Title: Density of Liquids Purpose: Find the density of tap water and how a property such as density be used to identify an unknown substance. Materials and Apparatus: chemical splash goggles; laboratory apron; laboratory balance; graduated cylinder (10-mL); 6 plastic micropipets; unknown liquid; tap water Drawings: Procedures and Observations: Procedures: First, put on the safety goggles and lab apron. After that, obtain the micropipets and label them1-6. Then place micropipette #1 on the lab balance and measure the mass to the nearest 0.01g. Record the data in Data Table 1. Fill #1 with tap water and measure its mass to the nearest 0.01g and record in Data Table 1. Then transfer the tap water from the micropipet into a graduated cylinder. After that, measure and record the volume to the nearest 0.1mL. Then repeat the above steps with micropipets #2 and #3 so that three sets of mass and volume are recorded in Data Table 1. After that, Obtain 50mL of an unknown liquid supplied from your instructor. Using micropipets #4, #5, and #6 repeat the above procedures and record the measurements in Data Table 2. Carefully dispose of all chemicals as instructed, clean up the work area, and wash your hands. Observations: The observations were that the measures for the unknown and the tap water were very similar in measurements. Data: Data Table 1 Trail 1 Trial 2 Trial 3 Mass of empty micropipette (g) 1.02 .98 .96 Mass of filled micropipette (g) 3.39 3.82 3.76 Mass of water (g) 2.37 2.84 2.80 Volume of water (mL) 2.2 2.6 2.5 Density of water (g/mL) 1.08 1.09 1.12 Unknown 1 Unknown 2 Unknown 3 Mass of empty micropipette (g) .98 .93 .95 Mass of filled micropipette (g) 3.90 3.61 3.40 Mass of unknown (g) 2.92 2.68 2.45 Volume of unknown (mL) 2.6 2.5 2.2 Density of unknown (g/mL) 1.12 1.07 1.11 Data Table 2 Conclusions: The results of Data Table 1 were very similar to the results of Data Table 2. It was concluded that the unknown was also tap water. Error Sources: There were no error sources. Questions: 1. Based on your data, which of the liquids in the table on the next page could be your unknown? Explain. TABLE 3 Densities of Some Liquids Liquid Density (g/mL) Ethanol 0.789 Isopropyl alcohol 0.786 Methanol 0.791 Corn oil 0.921-0.928 Water 0.998 Ethylene glycol 1.114 Glycerine 1.261 Based on the data in Table 3 the liquids that could be the unknown could be Water, Ethylene Glycol, or Glycerine because the density is very close to the average density of our unknown. 2. Could your unknown be a liquid that is not listed in the table in Question 1? Explain. The unknown could be a liquid that is not listed in the table in Question 1 because there are many other liquids in the world and the unknown could have a very different density than the liquids in the table. 3. Using the formula below, calculate the percent error for the average density of water that is determined in the investigation. Do the same for the average density of the unknown liquid. Your teacher will provide you with the accepted value for the density of each liquid. Percent error = (measured value – accepted value) divided by accepted value X 100 Percent error for density of water: 10% Percent error for density of unknown: 10% 4. Why do you think your measured values differ from the accepted density values for water and the unknown liquid? I think the results differed because the mass of the micropipets, water, and the unknown differed from the beginning which would differ the final result even more. 5. What changes could you make in the procedure to increase the accuracy of your results? The only change I would make is to use a different graduated cylinder every time the volume was measured because drops of water from the previous measurement could alter the results. 6. Look again at Table 3. If your unknown had a density of 0.79g/mL and you knew that it was one of the three substances listed in the table having a density close to your value, how would you go about determining which liquid was your unknown? An experiment could be conducted using those three liquids to find out what properties they have and then perform the same tests to the unknown liquid and the ones that the properties match are the same liquids. 7. Ice floats on water. Is ice more or less dense than water? How do you think the density of ice affects the survival of water-dwelling organisms in environments where temperatures fall below the freezing point? Ice is less dense than liquid water. I think it doesn’t really affect water-dwelling organisms because the water only freezes into ice on the top of the body of water and the liquid water stays flowing as usual. 8. When stating the density of a liquid, why is it necessary to state the temperature? It is necessary to state the temperature because there are different forms of many liquids that occur in different temperatures which changes the density. 9. The density of petroleum oil is less than the density of sea water. How would this property affect methods used to clean up an oil spill in the ocean? It would affect the methods to clean up the spill because since it is less dense then it won’t float and it will sink and spread throughout the ocean which makes it much more difficult to clean up. 10. Describe the procedures you would use to measure the densities of a solid and a gas. Explain how these procedures would differ from those used to determine the density of a liquid. To measure the density of a solid would be to get the mass by weighing it and then get the volume by putting it in a graduated cylinder with water and subtracting the volume of water. After that just divide. For the gas, put the gas into a container that the volume is known and then weigh the gas in that container and then just divide.