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Oxidizing Cu with concentrated nitric acid, HNO3 in aqueous form
Typology: Lab Reports
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In this experiment, you will carry out a series of reactions to transform copper into various forms and learn more about the three main types of chemical reactions: precipitation, acid-base neutralization, and redox reactions. You will also determine the efficiency of the overall transformation cycle by calculating the percentage of starting material recovered at the end of the experiment.
The chemistry behind each step is described in the Background section of this experiment. The procedures required to carry out each step are described below.
You should include one table that contains the mass of copper at the beginning and end of the experiment along with % of copper recovered. This table should include:
Record observations for all of the steps (I-V) of the copper cycle in your lab book. Be sure to label each step (I-V). The observations for each step should include:
Your observations should include state(s) of matter, color, texture, smell, etc. where applicable. If your observations are not detailed, you may not receive full credit.
One step also requires a specific chemical test using litmus paper to check for acidity. Be sure to also record the results of these tests in your lab notebook.
**You will turn in worksheet pages 6-7 along with the copies of your observations from your lab notebook.
on skin must be rinsed immediately with water for 15 minutes. Any acid spilled on your work area must be neutralized then the entire area should be washed and dried. CAUTION: Concentrated nitric acid reacts with copper metal to form brown toxic NO 2 gas. Leave the reaction beaker in the fume hood until all of the brown gas is vented in the hood.
Step II: Chemistry - Precipitating Cu(OH) 2 (s) with NaOH (aq) In Part II, two reactions are carried out by adding NaOH (aq). In the first reaction, the hydroxide ions (OH–^ ) from the NaOH (aq) neutralize the excess hydronium ions (H 3 O+) left over from the previous part.
Once all the H 3 O+^ ions are neutralized, additional OH–^ ions react with the Cu 2+ complex ion to form a gelatinous blue Cu(OH) 2 precipitate.
Once all the Cu2+^ ions have reacted, no more precipitate forms. Adding more OH–^ ions makes the solution basic, so it can turn red litmus paper blue. The picture sequence on the next page outlines the step-by-step process that occurs during this step.
Figure 2: Step-wise Illustration of the Precipitation of Cu(OH) 2 in Part II OH -
OH-
OH-
[Cu(H 2 O) 6 ]+
[Cu(H 2 O) 6 ]+
Cu(OH) (^2)
OH- OH- OH-
H 3 O +
H 3 O +
H 3 O + [Cu(H 2 O) 6 ] +
[Cu(H 2 O) 6 ] +
OH -
Part II Step 1
H 3 O+
H 3 O+
H 3 O+ [Cu(H 2 O) 6 ] +
[Cu(H 2 O) 6 ] +
At end of Part I
OH-
OH-
OH- OH- neutralizes H 3 O +
Part II Step 2 OH- reacts with [Cu(H 2 O) 6 ] +2^ to form Cu(OH) 2 (s)
OH-
OH-
[Cu(H 2 O) 6 ] +
Cu(OH) (^2) Part II Step 3 Excess OH- makes the solution basic
1 st^ Beaker : At the end of Part I, hydrated copper complex, Cu 2+^ are present, making the solution blue, and excess hydronium ions (H 3 O+) remain from the nitric acid used.
2 nd^ Beaker : Adding NaOH (aq) to the blue solution results in the OH –^ ions neutralizing the H 3 O+^ ions to form water: H 3 O+ (aq) + OH– (aq) → 2 H 2 O (l). The Na +^ ions and resulting water molecules are not shown.
3 rd^ and 4 th^ Beakers : Once all the H 3 O+^ are neutralized, adding more NaOH (aq) results in the OH–^ ions reacting with the Cu 2+^ to form the blue Cu(OH) 2 (s) precipitate shown at the bottom of the beaker. Water molecules released from the complex ion are not shown.
5 th^ Beaker : When all of the Cu 2+^ ions have been converted to Cu(OH) 2 (s) precipitate, adding more NaOH (aq) results in unreacted OH–^ ions in solution, which makes the solution basic. Red
Step 1: Fold filter paper in half and crease lightly.
Step 2: Fold again into quarters.
Step 3: Lift up one layer of the filter paper, leaving 3 layers below. Place the filter paper cone into the funnel. Press the edges of the filter paper against the sides of the funnel, and wet the single-sided edge with deionized water, so the paper sticks to the funnel.
Finally, place the plastic funnel in the small ring clamp, and place a 400-mL beaker beneath it to collect the filtrate (the liquid that goes through the filter paper). The funnel’s stem should be just inside the beaker to prevent splashing.
Step IV: Procedure - Dissolving CuO(s) with sulfuric acid, H 2 SO 4 (aq)
CAUTION: Sulfuric acid, H 2 SO 4 (aq) , is corrosive, so it can cause severe chemical burns and damage clothing. Handle with care and avoid breathing the fumes. Any sulfuric acid spilled on skin must be rinsed immediately with water for 15 minutes. Any acid spilled on your work area must be neutralized, and the entire area should be washed and dried.
Step V: Procedure - Reducing Cu 2+^ ions with Zn Metal
Wash and dry all of your glassware, equipment, and your lab area to prevent chemical contamination and potential hazards.
Calculating Percent Copper Recovered Theoretically, the mass of Cu recovered should be equal to the mass of the original Cu sample. The overall efficiency of the experiment is measured by calculating the percentage of copper recovered:
massofinitialsample
massoffinalproduct percent recovered= × [11]
Ideally, the percent recovered should be close to 100%, which indicates that most (if not all) of the copper was successfully transformed through all five parts of the experiment.
A student performing this experiment started with a 0.3769 g sample of copper turnings, which was dissolved in concentrated nitric acid. After completing the series of reactions, the student isolated 0. g of copper. Calculate the percent copper recovered by the student.
a. The solution was not basic before being heated in Part III. High Low
b. In Part III, the solution was poured into the funnel until it went above the top of the filter paper, and some black solid was disposed of with the filtrate. High Low
c. The solution decanted in Part V was slightly blue in color. High Low
d. After all the copper metal was obtained in Part V, it took too long for the excess Zn granules to dissolve, so a student added concentrated nitric acid to the solution, resulting in a brown gas. High Low
e. In Part V, the copper metal was weighed after it turned dark brown/red. High Low