1. to Make a Number of Metric Measurements, Reading Each Instrument with Proper Precision

DENSITY LAB Name______Date_____ Period____ Purpose 1. To make a number of metric measurements, reading each instrument with proper precision. 2. To determine the density of liquids, regularly shaped, and irregularly shaped solid samples. 3. To calculate the error in the data, and compare results to “Literature Values”. Background Ever hear people complain about the fact that they have been working out for months but weigh more than they did when they started? Ever hear people say “muscle weighs more than fat”? This has to do with the fact that muscle tissue is more dense that fat tissue. Thus, one pound of muscle tissue will occupy less space than one pound of fat tissue. The density of an object relates the ratio of it’s mass (the amount of matter the object contains) to it’s volume (the amount of space the object occupies.). This can be expressed by the equation:

Mass Density = Volume

Measurement of mass is as simple as using a balance. Measurement of volume may be done a few different ways. If the sample is of a geometric shape that you know a simple formula to calculate volume from, you can just measure the dimensions and calculate volume using the formula. Another possible method is Archimedes principle of water displacement, which states that the volume of an object completely submerged in water will be equal to the amount of water displaced by the object.

PART 1 – The density of liquids - water and ethanol Procedure: USE SEPARATE, LABELED, GRADUATED CYLINDERS TO MEASURE LIQUID SAMPLES A. Create DATE TABLE 1 to record your measurements for Part 1. Be sure you record the correct number of significant digits in your measurements. B. Density of Water (distilled) 1. Put approximately _____ ml of water into a 50 mL graduated cylinder. 2. Record the volume of water. 3. Place a 100 mL beaker on the balance, “tare” the balance, and pour the water sample into the beaker. 4. Record the mass of the water sample. C. Density of Ethanol 1. Repeat the above procedure using ethanol instead of water.

PART 2 – The density of a geometric solid 1. Create Data Table 2 for measurements of Part 2. 2. Record the identity of your solid sample. Be sure to use the same substance for Part 3 (i.e. use copper for BOTH parts 2 and 3) 3. Measure the mass of your solid sample 4. Measure the dimensions of your solid sample (length, width, height, and possibly diameter)

1 PART 3 – The density of an irregular solid 1. Create a Data Table 3 for measurements from Part 3. 2. Measure the mass of the dry metal “shot” in a beaker. 3. Put about 25 ml of tap water in a 100 ml graduated cylinder. Record the precise volume. 4. Add the metal shot to the water, pouring slowly to avoid air bubbles. Record the volume of the water and metal. 5. Drain off the water and spread the metal on a paper towel to dry.

MAKE YOUR OWN DATA TABLES IN SPACE BELOW (IF YOU WISH)

2 Calculations You may find these equations helpful – make sure your answers are rounded properly for significant figures.

Volume of a cube = l x w x h Volume of cylinder = r2 x h

1. Calculate the density of your water and your ethanol sample. Water ______g/mL

Ethanol ______g/mL

2. Calculate the density of your geometric solid sample. ______g/mL

3. Calculate the density of your irregular solid sample. ______g/mL

ERROR ANALYSIS 4. Finally, look up the accepted (literature) value for the density of your metal and calculate the percent error for each sample.

Name of metal: ______Literature density value: ______

|experimental - theoretical| % error =  100 theoretical

5. Percent error for Part 2 (geometric solid) ______

6. Percent error for Part 3(irregular solid) ______

GRAPHICAL ANALYSIS

7. Using the class data, plot a graph relating mass and volume for BOTH the water and the Ethanol samples. Plot mass on the vertical axis and volume on the horizontal axis. Choose a scale that will generate a graph that fits comfortably on the full graph paper. Decide whether the point (0,0) should be included in the graph. (When volume is zero, will mass be zero?)

8. Use a ruler to draw the best straight line through the plotted set of points for each curve. Note that not all of the points will lie on the best straight line. Therefore, the line should be drawn so that approximately half of the points lie above the line and half the points lie below the line.

9. Determine the slope of the lines from your graph. What does the slope represent?

Slope of Water graph ______Slope of Ethanol graph ______

3 Questions

1. Do you think density can be used to identify a substance? Explain your answer.

2. Did the density of your metal depend upon the size of the sample?

3. What kind of information do error calculations give you?

4. What type of samples is it necessary to use Archemedes principal to calculate volume, AND why?

5. How would you go about determining the density of table salt. (Be careful! Some of the techniques used in this lab may be appropriate, but others are not.)

6. If you were able to see the arrangement of the atoms that make up copper and aluminum, with densities of ______and ______respectively, how would you think they differed? Draw me a picture!