1. The assigned voltages for the Mg/Mg 2+ and Fe/Fe 2+ will deviate from expecte
ID: 971099 • Letter: 1
Question
1. The assigned voltages for the Mg/Mg2+ and Fe/Fe2+ will deviate from expected values due to impurities in the Mg strip and the Fe2+ solution, so consider the other half cells only when answering this question:
What is the significance of the difference between the tabulated Eo and Eassigned for each of the half cells? Explain your answer.
2. Discuss your data concerning cell voltage and its concentration dependence.
a. According to the Nernst equation, how much should the cell potential change if the aqueous component of one of the half cells is changed by a factor of 10? Does this agree with your experimental data?
b. What occured when Na2S was added? Does this result make sense in terms of the Nernst equation?
3a. What effect does replacing the water ligands in [Cu(H2O)6]2+ with ammonia ligands to form [Cu(NH3)4]2+ have on the half cell potential of Cu2+/Cu?
3b. Which species is a poorer oxidizing agent, [Cu(H2O)6]2+ or [Cu(NH3)4]2+? Explain your answer
3c. In the copper complexes investigated, the water and ammonia molecules act as Lewis bases (electron pair donors); they provide both of the electrons that form the covalent bonds between the Cu2+ ion and each ligand. Which ligand (H2O or NH3) is the stronger Lewis base? Explain your answer in terms of your answers for questions 3a and 3b. (hint: the poorer an oxidizing agent a species is, the harder it it to reduce that species. Hint #2: the copper complexes are reduced by gaining an electron.)
Explanation / Answer
1. For answering the first question, you have not given appropriate information
2. Nernest equation for electrochemical cells Ecell = E0(cell) -0.059/n log [ox]/[red];
(a) If [OX] concentration incresesd by a factor of 10 than, the cell potential is decreased by an amount of 0.059/n. if the concentration of [RED] increases by a factor of 10 than the cell EMF increased by a factor of 0.059/n.
(b) If Na2S is react with one of the metal ions resulting in decrease in that concentration. If Na2S react with oxidant its cell EMF decreases therwise if it reacts with reductant than its cell EMF increases.
3. (a) the effect can be explained simply on the basis of the strength of the ligands. Ammonia moleculs are more strengthful ligands than water molecules (see spectrochemical series of ligands). Thats the reacson why the transformation moves in forward direction and to form Cu-amine complex. In overall process the no electronic transformation observed so this complex formation and their transformations could not obtain any change in half cell potential.
(b) the so obtained Cu-amine complex is relatively stable then it is a poorer oxidizing agent.
(c) this effect again can be explained simply on the basis of the strength of the ligands. Ammonia moleculs are more strengthful ligands than water molecules (see spectrochemical series of ligands). Thats the reacson why the transformation moves in forward direction and to form Cu-amine complex. So ammonia is stronger Lewis base.
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