Lab 9

Question 1

what was the observation of the following reaction?
Cu(s) + 4HNO3 (aq)→Cu(NO3)2(aq) + 2NO2(aq) + 2H2O(l)

Answer 1

copper dissolved, brown gas appeared, solution was slime green then water was added and solution turned light transparent blue

Question 2

what was observed in the following reaction?

Balanced chemical equation: Cu(NO3)2 (aq) + 2NaOH(aq) → Cu(OH)2 (s) + 2NaNO3 (aq)

Net ionic equation: Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)

Answer 2

turned royal blue in color, turned cloudy and viscous, and precipitate formed Cu(OH)2

Question 3

what occured in the following reaction?

Balanced chemical equation: Cu(OH)2 (s) Δ→ CuO(s) + H2O(l)

Net ionic equation: Cu(OH)2 (s) Δ→ CuO(s) + H2O(l)

Answer 3

turned grey blue, then turned black
precipitate was dark brown

Question 4

what occured when adding HCl to the black solution?

Answer 4

yellow green color

Question 5

In solution what color is, [Cu(NH3)4(H2O)2]
2+

Answer 5

white gas formed and solution turned midnight dark blue

Question 6

what occurred when adding sulfuric acid to the [Cu(NH3)4(H2O)2]2+ ?

Answer 6

transparent light blue color

Question 7

what was observed in the following reaction?

CuSO4 (aq) + Zn(s) → Cu(s) + ZnSO4 (aq)

Answer 7

colorless solution with a burgundy precipitate and hydrogen gas was formed

Question 8

what is the appearance of recovered copper?

Answer 8

burgundy color shaped like kidney stones

Question 9

what is a redox reaction?

Answer 9

a reaction involving the change in oxidation state (transfer of electrons)

Question 10

Why is the large excess of Zn needed? How did you remove the unreacted zinc? Why?

Answer 10

The large excess of Zn is needed to ensure all the copper in solution is being reacted. The excess zinc was removed by adding HCl which dissolved the zinc but not the copper. The reaction of HCl and zinc caused bubbling which is an indicator that a reaction is occuring. In doing this it ensured that the copper would be as pure as possible.