Lab 3-Measurements II: Density Of A Solid Flashcards
What is the objective of this experiment?
The density of a metallic solid will be determined; however, the techniques will slightly differ from what was done in the first lab.
How will the volume of the metallic solid be determined?
Since solids rarely come in uniform shape (cube,cylinder), we will not measure the volume of the solid directly. Rather, we will determine the volume of water that is disc placed by the solid. This is a more accurate method that avoids any irregularities in the shape of the metal sample.
What is the procedure for this experiment?
Add approximately 200ml of distilled water to a beaker. While weighing the metal and flask in the following steps, be sure to periodically measure the temperature of the water. When it comes to a constant value, record the temperature in the notebook. This sample of water will be used for the rest of the experiment.
Obtain a metal sample and record the sample number. Weigh the metal to the nearest 0.001g.
Weigh a clean 25-mL Erlenmeyer Flask (with glass stopper) to the nearest 0.001g. Add some of the distilled water from the beaker to the 25-mL flask until the liquid level is even with the top. Carefully slide the stopper across the top of the flask until it is directly above the opening and then insert the stopper into the neck of the flask. This technique will avoid introducing air bubbles into the flask, but it may take a little bit of practice.
Once the stopper is securely seated, wipe the outside of the flask with a tissue to remove all moisture. Again, weigh the flask to the nearest 0.001g. From t he mass and temperature of the water contained in the flask, you can calculate the interior volume of the flask by using the data in Appendix H.
Pour out about half of the water and place the metal in the flask. Add additional distilled water from the beaker until the liquid level is even with the top of the flask. Use the technique described in the previous step to remove air bubbles and insert the stopper. Wipe any moisture from the exterior oof the flask and reweigh it. The new mass, together with the data you previously calculated will allow you to calculate the volume occupied by the metal.
You will repeat the above procedure three more times in order to obtain 3 values with at least 1% precision.
Dry the metal, flask, and stopper after each trial and before returning them.
Calculate the average density and standard deviation for the 3 closest trials. Be sure to report your results in the proper number of significant figures. (Appendix E)
Consult the Handbook of Chemistry and Physics (as shown in the science library orientation module) for densities of the metallic elements. From the average density value (+/- the standard deviation) you determine your “unknown” metal, suggest its identity (chemical symbol and name). If more than one element has a density within the measured range, include all possible metals. For example, if the density you measured in the lab is 8.842+/- 0.022, your unknown is most likely Cobalt (Co), the metal with the closest density.
