Design and carry out an experiment to determine the density of the plastic object you have been give — Density and Experimental Design Chemistry Question
Problem Context
Design and carry out an experiment to determine the density of the plastic object you have been given. You may use water and the alcohol solution provided at your lab station, as well as the equipment you will find there, but you may not use a balance. You will be asked to describe the method you developed to solve this problem.
Given:
density of water = 1.00 g·mL–1
density of alcohol solution = 0.85 g·mL–1
Give a brief description of your experimental plan.
Model Answer
Either of two general plans might be used to solve this problem. Multiple trials are expected for either plan used.
Plan A: Make a solution of water and alcohol in which the object is suspended. Using the measured volumes of the water and alcohol, and their given densities, the density of the solution can be found. The density of the solution and the object will be the same.
Plan B: Using Archimedes’ principle, determine the volume of the object by displacing the alcohol. Determine the mass of the object by displacing water, and multiplying the volume of the water displaced by the density of water. Determine the density of the object by dividing the mass of the object by its volume.
Record your data and other observations.
Model Answer
Plan A Sample Data: Trial #1 Trial #2
Volume water to suspend object 2.21 mL 2.23 mL
Volume alcohol to suspend object 3.02 mL 3.03 mL
Plan B Sample Data: Trial #1 Trial #2
Initial volume water 5.02 mL 5.14 mL
Final volume water 5.83 mL 5.94 mL
Initial volume alcohol 6.01 mL 6.02 mL
Final volume alcohol 6.88 mL 6.89 mL
What is the density of the plastic object? Show your methods clearly.
Model Answer
Plan A Calculations:
Mass of solution = V_H2O × density_H2O + V_alcohol × density_alcohol
Volume of solution = V_H2O + V_alcohol (assuming volumes are additive)
Plan A Sample Results: Trial #1 Trial #2
Mass of solution (g) 4.78 4.81
Volume of solution (mL) 5.23 5.26
Density of solution (g/mL) 0.91 0.91
Plan B Calculations:
Mass of object = V_H2O displaced × density_H2O
Plan B Sample Results: Trial #1 Trial #2
Mass of object (g) 0.81 0.80
Volume of object (mL) 0.87 0.87
Density of object (g/mL) 0.93 0.92
Conclusion: The determined density should be between 0.85 g/mL and 1.00 g/mL, because the object sinks in alcohol and floats in water. The density determination must be supported by data gathered and calculations performed.