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Density LabSample Lab ReportAaron KellerOctober 2007IntroductionDensity is an important property of substances and objects. It determines whether or not an object will float in water (or any other liquid). If the object’s density is higher than the liquid’s density, then it will sink. If the object’s density is lower, it floats. If it has the same density then it is neutrally buoyant and neither sinks nor floats.Density is defined as the ratio of the mass to volume. Mathematically this is written: D = m/V. The usual units for density in the lab are g/cm3. Because density is a ratio it is constant regardless of the amount of mass or volume. Another way to say this is to say that there is a direct proportion between mass and volume. That is, as mass increases, so does volume, and vice versa. Scientists calla property intensiveif it does not depend on how much material is present. Density is an intensive property which is a ratio of two extensive properties. The size of a mass or volume measurement depends on the amount of material present.Objectives1.To measure the density of cork, sand, mossy zinc, and glass marbles with the highest possible precision and accuracy.2.To measure the thickness of a piece of aluminum foil in an indirect fashion since it is too thin to measure with an ordinary ruler.Materialsmossy zinccorksglass marblessandaluminum foilcm rulergraduated cylinders (10, 50 mL)waterlab balanceProcedureWe used the following generalized procedure to find the density of the four substances. First, we used a lab balance to find the mass of a sample. Next, we filled a graduated cylinder partway with water, read the volume, and added the sample. By reading the volume of the water plus the sample, and subtracting the volume of the water alone we were able to measure the volume of the sample. The zinc in particular seemed particularly suited to this technique since the pieces of zinc were so irregularly shaped. Unfortunately, that irregularity may have led to inaccurate results since we could not be sure that all of the air bubbles had been knocked off of the zinc. Also, the zinc may have harbored air pockets which were impossible to see.Several samples of each substance were used in order to gauge the repeatability of our measurements. Multiple measurements of different amounts of each substance allowed us to
calculate the precision of our measurements and to graph the data to illustrate the direct proportion between volume and mass.We measured the length, width and mass of several pieces of aluminum foil. Before making our measurements we tried to make sure that the pieces of a foil were as rectangular as possible.DataThe following tables display the data collected.Table 1Mossy ZincVolume (mL)Mass (g)Density (g/mL)0.966.807.080.866.107.090.997.107.171.186.655.64average6.8range1.54±0.8Table 2SandVolume (mL)Mass (g)Density (g/mL)22.9037.011.6251.7080.401.567.6011.931.57average1.58range0.06±0.03Table 3MarblesVolume (mL)Mass (g)Density (g/mL)2.005.202.602.005.202.602.006.203.10average2.8range0.50±0.3Table 4CorkVolume (mL)Mass (g)Density (g/mL)5.001.100.225.001.100.220.590.100.1713.02.360.18average0.20range0.05±0.03Table 5Aluminum FoilL (cm)W (cm)A (cm2)m (g)volume (cm3)thickness (cm)25.6020.19516.93.351.242.4 x 10-318.9515.75298.52.010.7462.3 x 10-325.6521.32546.93.401.262.5 x 10-3average2.4 x 10-3AnalysisData concerning mossy zinc can be found in table 1. The average density measured for zinc is 6.8 ± 0.8 g/mL. Note that one value is quite far off from the other three. There is a large possibility that this data point is in error due to unseen air pockets in thezinc. The air pockets increased the apparent volume, which decreased the calculated density. If this data point is ignored the average density of zinc is found to be 7.12 ± 0.04 g/mL. This is much closer to the accepted value of 7.14 g/mL. This measurement shows high accuracy since it is close to the