Chemical Reactions of Copper 6 and Percent Yield – 1. Initial mass of copper -2. Mass of copper and evaporating dish – 3. Mass of evaporating dish 4. Mass of recovered copper , 5. Percent yield (show calculations) % yield-reca era mass cre- $83 6. Describe the reaction Cu(s)+HNO, (a copper dissaveds addad once sired itchemes to 7. Describe the reaction Cu(NO3)2(ag)+ NaOH(ag) 8. Describe the reaction Cu(OH)2(6)- 9. What are you removing by this washing? CuO 10. What copper compound is present in the beaker? C, sO 11. Describe the reaction CuSO4(ag)+ Zn(s) or CuSO4(ag)+A(). 12. What is present in solution? 13. What is the gas? 14. How do you know? 15. What are you removing by washing? 16. What color is your copper sample? reddisn boun – 17. Is it uniform in appearance? Yes 1 18. Soggest possible sources of error in this experiment. 75 2015 rson Education, nc.
The Correct Answer and Explanation is :
In this experiment, copper undergoes a series of chemical reactions, and you are tasked with calculating the percent yield and analyzing the reactions. Here’s a breakdown of the key steps:
1. Initial mass of copper
This is the starting mass of the copper metal before any reactions take place.
2. Mass of copper and evaporating dish
This is the combined mass of the evaporating dish and the copper after the first step, typically after copper reacts with nitric acid.
3. Mass of evaporating dish
This is the mass of the dish alone after the copper has been removed, leaving behind any residue.
4. Mass of recovered copper
This is the mass of copper recovered after completing the experiment, which is used to calculate the percent yield.
5. Percent yield
The percent yield is calculated by comparing the actual mass of copper recovered to the theoretical mass that could be recovered if the reaction proceeded perfectly. The formula for percent yield is:
[
\text{Percent Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100
]
For example, if the actual yield is 83 grams and the theoretical yield is 100 grams:
[
\text{Percent Yield} = \left( \frac{83}{100} \right) \times 100 = 83\%
]
6. Describe the reaction Cu(s) + HNO₃ →
Copper reacts with nitric acid (HNO₃) to form copper nitrate (Cu(NO₃)₂) and produce nitrogen dioxide (NO₂) gas.
[
\text{Cu} (s) + 2\text{HNO}_3 (aq) \rightarrow \text{Cu(NO}_3)_2 (aq) + H_2O (l) + NO_2 (g)
]
This is a redox reaction where copper is oxidized to Cu²⁺.
7. Describe the reaction Cu(NO₃)₂(aq) + NaOH(aq) →
Copper nitrate reacts with sodium hydroxide (NaOH) to form copper hydroxide (Cu(OH)₂), a blue precipitate.
[
\text{Cu(NO}_3)_2 (aq) + 2\text{NaOH} (aq) \rightarrow \text{Cu(OH)}_2 (s) + 2\text{NaNO}_3 (aq)
]
8. Describe the reaction Cu(OH)₂(s) →
Copper hydroxide decomposes to form copper oxide (CuO) and water when heated.
[
\text{Cu(OH)}_2 (s) \rightarrow \text{CuO} (s) + H_2O (l)
]
9. What are you removing by this washing?
By washing with water, you are removing any soluble impurities like NaNO₃ and excess NaOH.
10. What copper compound is present in the beaker?
After washing and heating, the remaining copper compound is copper oxide (CuO), a black solid.
11. Describe the reaction CuSO₄(aq) + Zn(s) or CuSO₄(aq) + Al(s) →
Copper sulfate reacts with zinc or aluminum to displace copper from its ionic form and form zinc sulfate or aluminum sulfate. This is a single displacement reaction.
[
\text{CuSO}_4 (aq) + \text{Zn} (s) \rightarrow \text{Cu} (s) + \text{ZnSO}_4 (aq)
]
12. What is present in solution?
The solution contains either zinc sulfate (ZnSO₄) or aluminum sulfate (Al₂(SO₄)₃), depending on which metal was used.
13. What is the gas?
The gas produced is hydrogen (H₂) from the displacement reaction.
14. How do you know?
You can confirm the presence of hydrogen gas by performing a “pop test” where the gas is ignited, producing a characteristic popping sound.
15. What are you removing by washing?
By washing, you are removing any excess acid (H₂SO₄), sulfate salts, and unreacted metal.
16. What color is your copper sample?
The recovered copper will be reddish-brown, characteristic of pure copper.
17. Is it uniform in appearance?
Yes, it should be uniform, but some copper may have an uneven surface due to impurities or the reaction process.
18. Suggest possible sources of error in this experiment:
Possible sources of error include:
- Incomplete reaction (not all copper reacts)
- Loss of copper during transfer or washing
- Impurities in the chemicals or glassware
- Inaccurate measurements (e.g., mass measurements)
- Contamination of copper during recovery or drying
This experiment involves several reactions that transform copper through various chemical states. The key to success is careful handling and accurate measurements to ensure reliable percent yield calculation.