chemistry lab 1b - Number of pre-1982 pennies Average mass...

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Student Name: Huang Shan Lab Section Number: 6003 Student Number: 998549600 TA Name: Melissa Massey Experiment 1B COUNTING BY WEIGHING Date Performed: September 20, 2010 Date Submitted: October 05, 2010
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Introduction: Chemists determine how many individual atoms or molecules are in a bulk sample of matter from mass of the sample .In this experiment the process of “counting by weighting” will be demonstrated using U.S. pennies as the item to be counted. The pennies will represent individual atoms of a particular element. Procedure : 1. Se perate the 25 pennies into two piles: those that have date up to and including 1981, and those that have data from 1983 to the present. 2. Weigh each of the pre-1982 pennies and record the masses on the data sheet. Calculate the average mass of the pre-1982 pennies. 3. Weight each of the post-1982 pennies, record their masses on the data sheet and calculate the average mass.
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Result and conclusion
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Unformatted text preview: : Number of pre-1982 pennies Average mass of pre-1982 pennies Number of post-1982 pennies Average mass of post-1982 pennies Average mass of a U.S. penny Percentage of pre-1982 pennies in sample Percentage of post-1982 pennies in sample 167 3.0886 358 2.5001 2.6873 31.81% 68.19% Answers to the Question: 1. In a 1000g sample of the pennies used in the experiment, how many would you expect to be pre-1982 and how many post-1982? Solution: 392.99 will be pre-1982, 607.01 will be post-1982. 2. Calculat e the weighted average mass of the pennies that you weighted. How does it compare to 3.e.above? Explain . Solution: The average mass of my pennies is 2.7924 which is heavier than the data above. Because the percentage of pre-1982 pennies in my experiment is 36% which is larger than 31.81%. What is more, the pre-1982 pennies is heavier than post-1982 pennies....
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chemistry lab 1b - Number of pre-1982 pennies Average mass...

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