9/26/13
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An Introduction to Calculating Density

Introduction:
Purpose: To determine the density of different substances using mass and volume measurements that have been calculated. Also, to familiarize oneself with the materials in the laboratory and to investigate the precision of measurements using precision of error. Hypothesis: If the density of a solid and of a liquid is calculated then the solid will be denser than the liquid.
Theory: This experiment involves analyzing quantitative data that has been measured. Significant figures were calculated in order to show the precision of the experiment. Also, students compared two densities together by finding the measurements of the mass and volume. The equation for calculating density is mass divided by the volume. Density itself is the quantity or mass of an object in a given space (volume). Mass is the amount of matter in an object and volume is the amount of space it occupies. This lab looks at density of water, alcohol (ethanol), and a metal (copper). Percent error is used to calculate how precise and instrument is. The accepted value is subtracted from the experimental value and then divided by the accepted value. The smaller the number the more precise. A negative indicates less than the value and positive is over the value.
Variables: The independent variable is the volume of the liquid. The dependent variable is the mass that is changing with the volume. For the metals it is actually the opposite. The independent variable is the mass with the metal, so therefore the dependent variable is volume of the liquid in the cylinder. The controlled variables are the scale and the significant figures, the room temperature, the size of beakers testing.
Materials and Methods:
List of Materials:
3 graduated cylinders: 10mL, 25 mL, and 50mL
1 balance to the 0.01 precision
Alcohol- Ethanol
Distilled Water- faucet may be used as well
A metal, copper was used
1 apron
Procedure:
1. The materials were gathered and set up.
2. The students put on aprons and goggles.
3. Next, the mass of a 10mL graduated cylinder measured and recorded to the nearest 0.01g. This was repeated for 25mL and 50mL cylinders.
4. The student carefully poured water into the graduated cylinder and proceeded to measure and record the newly calculated mass. This was repeated for all three-size cylinders.
5. The student read the volume on the cylinder at eye level and recorded it. Then the student also calculated the mass of the water by subtracting the mass of the cylinder from the mass of the cylinder and water combined. Finally, the student used the given formula to calculate the density and it was recorded.
6. The masses of the 10mL, 25mL, and 50mL cylinders were measured and recorded again.
7. Then, instead of water the student poured ethanol into the cylinders and calculated the mass once again.
8. The volume was read at eye level and recorded and the ethanol’s mass was calculated as well. The density was finally calculated.
9. After that experiment, the density of a metal was performed. The student put a small amount of copper into a 25mL cylinder that was filled with water and measured it. *The student measured the mass of the cylinder with water previously to this step. *
10. Then more copper was added to the graduated cylinder. The amount may vary as in the experiment enough copper was added to deflect the volume. Once again this was measured and recorded. This step was repeated again for a 3rd trial.
11. The mass of the metal itself was calculated as well as the volume, which was read. Finally, the density was once again calculated for each trial.
12. The students cleaned up the materials and the area.
Results:
Qualitative Observations: The water and the ethanol had air bubbles when they were first poured, but in general it was a