Post-Lab Questions

Directions:

Answer the following questions, show work for all calculations. Work must be shown to receive credit for calculations. All questions are weighted equally.

1. If copper is known to have a density of 8.92 g/cm³, determine the percent error & standard deviation of the class data set. Is the class data set accurate, precise, both, or neither?
2. Using a sheet of graph paper, draw a full-page bar graph displaying each of the experimental copper density values from the class data set. (Alternatively, use a spreadsheet program to plot this graph). Be sure your graph contains: Graph title, axis titles, and appropriate units.
3. Two methods can be used to determine the volume of an object: geometric calculations and water displacement. Did the density values you calculated for the copper cylinder differ between the two methods? Which method produced the more accurate density value? Use your experimental data to support your answer.
4. Explain how you chose the identification of your unknown solid. What is the significance of density in identifying unknown materials?
5. For the unknown metal, did your experimental density differ from the theoretical density listed in the box? Identify 2 potential experimental sources of error. You may address errors in either method – geometric calculations or water displacement.

Note: When explaining sources of error, avoid vague terms like “human error” or “experimental error” — instead, be specific about what happened. Errors in calculations or significant figures don’t count because they can be checked and fixed before submitting your report. Don’t list general balance calibration issues, since the equipment is regularly maintained.  Focus on experimental factors during the lab that clearly affected your results.