝐾𝐾𝑠𝑠𝑠𝑠 value. 𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)2 (𝑠𝑠) ⇋ 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) + 2 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) 𝐾𝐾𝑠𝑠𝑠𝑠 = 4.8 × 10−20 Recall that compounds considered “insoluble” in water will dissolve to some (albeit sometimes an undetectable) extent. However, if higher concentrations of the counterion (in this case 𝑂𝑂𝐻𝐻 − ) cause formation of soluble complex ions with 𝐶𝐶𝑢𝑢2+ , more 𝐶𝐶𝑢𝑢2+ may dissolve than would be calculated in pure water for the above equilibrium. Consider the following equilibria and cumulative formation constants (from Harris 9th ed. Appendix F) for the reaction of 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) and 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎): 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) + 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) ⇋ 𝐶𝐶𝐶𝐶𝐶𝐶𝐻𝐻 + (𝑎𝑎𝑎𝑎) 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) + 2 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) ⇋ 𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)2 (𝑎𝑎𝑎𝑎) 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) + 3 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) ⇋ 𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)− 3 (𝑎𝑎𝑎𝑎) 𝐶𝐶𝑢𝑢2+ (𝑎𝑎𝑎𝑎) + 4 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑞𝑞) ⇋ 𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)2− 4 (𝑎𝑎𝑎𝑎) 𝐾𝐾𝑠𝑠𝑠𝑠 = 3.16 × 106 𝛽𝛽2 = 6.31 × 1011 𝛽𝛽3 = 3.16 × 1014 𝛽𝛽4 = 3.98 × 1015 Thus, the total 𝐶𝐶𝐶𝐶 present in the presence of 𝑂𝑂𝐻𝐻 − can be written as: 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝐶𝐶𝐶𝐶 2− = [𝐶𝐶𝑢𝑢2+ ] + [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)+ ] + [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)2 ] + [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)− 3 ] + [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)4 ] 1 1) (20 pts) Using the example covered in lecture as a model (𝑃𝑃𝑏𝑏 2+ complexes with iodide 𝐼𝐼 − ), which is also discussed in the text, [𝐶𝐶𝑢𝑢2+ ], [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)+ ], 2− [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)2 ](𝑎𝑎𝑎𝑎), [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)− 3 ], [𝐶𝐶𝐶𝐶(𝑂𝑂𝑂𝑂)4 ], and Total dissolved 𝐶𝐶𝐶𝐶 for a fixed concentration of 𝑂𝑂𝐻𝐻 − = 0.0010 M. Show your work. 2 2) (20 pts) Repeat the calculations from part a) but this time for a fixed concentration of 𝑂𝑂𝐻𝐻 − = 1.00 M. Show your work. 3 3) (11 pts) Complete the following table using the results from parts a) and b), again, using the example in lecture as a guide. [𝑶𝑶𝑯𝑯− ] 0.0010 [𝑪𝑪𝒖𝒖𝟐𝟐+ ] [𝑪𝑪𝑪𝑪(𝑶𝑶𝑶𝑶)+ ] 𝟐𝟐− [𝑪𝑪𝑪𝑪(𝑶𝑶𝑶𝑶)𝟐𝟐 ] [𝑪𝑪𝑪𝑪(𝑶𝑶𝑶𝑶)− 𝟑𝟑 ] �𝑪𝑪𝑪𝑪(𝑶𝑶𝑶𝑶)𝟒𝟒 � Total dissolved Cu 1.00 4) (3 pts) What is(are) the major form(s) of dissolved Cu when in the presence of 0.0010 M 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) ? 5) (3 pts) What is(are) the major form(s) of dissolved Cu when in the presence of 1.00 M 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎) ? 6) (4 pts) Is there a significant difference in the major forms of dissolved Cu for 0.0010 M vs 1.00 M 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎)? If there is, explain why there would be a difference. 7) (3 pts) Compare the Total dissolved Cu in the presence of the two different concentrations of 𝑂𝑂𝐻𝐻 − (𝑎𝑎𝑎𝑎). Does what you observe make sense? Why or why not? 4

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