1748 words - 7 pages

Raj Nathwani

Chemistry 201

Laboratory 2: Density Measurement

Introduction:

The purpose of this laboratory exercise is to introduce basic laboratory measurements, with a specific emphasis on the units of mass and volume. Familiarization with measuring mass and volume, and calculating density from the results will also be executed. The overall goal of the laboratory is for the student to be able to draw conclusions on the relation between the position of metals on the periodic table and their respective densities. Density, or the degree of compactness of a substance, can be easily measured through the ratio of the mass of a substance divided by the volume of that substance. ...view middle of the document...

We measured the mass of six different metals, in six different forms, and then put these metals, one by one, into a graduated cylinder of water. The volume of the graduated cylinder before the metals were put in was defined by “initial volume”, and the volume of the graduated cylinder after the metals was put in was defined as “final volume.” The density could then be calculated through the net masses and net volumes of each metal. In the second exercise, we determined the density of two solids, iron chips and copper beads, by physically measuring the masses and measuring the volumes by direct measurement. Since the bead was essentially a cylinder, we calculated its volume through the volume of a cylinder formula. The same was done for the iron chips, but the volume of a triangular prism was utilized. Finally, we calculated the density of copper pennies in both ways; volume displacement and direct measurement. Out of the total 14 pennies, volume displacement was used for 12 of them, and direct measurement was used for the oldest and newest penny. From this data, we can understand the correlation between the densities of old and new pennies to the actual density of copper. Percent error was used for all three exercises to understand which technique was more accurate in calculating density; volume displacement or direct measurement.

Results:

For the first exercise, we used three significant figures, which gave the accurate calculations for density. The densities for volume displacement were pretty close to the actual volumes of the metals, accept for our measurement of the lead piece, which was 71.7% off. This can go down as human error, because something must have gone wrong when measuring the volume of the lead piece. The direct measurements of metals were off by 35.6% and 8.7%, which is expected since direct measurement of small substances is difficult to execute. The combined pennies, measured through volume displacement, were off of the density of copper by 15.7%, which is fairly close. Unsurprisingly, the newest penny’s density was off by only 2.1% compared to the actual density of copper. The explanation is that the lab group did an excellent job obtaining the dimensions of the newest penny, and that the newer penny is closer to being pure copper than the old penny.

Density = Net Mass/Net Volume

Volume of a Cylinder = height *π*radius2

Volume of a Triangular Prism = (1/2)*length*width*height

|Solid |Form |Method |Density |Percent Error |

|Copper |Bead |Volume Displacement |8.87 g/mL |1.0% |

|Copper |Wire/Plate |Volume Displacement |8.98 g/mL |.2% |

|Magnesium |Chip |Volume Displacement |1.79 g/mL |2.8% ...

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