Measuring Mass Pre-Lab Discussion The ability to measure accurately the mass of an object is an important skill in the chemistry laboratory. You can use a triple beam balance to measure mass. A balance has several parts: 1) the pan: flat surface on which you place the object to be measured; 2) three beams :indicate the mass of the object. Notice that each beam has a different scale. Each beam carries a weight called a rider. You find the mass of an object by placing it on the pan and moving the riders until the pointer on the right of the balance stays pointed at zero. Purpose: a) To become proficient in measuring the mass using a triple beam balance b) to analyze the composition of a penny Procedure: Find the individual mass of your five pennies to the nearest 0.01 g. Share data with two other lab groups Data: Mass of penny 1: _________ g Date: _______ Mass of penny 2: _________ g Date: _______ Mass of penny 3: _________ g Date: _______ Mass of penny 4: _________ g Date: _______ Mass of penny 5: _________ g Date: _______ Mass of penny 6: 3.20 g Date: 1975__ Mass of penny 7: __3.15____ g Date: _1979___ Mass of penny 8: __3.09____ g Date: _1980___ Mass of penny 9: __2.49___ g Date: _1991__ Mass of penny 10: __2.58____ g Date: _1983___ Mass of penny 11: __2.45____ g Date: _1985___ Mass of penny 12: __3.19____ g Date: _1981___ Mass of penny 13: __3.13____ g Date: _1982___ Mass of penny 14: __2.47____ g Date: _1984___ Mass of penny 15: __2.57____ g Date: _1989___ Mass of penny 16: __2.51____ g Date: _1987___ Mass of penny 17: __3.13____ g Date: _1978__ Mass of penny 18: __2.57____ g Date: _1990___ Analysis: (SHOW ALL WORK) 1. Organize the data into a chart. ( date vs mass of penny, in chronological order) 2. Make a graph of the data with date on the x-axis and mass on the y-axis 3. Predict the year that the penny’s composition changed 4. Find the average mass of an old penny 5. Find the average mass of a new penny 6. Because of the rapid rise in the price of copper, the Bureau of Mint changed the composition of the penny. The new penny is now an alloy of 97.6% zinc and 2.4% copper. Prior to the change, pennies were made up of 95.0% copper and 5.0% zinc. It’s virtually impossible to tell the difference between the pennies just by looking at them. However, since Cu is more dense than Zn, and because the volumes of the pennies are the same, the old pennies will have a greater mass than the new ones. a) Based on the percent composition of the old and new pennies, calculate the grams of Cu and the grams of Zn in the old penny and the new penny. b) If I can buy 500 g of Cu for $39.92 and 500 g of Zn for $18.50, what would an old penny cost and what would a new penny cost?
Posted on: Thu, 21 Aug 2014 00:22:14 +0000