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Experiment 4 Guide Questions for Discussion

Iron-Silver Equilibrium

1. Give the balanced net ionic equation for the reaction between Fe2+ and Ag+. What is the chemical formula of the gray precipitate? Answer:
Fe2+(aq) + Ag+ (aq) Fe3+(aq) + Ag (s)
The formula of the precipitate is Ag(s).
2. Give the balanced net ionic equation for the reaction of Fe2+ with Fe(CN)63-. a. What is the chemical formula of the Prussian blue precipitate? b. How does the formation of the Prussian blue precipitate affect the reaction in (1)? Answer:

Fe2+ + Fe(CN)63- Fe[Fe(CN)6]-
a. The formula of the Prussian blue precipitate is [Fe(CN)6]-.
b. The formation of the Prussian blue precipitate decreases the [Fe2+], forcing the reaction in (1) to shift towards reactants. 3. Give the balanced net ionic equation for the reaction of Fe3+ and SCN-. c. What is the chemical formula of the blood red complex? d. How does the formation of the blood red complex affect the reaction in (1)? Answer:

Fe3+ + SCN- FeSCN2+
a. The formula of the blood red complex is FeSCN2+.
b. The formation of the blood red complex decreases [Fe3+], forcing the reaction in (1) to shift towards products. 4. Give the balanced net ionic equation for the reaction between Ag+ and Cl-. e. What is the chemical formula of the white precipitate? f. How does the formation of the white precipitate affect the reaction in (1)? Answer:

Ag+(aq) + Cl-(aq) AgCl(s)
a. The chemical formula of the white precipitate is AgCl. b. The formation of the white precipitate decreases [Ag+], forcing the reaction in (1) to shift towards reactants. 5. The fact that Fe2+, Fe3+, and Ag+ are present in the supernate tells us that the range of the Keq for the reaction in (1) is (choose one, and explain): a) Keq> 100

b) Keq< 0.01
c) 0.01<Keq<100

Answer: (c.) 0.01<Keq<100
The components Fe2+, Fe3+, and Ag+ are present in the supernate. This concludes that the mixture is at equilibrium and Keq cannot exceed to 100 nor it would be less than 0.01.

Copper-Ammonia Equilibrium

6. At the beginning of the reaction between Cu2+ and NH3(when only a few drops of ammonia have been added): g. What is the color of the precipitate formed?
h. What is the identity of the precipitate formed?
i. Explain how this precipitate formed. Provide the net ionic equation. 7. When the precipitate has dissolved upon addition of more ammonia, what is the color of the solution? What copper complex is responsible for this? 8. Provide the balanced net ionic equation for the formation of this copper complex. 9. Explain how the addition of HCl decolorized the solution. 10. Give the balanced net ionic equation for the reaction responsible for the shift in equilibrium for this system.

Answer:
j. (a) a white precipitate is formed (b) caused by the formation of Cu(OH)2 (c) which is described by the equation Cu2+ + 2OH- Cu(OH)2 since ammonia is present as an aqueous solution, thus the reacts w/ the hydroxide part to yield Cu(OH)2 k. (a) when the concentration of ammonia is considerably high, the solution transforms into a blue solution (b) caused by the formation of Cu(NH3)42+. l. When HCl is added into the solution, [Cl-] increases, adding up to the probability of decreasing [NH3] and then reverted back the solution to its previous color. m. The equation is given by NH4+ + Cl- NH4Cl in which ammonium chloride is present in the solution though it is colorless and cannot be seen directly in the solution but is implied by reverting back to pale blue color of the copper ion.

Chromate-Dichromate Equilibrium

11. What is the color of the chromate solution? Of the dichromate solution? 12. Which species (CrO42- or Cr2O72-) changed color when acid was added? when base was...
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