Lab+1+Density

Title/Date: Density: A Characteristic Property 11/3/11

Purpose: The purpose of this lab is to investigate density as a means of identification of pure substances. For a given pure substance, the density will always be the same regardless of size.

List of Materials: Part A milligram balance 3 1 mL volumetric pipets pipet filler bulb vials with caps safety goggles hexane, acetone, and unknown liquid

Part B milligram balance 10 mL graduated cylinder small pieces of silicon, small pieces of tin, and water (tap or distilled)
 * Teacher Comment: Can list all materials together. **

Safety Considerations: You must wear safety goggles when handling the reagents.Also, make sure there are no open flames in the laboratory because organic liquids are flammable. Avoid breathing in the vapors of the liquids and make sure you work in a well ventilated work space. The liquids are toxic, so don't ingest them and make sure to wash your hands after handling the liquids. For the disposal of the liquids, they were safe enough to be poured down the drain. Make sure the vials are washed thoroughly with soap and water and are allowed time to completely dry berfore being used again. The pipets are to be washed the same way as the vials. For the solids, be sure to collect the solid pieces in a strainer to be dried. Make sure all of the pieces are out and dryy the graduated cylinder.

Data Table: partA
 * liquid:unknown || trial1 || trial2 || trial3 ||
 * mass of empty vial+cap || 26.658g || 26.580g || 26.477g ||
 * mass of vial+cap+liquid || 27.448g || 27.343g || 27.274g ||
 * mass of liquid || .790 g || .763 g || .797 g ||
 * volume of liquid || 1 mL || 1 mL || 1 mL ||
 * Teacher Comment: Limited yourself to one sig. fig. Volume should be 1.000 ml **
 * liquid:hexane || trial1 || trial2 || trial3 ||
 * mass of empty vial+cap || 26.497g || 26.664g || 26.542g ||
 * mass of vial +cap+liquid || 27.151g || 27.324g || 27.204g ||
 * mass of liquid || .654 g || .660 g || .662 g ||
 * volume of liquid || 1 mL || 1 mL || 1 mL ||

part B
 * liquid:acetone || trial1 || trial2 || trial3 ||
 * mass of empty vial +cap || 26.469g || 26.569g || 26.669g ||
 * mass of vial+cap+liquid || 27.248g || 27.342g || 27.446g ||
 * mass of liquid || .779 g || .773 g || .777 g ||
 * volume of liquid || 1 mL || 1 mL || 1 mL ||
 * solid:silicon || trial1 ||
 * mass of solid before added || 14.671g ||
 * volume of water || 6.2mL ||
 * volume after addition of solid || 7.2mL ||
 * volume of solid || 1.0mL ||
 * mass of solid after added || 12.279g ||
 * mass of solid || 2.3920g ||


 * solid:tin || trial1 ||
 * mass of solid before added || 23.936g ||
 * mass of solidafter addded || 21.160g ||
 * mass of solid || 2.7760g ||
 * volume of water || 6.3mL ||
 * volume after addition of solid || 7.2mL ||
 * volume of solid || 0.9mL ||

Questions/Problems: Pre-Lab 1) relative error = Iaccepted value-experimental valueI / accepted value RE= I.750 g/mL - .735 g/mLI / .750 g/mL RE= **.02 The relative error is .02.** 2) 1.55 g/cm3 + 3.51 g/cm3 = 5.06 g/cm3/2 = 2.53 g/cm3 RE = I2.63 g/cm3 - 2.53 g/cm3I / 2.63 g/cm3 RE= .0380 x 100 = **3.80 % The expected density of strontium is 2.53 g/cm3. The percent error is 3.80%.** 3) d = m/v d x v = m 2.63 g/cm3 x 1.00 cm3 = **2.63 g** (2.63 g / 1 cm3) x (100000 cm3 / 1 m) = **2.63 x 10^6 g The mass of exactly 1.00 cm3 of strontium is 2.63 g. The mass of 1.00 m3 of strontium is 2.63 x 10^6 g.** Density proves to be an intensive property because no matter the mass and volume, the density will always be the same for an element. 4a) (2.70 g / 1 cm3) x (1 lb / 453.6 g) x (2.54^3 cm3 / 1 in3) = **.0975 lb/ in3** (.997 g / 1 cm3) x (1 lb / 453.6 g) x (2.54^3 cm3 / 1 in3) = **.0360 lb/in3 The density of aluminum in lb/in3 is .0975 lb/in3 and the density of water is .0360 lb/in3.** b) specific gravity = density of substance/ density of water sp= .0975 lb/in3 / .0360 lb/in3 = 2.71 sp= 2.70 g/cm3 / .997 g/cm3 = 2.71 Therefore, because the two calculated specific gravities of aluminum are the same, the units of measurement for density does not matter.

