To determine what is wrong with the student's result, we need to compare the experimental data with the expected theoretical values. Let's calculate the theoretical values first.
1. Calculate the molar mass of copper sulfate pentahydrate (CuSO4路5H2O):
- Molar mass of CuSO4: 63.55 g/mol (copper: 63.55 g/mol, sulfur: 32.07 g/mol, oxygen: 16.00 g/mol, 4 oxygens in the formula)
- Molar mass of 5H2O: 90.10 g/mol (5 moles of water, each with a molar mass of 18.02 g/mol)
- Total molar mass = 249.68 g/mol (CuSO4: 159.61 g/mol + 5H2O: 90.10 g/mol)
2. Calculate the expected mass of copper sulfate pentahydrate (CuSO4路5H2O) using the molar mass from step 1:
- Mass = moles * molar mass
- Moles of CuSO4路5H2O = mass / molar mass = 2.146 g / 249.68 g/mol
Now, let's calculate the expected mass of salicylic acid (C7H6O3):
1. Calculate the molar mass of salicylic acid (C7H6O3):
- Molar mass of C7H6O3 = 138.12 g/mol (carbon: 12.01 g/mol, hydrogen: 1.01 g/mol, oxygen: 16.00 g/mol, 7 carbons, 6 hydrogens, 3 oxygens)
2. Calculate the expected mass of salicylic acid using the molar mass from step 1:
- Mass = moles * molar mass
- Moles of C7H6O3 = mass / molar mass = 3.094 g / 138.12 g/mol
Now let's compare the calculated theoretical values with the experimental data:
- The expected mass of CuSO4路5H2O is obtained by multiplying the moles of CuSO4路5H2O by its molar mass (2.146 g / 249.68 g/mol). Compare this with the experimental mass of 2.146 g. If they are not equal, it indicates a difference between the expected and experimental values.
- The expected mass of salicylic acid is obtained by multiplying the moles of salicylic acid by its molar mass (3.094 g / 138.12 g/mol). Compare this with the experimental mass of 3.094 g. If they are not equal, it indicates a difference between the expected and experimental values.
Based on the calculations, we can determine what might be wrong and how the error could have been avoided:
1. Theoretical calculations: Validate that the theoretical calculations done to determine the expected masses are correct. Check the molar masses, the stoichiometry of the reaction, and the calculations for determining the theoretical masses.
2. Experimental techniques: Ensure that the measurements and procedures followed by the student during the experiment were accurate. Check for any potential sources of error, such as spillage, incomplete reactions, or losses during the process of recovering the substances.
To avoid such errors:
- Be careful and precise when measuring substances during the experiment.
- Use analytical balances with a higher precision to get more accurate mass measurements.
- Refine the experimental technique by repeating multiple trials to account for any unforeseen variations and improve the accuracy of the results.
By following these precautions, the student can minimize errors and improve the accuracy of their experimental results.