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| *Please ignore the writing on the page - they are just my personal notes |
Title: Plastic Determination by Titration
Purpose: To determine the density of a plastic sample (barrel of Bic Round Stic2) by titration and ethanol displacement.
Data:
Observation - The plastic floats in water and sinks in ethanol.
Mass of beaker (g)
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50.23
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Volume of ethanol in buret (mL)
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32.5
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Volume of water in buret (mL)
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37.0
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Starting volume of ethanol in beaker (mL)
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15.00
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Mass of beaker + ethanol (g)
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62.02
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Volume of water in buret after titration (mL)
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25.00
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Volume of water use for titration (mL)
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12.00
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Volume of remaining plastic (mL)
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1.45
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Mass of remaining plastic (g)
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1.42
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Volume of ethanol + water solution (mL)
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24.50
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Calculated density of Bic barrel by titration (g/mL)
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0.971
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Calculated density of Bic barrel by displacement (g/mL)
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0.979
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Accepted density of ethanol (g/mL)
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0.789
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Percent error for ethanol density (%)
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0.380
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Accepted density of water (g/mL)
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1.00
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Percent error for water density (%)
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0.00
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Accepted value for Bic Rounc Stic2 plastic barrel (g/mL)
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0.903
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Percent error for plastic density: titration (%)
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7.53
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Percent error for plastic density: displacement (%)
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8.42
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Calculations:
1.) Calculate the density of the two liquids from the Procedure A data.
Density = mass/volume
a.) Mass of ethanol = beaker + ethanol - beaker
= 62.02 - 50.23
= 11.79 g
Density of ethanol = 11.79 g/15.00 mL
= 0.786 g/mL
b.) Density of water = 12.0 g used for titration/12.0 mL used for titration
= 1.00 g/mL
2.) Calculate the mass of both liquids in the titration using the densities obtained in Procedure A. Add the masses of water and ethanol to determine the solution's mass at the end point.
Mass = density x volume
a.) Mass of ethanol = 0.786 g/mL(15.00 mL) = 11.79 g
b.) Mass of water = 1.00 g/mL(12.0 mL) = 12.0 g
c.) Solution mass at end point = 11.79 + 12.0 = 23.79 g
3.) Calculate the density of the plastic by using the solution's mass and volume. At the end point, the solution's density is equivalent to that of the plastic.
Density of solution = Density of plastic
Density of solution/plastic = 23.79 g/24.50 mL = 0.971 g/mL
4.) Calculate the percentage of volume reduction of the titrated solution.
[- (Buret: water + Buret: ethanol) + (graduated cylinder)]/(Buret: water + Buret: ethanol)
= [24.50 - (12.0 + 15.00)]/(12.0 + 15.00)
= 9.26%
*this would be mathematically negative, but percentages usually ask for percent of change regardless of the direction which can be assumed from the sign of the value
5.) Calculate the plastic density again, this time using the barrel mass and volume displacement of ethanol obtained in Procedure C.
Density = mass of remaining plastic/volume of remaining plastic
= 1.42 g/1.45 mL
= 0.979 g/mL
6.) Calculate percentage of error for the densities of water and ethanol. Calculate the percentage of error for the density of plastic determined by both titration and ethanol displacement.
[(Experimental - Accepted)/Accepted] x 100 = Percent error
a.) Ethanol density percent error
[(0.786 - 0.789)/0.789] x 100 = 0.380%
*mathematically negative, but percent errors are always positive, as the sign simply indicates direction
b.) Water density percent error
[(1.00 - 1.00)/1.00] x 100 = 0.00%
c.) Titration method: plastic density percent error
[(0.971 - 0.903)/0.903] x 100 = 7.53%
d.) Displacement method: plastic density percent error
[(0.979 - 0.903)/0.903] x 100 = 8.42%
Procedure:
Obtain Bic Round Stic plastic barrels, ethanol, distilled water, and glass burets (must be glass). Take proper safety precautions and wear a lab apron and goggles before handling the materials, Measure out about 50 mL of distilled water and 30 mL of ethanol into two separate glass burets using funnels. Make sure that the faucets on both burets are closed (perpendicular). Mass a beaker and run 15.00 mL of ethanol into it; then mass the beaker and ethanol. Obtain the two pieces of Bic pen barrel - one measuring ~3 cm and the other remaining piece. Drop the small piece into the ethanol beaker and observe that the piece sinks (it floats in the water). Record the beginning volume of water in the buret and while swirling, titrate the ethanol solution with water until the plastic floats in the middle of the water and ethanol layers. Record the buret reading. Mass the remaining pen barrel and record the new volume after the piece is dropped into ethanol. Dispose of the waste properly and clean the lab station and equipment.
Conclusion:
By using two miscible solutions of different densities, the density of a solid, in this case a Bic Round Stic pen barrel made of plastic, was able to be experimentally determined using both the titration and ethanol displacement methods. Water, more dense than both the ethanol and the plastic barrel, was used to change the density of the solution to the point where the barrel floated. In both methods, ethanol displacement and titration, through volumetric analysis, the data was both precise and accurate at the D = 0.971 g/mL and D = 0.979 g/mL respectively. Though the slight deviation from the expected 0.903 g/mL exists, it can be explained by the systematic error of a small air bubble at the tip of the buret as well as the random errors in volumetric and mass measurements and in system contamination. Density reveals significant information as to physical properties of certain substances in relation to others and in the aforementioned methods, both were successful in using relative fluid densities to determine an unknown density.
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Disclaimer: I do not own any of the above materials associated with the published lab and I do not encourage copying verbatim my answers for honesty sake and for the sake of risking your grade should others choose to copy also. While I do not own the lab materials, the work is my original work that I have typed from my laboratory notebook.
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