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CH141Lab1-1 - Scientific Measurements and Introduction to...

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Scientific Measurements and Introduction to Excel Pre-lab Assignment: Reading: 1. Chapter sections 1.4 and 1.5 in Brown, LeMay, Bursten & Murphy. 2. This lab handout! Questions: 1. What would be the density of an object with a mass of 1.65 g and a volume of 0.18 mL? 2. Three trials of a given experiment give you values of 14.7 s, 14.6 s, and 14.6 s. If the literature offers an accepted value for this experiment as 15.9 s, were your data accurate? Precise? Explain. Introduction In this experiment you will explore scientific measurements, including measuring mass with a balance, the determination of volume by water displacement, and errors in measurements. You will also use Excel–a spreadsheet program that you will find extremely useful throughout your Colby career. Make sure you learn the Excel skills covered by this experiment as they will be encountered in future labs when you are working alone. Whenever you make a spreadsheet or graph in Excel be sure to save each on the fileserver, and print both to attach to your discussion. Whenever you make a spreadsheet and use formulas, show example formula/calculations in your lab notebook. Percent Composition of Zinc and Copper in US Pennies The current US penny is made of metallic copper plated onto a zinc core. You are going to determine the density of pure copper and zinc metals as well as the density of pennies. From this data you will estimate the percentages of copper (Cu) and zinc (Zn) in pennies. In an object composed of multiple materials (like a penny), the density is a weighted average of the densities of the pure substances that make up the object. If the density of pure copper is d Cu and the density of pure zinc is d Zn , then the density (d) of a composite of copper and zinc is (p = the % Cu by mass and q = % Zn by mass): d = p d Cu + q d Zn 100 (1)
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2 Since pennies contain only copper and zinc: p + q = 100% and therefore q = 100-p: d = p d Cu + (100-p) d Zn 100 (2) If we know the % copper (p), we can solve for d. On the other hand, if we know the density of the composite (d), we can use equation 2 to obtain the % copper (p) in the sample. Procedure 1. Density of Cu, Zn, and Pennies : Working with your assigned partner, select three different types 1 of copper, three different types of zinc, and three different samples of pennies. Choose a different number of pennies for each of the three samples, keeping the samples distinct. Each partner will measure the mass of her/his samples on a balance (always protect the pan of the balance with a tared piece of weighing paper, weigh boat, or a beaker). Always record the balance number you are working on when you record mass data into your notebook. To determine the volume of your metal pieces and penny samples:
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CH141Lab1-1 - Scientific Measurements and Introduction to...

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