Densities of Liquids, Significant Figures, and Graph Interpretation
Objective: Properly use Sig. Figs. in density calculations, and plot a graph of the data.

Materials: alcohol, water, ethylene glycol, graduated cylinders, balance
Note: Use of Sig. Figs. in measurements and calculations is required.

Methods
1. Mass a 50.0 mL or 100 mL graduated cylinder.
2. Add approximately 10 mL of liquid A, then determine the mass of the liquid by subtracting the cylinder’s mass.
[Note: volumes can vary, but must be known exactly to 0.1 mL]
3. Add 10 mL more of the same liquid; mass again. Repeat up to a total of 50 mL or slightly less.
4. Clean your graduated cylinder, then dry it.
5. Repeat Steps 1 - 4 for the two other liquids.
6. Determine the mass and the area of the aluminum foil sheet at your lab station.

Analysis
1. Plot the mass (y axis) vs. volume (x axis) for all liquids. Draw a best fit straight line for each.
2. Calculate the density of each liquid using the liquid's total mass at the maximum volume.
3. Calculate the slope of each line. What does the slope represent and what are the units?
4. Estimate by interpolation the mass of each liquid at 16.0 mL, 27.0 mL, and 44.0 mL. Write an equation for the graph of the line. (Hint: y = mx + b)
5. Which measurement was limiting in accuracy, mass or volume. Explain.
6. Define the term interpolation. Can you justify extrapolation on this graph? Explain.
7. Why can the water measurements be used as an indicator of your accuracy and precision?
8. The density of aluminum is 2.7 g/cm³. Determine the thickness of the aluminum foil sheet on your lab table.

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