Metric System – Conversion Practice



Earth Systems Science LabCalculating the Average Density of Planet EarthIntroduction: Density differences in air, water and Earth’s lithosphere play a role in weather, ocean currents and plate tectonics. Different minerals have different known density ranges, which can be used to help identify them. Density of minerals is also referred to as “specific gravity.” For this lab you will be finding the density of six different minerals using a water displacement method to determine volume. You will then find the mass and calculate the density of each specimen. You will use what you find out to identify each sample. Remember that the formula for density is D = M / V. Materials:Graduated Cylinder 100 mlElectronic balanceWater6 mineral specimensPart One:On page one of your lab report: Include the lab title, your name and your partner’s name, then draw and label the lab materials On page two of your lab report: Write your procedures and the formulas you need to use (read these instructions first, and then summarize the steps for the lab). On page three of your lab report: Set up a data table like the one below on your lab report to record your data. Create one row for each of the six rock samples you will use (total of SEVEN horizontal rows!)Mineral NameMineral IllustrationMass in gramsInitial Volume in mL OR cm3Final Volume in mL OR cm3Write the name of the mineral in the first box.Draw an illustration of each sample in the second box. Please use color!Determine the mass of each sample using the electronic balance and record in the third column.To determine the volume of each sample in milliliters (mL), fill your graduated cylinder with approximately 50 mL of water. Record this volume in column four.Carefully lower each mineral sample into the graduated cylinder until it is under water. Record the second volume in the correct column. Because one mL of water is equal to 1 cm3, you can interchange the units so that your volume is in cm3. Since these minerals are solids, cm3 is more appropriate than mL for volume. Calculate the amount of water displaced which the volume of the sample. Subtract the initial volume from the final volume. For example, if you start with 50 mL of water and after you lower the sample into the cylinder the new volume reads 65mL, then the volume of the sample is 15mL. Make a Calculations table (seven horizontal rows) and place this in the second column.Calculate the density using the formula d = m/v. Record this value in the data table in the third column. Call a teacher over to check your work.Mineral NameVolume in mL OR cm3Density (d=m/v)IdentificationThe known (expected) densities of the minerals that these could be are:Gypsum – 2.36g/cm3Quartz – 2.652g/cm3 Calcite – 2.71g/cm3 Fluorite – 3.13g/cm3Iron Pyrite –5.022g/cm3 Hematite – 5.262g/cm3Determine which type of mineral that each sample is according to its density and write its name in the far right column on your lab report. Below the data table, calculate the average density of all your mineral samples combined (add all densities, divide by 6). Label this as the “Average density of rock”We learned in our lab last week that the average density of rock is 3.5 g/cm3. How close did you come?Part Two:Background Information: The Earth is approximately one-third iron, which has an average density of 7.87 g/cm3. Our planet’s core is made up of iron and nickel and extremely dense while the lithosphere (crust) is the least dense. The minerals you used in Part 1 are just a few of those found on Earth’s crust. Now you will use the data you gathered for the density of the rock samples, together with the known average density of Iron, to estimate the average density of the Earth and see how close you came to finding the Earth’s actual average density.4. On the top of page four of your lab report: Record the average density of your mineral samples, from where you wrote it on page three. 5. Add the average density of iron (7.87 g/cm3) to the average density of YOUR samples and divide by two (2) to find a combined average. Label this as your ESTIMATED average density of the Earth.6. The actual average density of the Earth is 5.52 g/cm3 (its expected value). To compare the actual density of Earth to your experimental or observed value, calculate the percent of error using the formula: % Error = [(experimental – expected) / Expected] x 100OR: % Error = [(experimental – 5.52 g/cm3) / 5.52 g/cm3] x 100Write this formula on your paper, under your ESTIMATED density of Earth, plug in your estimated density and solve to find out YOUR percent error. Label the results as your percent of error.7. Draw some conclusions about your results. Answer these questions on the bottom of page four of your lab report. How close are you? The group that gets the closest gets a sweet surprise! Which mineral had the highest density? Which had the lowest? Why do you think different minerals have such different densities?What layer of the earth do the rock samples represent (crust or core)? The iron?Explain why percent of error is about variation and not about being wrong.Turn in your completed lab report! ................
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