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Name KEY IB Chemistry SL Unit 1 Density Lab (Practice IA) Research Question: How does the size of a sample affect its density? Introduction: The density of an object is determined by dividing the object’s mass by its volume. Since density is essentially a ratio of mass:volume, as the size of the sample changes, the density remains the same. Therefore, density is an intensive property, or one that is independent of its size. For example, the density of pure water is 1.0 g cm regardless if we have a puddle of pure water or a bathtub full of pure water. In this lab, you will be comparing different sized blocks of wood using density to determine which blocks are made of the same material. Materials: OHAUS electronic balance, metric rulers, blocks of wood. Procedure: 1. Write down all of your qualitative observations about the blocks (physical characteristics). 2. Determine the absolute uncertainties of each instrument and then place those in the heading of each table. 3. The measurements of mass, length, width, and height have all been filled in for you. HOWEVER, you must correct the measurements to match the absolute uncertainty in the heading of your data table where necessary. 4. Calculate the volume of each block of wood and place the values in Data Table 2 (correct sig figs please). 5. Under sample calculations, show all work for your calculation of volume AND density for Block 1. Please be neat, include units and appropriate sig figs. 6. Under propagation of uncertainties, your instructor will guide you how to show all work for Block 1. 7. Repeat these steps for the remaining blocks and fill in your final propagated values for volume and density (with absolute uncertainties) for each block in Data Table 3. Pre-Lab: (Read the procedure above first) 1. The independent variable is the one that you (the scientist) is changing throughout the experiment. What is the independent variable in this experiment? size of sample 2. The dependent variable is the one that you are measuring in response to the independent variable. What is the dependent variable in this experiment? density in g cm* 3. Controlled variables are all other variables (aside from the independent and dependent variables) that must remain the same throughout the experiment. Changing these variables could negatively affect your data. Identify one variable that must be controlled in this experiment, explain how you will control it, and why it must be controlled. Controlled Variable How Will it Be Controlled Why Must it Be Controlled a. Keep same ruler between trials a. Ensure same ruler is a. To maintain consistent b. Keep temperature constant used for each block. absolute uncertainties for c. Keep same balance between b. Measure the measured values. trials temperature of the b. Temperature can affect room witha volume which, in turn, can affect density. MG 9/20 
