The purpose of this lab is to calculate density. Density is the ratio of a substance's mass
Question:
The purpose of this lab is to calculate density. Density is the ratio of a substance's mass to its volume. Density is an intrinsic or characteristic property of matter in that any given amount of the same pure or homogeneous substance will have the same density. Other characteristic properties include solubility, conductivity, and malleability. Density is also known as a physical property in that it can be measured without changing the substance. This is opposed to a chemical property, for example flammability or reactivity, which do change the substance.
As a characteristic physical property, density can be used to identify an unknown sample of a pure substance. There are many ways to calculate density including a hydrometer, a spring scale, a pan balance or through volumetric displacement using a graduated cylinder. Archimedes of Syracuse is credited with having discovered the volumetric displacement method for determining density when he had to determine whether a temple offering had been made of pure gold or of some alloy (Vitruvius 2010). The equation for density is:
ρ = m (1)
v
In Eq. 1, and using SI units, density, symbolized by the Greek letter Rho, ρ, is mass, m, in kilograms (kg) divided by volume, v, in cubic meters (m3). Since pressure and temperature affects density, measurements should be carried out at Standard Temperature and Pressure (STP) (273.15 K and 100.00 kPA). For example, at STP, one 1.00 m3 of Cu has a mass of 8.94 kg and hence has a density of 8.94 kg/m3.
Experimental error can be calculated using Eq. 2:
% error = |experimental value - theoretical value| . 100
theoretical value (2)
In Eq 2, experimental error would be the absolute value of measured density (kg/m3) as found in the experiment subtracted from the theoretical density (kg/m3) value as shown in the periodic table divided the theoretical density (kg/m3) and multiplied by 100 in order to have a percentage.
That means, if the experimental density of Cu was found to be 8.71 kg/m3, then the experimental error would be:
2.57 % error = |8.71 - 8.94| . 100
8.94
It was hypothesized that samples of Al, Cu and Sn could identified after their densities had been determined through volumetric displacement in a solvent and the resulting values compared to a table of known densities.
MATERIALS
- samples of Al, Cu and Sn
- 3, 100 mL graduated cylinders
- distilled water
- Mettler Toledo PM4600 digital balance
PROCEDURE
INCLUDE PROCEDURE AND INSERT IT HERE.
RESULTS
Table 1: Measurements | |||
Unknown | Mass (g) | Volume-Initial (mL) | Volume-Final (mL) |
Unknown 1 |
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Unknown 2 |
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Unknown 3 |
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ANALYSIS
The volume of each unknown was calculated by subtracting the initial volume of water in each graduated cylinder from the final volume of water in each graduated cylinder after the unknowns were added (Table 2). The density of each unknown was calculated using Eq. 1. For example, for unknown 1, the calculation was:
SHOW WORK FOR UNKNOWN 1
The same process was repeated for unknowns 2, and 3 and the densities of all 3 unknowns were recorded (Table 2).
Table 2: Densities of unknown metallic solids. | |||
Unknown | Volume (mL) | Mass (g) | Density (g/mL) |
1 |
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2 |
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3 |
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Experimental densities were then compared to standard densities for the 10 listed unknowns from the Merck Index and the identities of the unknowns proposed (Table III). Error was calculated using Eq. 2:
For example, for unknown 1, the calculation was:
SHOW WORK FOR UNKNOWN 1
The same process was repeated for unknowns 2, 3, and the percentage errors were recorded (Table 3).
Table 3: Proposed identities of unknowns and percentage error. | ||||
Unknown | Proposed Identity | Experimental Density (g/mL) | Standard Density (g/mL) | Error (%) |
1 |
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2 |
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3 |
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DISCUSSION
Unknown 1 was ANSWER. Unknown 2 was ANSWER. Unknown 3 was ANSWER. The experimental results had a percentage of error between LOW VALUE and HIGH VALUE. Although there were many potential sources of error, the reproducibility of the digital balance and the accuracy of the graduated cylinders should be examined. The Mettler Toledo PM4600 digital balance has a reproducibility of +/1 VALUE. The 100 mL Class A graduate cylinder has an accuracy of +/- VALUE. It is thought that the reproducibility of the measurements on the digital balance and the accuracy of the glassware WOULD OR WOULD NOT have an effect on the identification of the unknowns. The reason why is __________.
CONCLUSIONS:
Through the volumetric displacement method of calculating density, it was determined that unknowns 1, 2, and 3 were ____.
Intermediate accounting
ISBN: 978-0077647094
7th edition
Authors: J. David Spiceland, James Sepe, Mark Nelson