DENSITY MYSTERY



DENSITY

Density is a measure of how compact matter is. When you compare densities of two different materials, you are comparing the masses of the materials in a given volume. It is not practical to break off pieces of material with the same volume, so we use the mathematical relatioinship:

Density = D = mass divided by volume = M / V

In determining density, we measure mass in grams and volume in cm3 or milliliters, ml.

The table below gives the densities of 15 samples. Follow the procedure given below to determine the densities of 8 of the cylinders, and use the table below to identify the unknowns.

|SAMPLE |DENSITY |

|WALNUT |0.64 |

|OAK |0.75 |

|MAPLE |0.77 |

|POLYPROPYLENE |0.90 |

|POYETHYLENE (LDPE) |0.92 |

|POLYAMIDE (NYLON) |1.15 |

|ACRYLIC |1.17 |

|POLYURETHANE |1.23 |

|PHENOLIC |1.32 |

|POLYVINYLCHLORIDE (PVC) |1.37 |

|ACETYL |1.42 |

|PTFE (TEFLON) |2.2 |

|ALUMINUM |2.71 |

|BRASS |8.56 |

|COPPER |8.91 |

PROCEDURE:

1) Select a cylinder for testing, and record the letter on the cylinder in your table.

2) Use the electronic balance to determine the mass in grams of your cylinder. Make sure the balance is reading zero before you place the cylinder on the balance pan.

3) Add approximately 50 ml of water to your graduated cylinder. Make a note of the volume that you added. This is V1.

4) Gently add the cylinder that you are going to test to the graduated cylinder so that you do not splash water out.

5) Make sure the cylinder is completely under water. You may have to use the tip of a pencil to push the cylinder under. Note the volume of the water. This is V2.

6) The difference (V2 – V1) is the volume of the cylinder. Record this in our table.

7) Using the information that you now have. Calculate the density of the cylinder. Density = mass/volume

8) Use this density to find the identity of your cylinder. It should match the density of one of the materials in the table above.

|CYLINDER # |MASS |VOLUME |DENSITY |IDENTIFICATION |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

| | | | | |

CONCLUSIONS:

1. Is density a property that you could use to identify unknown materials? Discuss.

2. The density of water at room temperature is approximately 1 gm/ml. Which of the materials in the first table would float?

3. It is easier to float in salt water than it is in fresh water. Why?

4. What did you learn?

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download