Need help with this lab: (sorry so long)
Hypothesis:
The amount of product will be regulated by the limiting reactant.
Procedure:
First, I took two test tubes from the Glassware shelf. I added 6 mL of the copper sulfate solution to one, and 6 mL of the sodium sulfide solution to the second. Then, I prepared the “test solution” and combined 20 mL of 6M NH3 solution and 5 mL of 0.4M ZnSO4 in a 50 mL beaker. After, I poured 2 mL of the test solution into each of the test tubes and recorded the resulting color and if there is a precipitate or not. I used these two test tubes as the standards to compare for the other trials. Then, I took a new test tube, my “reaction test tube,” and added 5 mL of CuSO4 and 1 mL of Na2S to it and recorded any changes that happened. After, I took another clean test tube, and decant the liquid from the reaction test tube into the new test tube. Then, I weighed the reaction test tube with the precipitate in the bottom and recorded the value.
After, I tested the test tube with the decanted liquid for excess reactant by adding 2 mL of the test solution to the beaker. Then, I compared the results with the two reference test tubes and recorded which reactants were present in the decanted liquid and were in excess in the reaction test tube. I repeated these steps for each of the four different solutions and recorded all the data.
Data:
CuS04 Standard 6CuSO4 0N2S(ml
dark blue
Na2S Standard 0CuSO4(ml) 6N2S(ml)
white
Test Tube a= 5CuSO4(ml) 1N2S(ml)
Mass+ppt* 18.210g darkblue
b= 4CuSO4(ml) 2N2S(ml)
mass+ppt* 18.219g dark blue
c= 3CuSO4(ml) 3Na2S(ml)
mass+ppt* 18.229g light blue
d= 2CuSO4(ml) 4B2S(ml)
Mass+ppt* 18.219g clear with white solid
e= 1CuSO4(ml) 5N2S(ml)
18.210g clear with white solid
*ppt = precipitate formed from the combination of Cu+2 and S-2.
**Observation/ Test result is appearance of the solution when 2 ml of the NH3 and ZnSO4 mixture is added.
Calculations/Interpretations: Show all math performed (give the formula, show your setup, and give the result. Use proper significant figures and include proper labels. Also, answer ALL questions asked in the lab.
1. Which test tubes have an excess of CuSO4 ?
2. Which test tubes have an excess of N2S?
3. Which test tube has the largest amount of precipitate?
Test tube c
Why? (Use terms such as limiting reactant and excess reactant to explain.)
4. What was the ratio of Cu+2 to S-2?
5. What is the chemical formula of copper (II) sulfide?
CuS
Conclusion: Your concluding statement should clearly summarize your results and show that you fully understand the concepts explored in your experiment. Begin by stating whether your hypothesis was true or false. Then support your statement using specific information from your data and calculations sections. Consider the following questions as you write your conclusion: What happened to result in the outcome you observed? What did you learn or what previously learned concept did this lab reinforce? How might you improve the experiment? Do you have any other comments you would like to share about this lab?
(*Note: Not all questions pertain to each lab.) Your conclusion should be approximately one paragraph in length
Is the first answer test tube a, b, and c? It seems too easy, so probably not right. I am going by the CuSO4 is the excess and thus the blue color.
I am doing this exact same lab. Was your answer- test tube a, b, and c have an excess of CuSO4 -correct? That is the same answer I got from doing the lab, and that is what I would recommend answering.
I'm sorry. I meant to also point out that the instructions say the Observation/Test Results are the observations AFTER you add the zinc and ammonia mixture. For "c" you must have put your observation before you added this mixture, because after this addition "c" should have been white. Therefore, "c" would not be an answer to put down to number 1. It would just be "a" and "b."
Which test tubes have an excess of N2S?
To answer the questions and complete the calculations, we need to analyze the given data and perform some calculations. Here's how you can do it:
1. To determine the test tubes with an excess of CuSO4, look at the observations of the test tubes. If there is no precipitation or if the color does not change significantly, it means there is an excess of CuSO4. From the observations given:
- Test Tube a: Dark blue precipitate
- Test Tube b: Dark blue precipitate
- Test Tube c: Light blue precipitate
- Test Tube d: Clear with white solid
- Test Tube e: Clear with white solid
Based on the observations, Test Tube d and Test Tube e have an excess of CuSO4.
2. To determine the test tubes with an excess of Na2S, you can follow the same logic as for Question 1. Look for no precipitation or little change in color, indicating an excess of Na2S. From the observations given:
- Test Tube a: Dark blue precipitate
- Test Tube b: Dark blue precipitate
- Test Tube c: Light blue precipitate
- Test Tube d: Clear with white solid
- Test Tube e: Clear with white solid
Based on the observations, none of the test tubes have an excess of Na2S.
3. To determine the test tube with the largest amount of precipitate, compare the masses of the test tubes. The test tube with the largest mass will have the most precipitate. From the data given:
- Test Tube a: Mass + ppt* = 18.210g
- Test Tube b: Mass + ppt* = 18.219g
- Test Tube c: Mass + ppt* = 18.229g
- Test Tube d: Mass + ppt* = 18.219g
- Test Tube e: Mass + ppt* = 18.210g
Based on the masses, Test Tube c has the largest amount of precipitate.
Explanation: Test Tube c has the largest amount of precipitate because it had an equal amount of CuSO4 (3 mL) and Na2S (3 mL). This indicates that both reactants were consumed in approximately equal amounts, suggesting that they were present in a 1:1 ratio, making them the limiting reactants. As a result, the maximum amount of precipitate (CuS) was formed.
4. The ratio of Cu+2 to S-2 can be determined by comparing the amount (in moles) of Cu+2 to the amount (in moles) of S-2 in the reaction. From the balanced chemical equation for the reaction:
CuSO4 + Na2S -> CuS + Na2SO4
The stoichiometry of the reaction tells us that 1 mole of CuSO4 reacts with 1 mole of Na2S to form 1 mole of CuS. Therefore, the ratio of Cu+2 to S-2 is 1:1.
5. The chemical formula of copper (II) sulfide is CuS. This can be determined from the balanced chemical equation for the reaction:
CuSO4 + Na2S -> CuS + Na2SO4
The formation of CuS as a precipitate confirms the presence of copper (II) ions (Cu+2) and sulfide ions (S-2) in the reaction, resulting in the formation of copper (II) sulfide.
Conclusion:
Based on the data and calculations, the hypothesis that the amount of product will be regulated by the limiting reactant is true. The observations and test tube analysis showed that Test Tube c had the largest amount of precipitate, indicating it had an equal amount of CuSO4 and Na2S. This suggests that they were the limiting reactants, and the maximum amount of precipitate (CuS) was formed. The ratios of Cu+2 to S-2 and the chemical formula of copper (II) sulfide were also determined. Overall, this lab reinforced the concept of limiting reactants and their impact on the amount of product formed in a chemical reaction. To improve the experiment, you could repeat the trials multiple times to ensure accuracy and consistency. Additionally, you could vary the concentrations of the reactants to investigate their effect on the amount of precipitate formed.