Determination of Density of Solids and Liquids

Objectives

• To determine the density of a sample of a liquid, a single solid object, and a collection of irregularly shaped solid objects.
• Familiarization with the laboratory: working in the lab
• Measurements, precision, experimental error, and significant figures.

I. Determining the Density of a Rubbing Alcohol Solution

1. Obtain a 10 mL graduated cylinder.
2. Record the limits of error for your graduated cylinder (±0.1 mL for the shorter, wider ones or ±0.02 mL for the taller thinner ones).
3. Wipe the outside of the graduated cylinder carefully with a cloth towel. From this point, the cylinder is not to be handled with your bare hands (eliminating a source of systematic error).
4. Place the graduated cylinder on the balance pan and obtain the mass.
5. Pour 5 to 6 mL of rubbing alcohol (Sample #1) into the graduated cylinder. Carefully read the volume to the limits of error of your graduated cylinder (figure 1). Avoid parallax! (figure 2)
6. Place the graduated cylinder containing Sample #1 on the balance, obtaining the combined mass of the alcohol sample and cylinder.
7. Pour the alcohol into a test tube. Obtain Sample #2 by pouring 4 to 5 mL of the alcohol back into the graduated cylinder. Carefully obtain the volume of Sample #2.
8. Obtain the mass of Sample #2 (obtain the combined mass of graduated cylinder and sample).
9. Discard alcohol into the appropriate waste container.

II. Determining the Density of a Rubber Stopper

1. Obtain a rubber stopper and record the number on the top of the stopper.
2. Thoroughly wipe the outside of the stopper, cleaning away dust, dirt, or oil, and dry it.
3. Weigh the stopper.
4. Place 50 to 60 mL of distilled water into your graduated cylinder, reading (estimating) the volume to ±0.2 mL. Record the volume.
5. Carefully slide the stopper down the inside of the tilted cylinder.
6. Read the volume of the liquid in the cylinder to ±0.2 mL.

III. Determining the Density of an Unknown Metal

1. Obtain a test tube containing a metal sample. The sample will consist of many small pieces. Use all of the test tube's contents for your determination.
2. Obtain a small, clean (dry) beaker. Place the beaker on the balance and press the tare function. Add the metal pieces to the beaker, obtaining the mass of the metal sample.
3. Place 50 to 60 mL of distilled water in your 100-mL graduated cylinder. Read (i.e. estimate) the volume to ±0.2 mL. Record the volume.
4. Tilt the graduated cylinder and carefully pour the sample down the inside surface of the cylinder avoiding splashing water. Hold the cylinder tightly and then either tap or swirl to dislodge trapped air bubbles.
5. Read the volume of the liquid in the cylinder to ±0.2 mL. Record the volume.
6. Carefully drain the water from the cylinder, avoiding the loss of metal pieces.
7. DO NOT RETURN THE WET METAL TO THE TEST TUBE!!
   Place your metal sample on a paper towel under one of the fume hoods. Replace the cork stopper in the test tube and place the test tube beside the metal sample.