Analysis 1) Acetone: Density = mass/ volume D = .779 g / 1 mL D of trial 1 = .779 g / mL D = .773 g / 1 mL D of trial 2 = .773 g / mL D = .777 g / 1 mL D of trial 3 = .777 g / mL mean density = (.779 g / mL + .773 g / mL + .777 g / mL) / 3 mean density = .776 g / mL Individual Deviation = average density - measured density ID = .776 g / mL - .779 g / mL ID trial 1 = .003 ID = .776 g/mL - .773 g/mL ID trial 2 = .003 ID = .776 g/mL - .777 g/mL ID trial 3 = .001 Average deviation = (.003 + .003 + .001) / 3 Average deviation = .002 2) 3) Acetone: percent uncertainty = (.002 / .776 g/mL) x 100 percent uncertainty of acetone = .258 % Hexane: percent uncertainty = (.003 / .659 g/mL) x 100 percent uncertainty of hexane = .455 % average percent uncertainty = (.258 % + .455 %) / 2 average percent uncertainty = .357 % Unknown uncertainty: (u / .783 g/mL) x 100 = .357 % u = .004 g/mL unknown uncertainty = .783 +/- .004 g/mL unknown is ethyl alcohol 4) Based on the density table, organic liquids with similar makeups have very close densities. For example, ethyl alcohol and 2- propanol are both alcohols, and their densities have a difference of just .001 g/mL. 5) Silicon: Density = mass / volume D = 2.392 g / 1 mL D = 2.392 g/mL % uncertainty = 1 mL / .02 mL % uncertainty = 20.0 % Tin: Density = 2.776 g/ .9 mL Density = 3.084 g/mL % uncertainty = .9 mL / .02 mL % uncertainty = 22.2 % 6) Density of germanium = (2.392 g/mL + 3.084 g/mL) / 2 Density of germanium = 2.738 g/mL percent range = (20.0 % + 22.2 %) / 2 percent range = 21.1 % The expected density of germanium is 2.738 g/mL with a 21.2 % range. 7) accepted density of germanium = 5.323 g/mL percentage error = (accepted - measured / accepted) x 100 percentage error = (5.323 g/mL - 2.738 g/mL / 5.323 g/mL) x 100 percentage error = 48.56% No, the accepted value does not fall within my uncertainty range. 8a) mean densities = (7.31 g/cm3 + 2.70 g/cm3) / 2 mean densities = 5.005 g/cm3 Mendeleev would predict the density of gallium to be 5.005 g/mL. b) percent error = (accepted- measured / accepted) x 100 percent error = (5.904 g/cm3 - 5.005 g/cm3 / 5.904 g/cm3) x 100 percent error = 15.23 % c) Gallium's density in it's liquid state is higher than when it is in it's solid state because of expansion during freezing. Since the accepted value for the density of gallium is measured around the melting point, some of the sample may be liquid, causing the density to be higher than if the entire sample was solid. Mendeleev's prediction was based on 20 degrees celcius, so gallium would be solid. Therefore, the prediction made by Mendeleev would have been larger if the temperature was at 29.6 degrees celcius.
 * Teacher Comment: Deviation has units **
 * liquid || trial1 || trial2 || trial3 || mean || Individual || devia || tion || average deviation ||
 * hexane || .654 g/mL || .660 g/mL || .662 g/mL || .659 g/mL || .005 || .001 || .003 || .003 ||
 * unknown || .790 g/mL || .763 g/mL || .797 g/mL || .783 g/mL || .00700 || .0200 || .0140 || .0137 ||
 * liquid || density+/- uncertainty || accepted density || Accurate? || Precise? ||
 * acetone || .776g/mL +/- .002 || .791 g/mL || no || yes ||
 * hexane || .659 g/mL +/- .003 || .659 g/mL || yes || yes ||

Analysis/ Summary: Thie calculations and results of this lab reveals that density can be found using the measured volume and mass of a given sample. With this experimental value, the identification of an unknown substance can be found. This experiment works as long as the results are accurate and little mistakes are made. The percent uncertainty should be under five percent. The results I got were too low and the uncertainty was too high to be very precise. With the calculated density of the unknown at .783 g/mL with an uncertainty of +/- .004, there are three possible given organic liquids that fit within the range, cyclohexane, ethyl alcohol, and 2-propanol. A source of error in part A could have been that the liquids evaporated during the experiment. This could have been prevented by putting on the caps faster to ensure none of the volatile liquids evaporated. Also, in part B, a source of error that could have happened was that after being removed from the graduated cylinder, the silicon and tin could have had droplets of water clinging to them at the time the were measured for mass. In order to prevent this from happening, I could have dried the pieces more thoroughly to ensure there was a more acurate mass reading.


 * Teacher Comment: Overall, not bad. A few minor mistakes. 47/50 **