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Experiment Two: Measurement in the Laboratory Determination of Density |
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In this lab you will Learn how the Bunsen burner works most efficiently Calibrate and use thermocouples Use significant figures in measurements and calculations
Print off a copy of the grading sheet for this lab.
How to Use the Top-loading Electronic Balanc Estimating Between Graduations Proper construction of a line graph Significant Figures and the Factor-Unit Method
Introduction: In this experiment you will learn how to use the laboratory equipment that will be used throughout the semester. You will learn how to use a top-loading balance and how to correctly read the graduated cylinder. In addition, you will learn how to use the Bunsen burner most efficiently. You will learn the function of the various parts of the Bunsen burner and how properly adjust the flame. You will also learn how to correctly calibrate and use the thermocouples for taking the temperature in the laboratory. Thermocouples will be used in place of thermometers for measuring temperature in the lab. Work in the laboratory often involves measurements and calculations using data obtained by measurement. In doing these calculations, you must be aware of the correct number of significant figures that may be reported and the use of conversion factors used in converting data from one unit to another. This lab session will introduce you to the importance of significant figures. Density is a physical property that can be determined by making mass and volume measurements. We will determine the density of several liquids and an irregularly shaped solid. The relationship between mass and volume will be demonstrated via the construction of a graph. Calculations involving significant figures: It is important to be able to express answers from calculations to the correct numbers of significant figures in order for the result to be meaningful. If calculations are done using a calculator, the answer frequently has more significant figures than are justified. Therefore, it is important for you to be able to determine how many significant figures are allowable and how to round the answer to give you the proper number of significant figures. Additionally, it may be necessary at time to convert a quantity from one unit to another. The simplest way to perform these calculations is to use the "unit-factor" or "factor-label" method. In the unit-factor method a quantity in one unit is multiplied by a conversion factor. It is important when using the factor-label method that the equation is set up to that the unwanted unit(s) cancel. For example:
Density and Specific Gravity: Density is a physical property of a matter which may be useful in the identification of substances. The density of substance is equal to the mass divided by the volume. Another physical property is the specific gravity. The specific gravity is the density of a substance divided by the density of water at the same temperature. Because the density of water is very close to 1, the specific gravity of a substance is equal to its density. However, it is important to note that density measurements have units of m/v, while the specific gravity is a unit-less number.
Read the introductory material on the webpage. Read Experiment Two in the laboratory manual. Answer the Pre-lab questions on page 21 of the lab manual. You are encouraged to do the Application Questions at the end of Experiment Two before coming to lab. Answer the following questions from your McMurray textbook:
Solid wastes may be disposed of in the wastebasket. Place any unused “liquid” in the specially labeled waste container located under the hood.
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