Density Of A Penny 4to2d

Name: Simone Yhap

SC_____-_____ Date: October 3, 2012 EXPERIMENT 2B: DENSITY OF A PENNY

Equipment: triple beam balance, graduated cylinder, meter sticks/tape measures Materials: 10 pennies In this lab you will examine a few different methods for calculating the density of a penny. Part I. Density using the Meter Stick and Balance In your lab work you will use a triple beam balance, which is a sensitive instrument used to measure mass that must be handled with care; your teacher will demonstrate the proper technique. You will use a meter stick or tape measure to measure the height and diameter of the penny. Be sure to include units and the correct number of significant figures in the table below. Penny Height 1 0.1 cm (0.01 m) 2 0.2 cm (0.02 m)

Diameter 1.9 cm (0.019 m) 1.8 cm (0.018 m)

Mass 3.3 g (0.0033 kg) 2.9 g (0.0029 kg)

(12 pts)

Calculations: A. Find the volume of each penny using the equation V=h*π*(0.5000*d)2 Be sure to report the volume to the correct number of significant digits and with correct units. (8 pts) Penny 1 V=h*π*(0.5000*d)2 V= (0.1 cm) *π*(.5000*1.9 cm) 2 V= 0.3 cm3

Penny 2 V=h*π*(0.5000*d)2 V=(.2 cm)*π*(0.5000*1.8 cm)2 V= 0.5 cm3 V= 0.5 cm3

V=0.3 cm3

B. Find the density of each penny by dividing the mass by the volume, be sure to use the correct number of significant digits and with correct units. (8 pts) Penny 1 Density=

Penny 2 Density=

D=

D=

D = 11 g/ cm3 D = 11 g/ cm3

D= 5.8 g/ cm3 D= 5.8 g/ cm

3

1. Why are the densities of the two pennies different? (4 pts) The densities of the two pennies are different because each penny has a different mass and volume so that affects the density of every penny.

Repeat this experiment using ten pennies. You will measure the height of a stack of ten pennies and then measure the length of ten pennies. Mass all ten pennies at the same time. Be sure to include units and the correct number of significant figures in the table below. Height 0.15 cm (0.015 m)

Diameter 1.92 cm (0.0192 m)

Mass 2.64 g (0.00264 kg) (12 pts)

Calculations: (8 pts) Volume

Density

V=h*π*(0.5000*d)2

Density=

V= (0.15 cm) *π*(0.5000*1.92 cm)2 V=0.4

Density= Density= 6.6 g/

V=0.4

D= 6.6 g/

1. Compare measuring the volume of the single pennies to measuring the volume of ten pennies. Which method introduces more error? Why? (4 pts) The method that includes more error is measuring the volume of ten pennies because the mass, the diameter, and the height is harder to calculate. Part II. Density using the Graduated Cylinder Liquids are most easily measure by volume often using a graduated cylinder. Your teacher will demonstrate how to use this instrument and how to read a meniscus. A. Fill your graduated cylinder with water someplace between 10 and 20mL and record the value here with the correct number of significant digits: 15 mL (4 pts) B. Devise a procedure for calculating the density of a penny using the triple beam balance and the graduated cylinder. Check your procedure with your teacher before proceeding.

Write a step-by-step procedure below: (10 pts) 1. Make sure your pennies are completely dry. If they are not completely dry, then fully dry the pennies off with a paper towel. 2. Measure the mass of the 10 pennies on the Triple Beam Balance, and then divide your mass by ten. 3. Fill the graduated cylinder with 15 mL of water. To make sure that the graduated cylinder is filled to 15 mL, place the graduated cylinder on the table, and at eye level, look at the meniscus and if the meniscus is at the 15 mL mark, and then record your volume. If the volume is lower that 15 mL, add more water until the volume of the graduated cylinder is equal to 15 mL, and record your volume. If the volume is greater than 15 mL, pour out some of the water until it is at 15 mL, and record your volume. 4. Place the 10 pennies in the graduated cylinder, and record the volume (the 15 mL of water plus the 10 pennies).

5. Subtract the first volume (15 mL) from your second volume (15 mL plus the 10 pennies). This volume is the volume of the 10 pennies. Divide the volume by 10 to get the volume of one penny. 6. Divide the mass of one penny by the volume of one penny to get the density of one penny. Prepare one or more data tables and record your data below: (5 pts) Original Volume (before the addition of the 10 pennies) 15 mL

Pennies 10 Pennies 1 Penny

Mass 27 g (0.027 kg) 2.7 g (0.0027 kg)

21 6

Volume (0.021 L) (0.006 L)

Density 1.3 g/mL 0.45 g/mL

Show the work for the calculation of density: (5 pts) Density= D= D = 1.3 g/ml Density= D= D=0.45 g/mL Summary Questions (4 pts each) 1. For each instrument you used, how did you know to what precision to report the measurement? I knew what precision to report the measurements by looking at the number of significant figures in the given numbers, and which ever number had the lowest amount of significant figures, that is where I rounded my measurement up to. 2. What is the meniscus and how should it be read? The meniscus is the curve of the water line. The meniscus should be read by looking at where that curve is, and where ever that curve is, that is the volume of the liquid in the graduated cylinder.

3. What experimental error occurs with the method of calculating density you used in Part I? What error occurs with the method you devised in Part II? Which do you think is the better method? The experimental errors that occurred were, the white tick mark wasn’t exactly on zero, the pennies weren’t fully dry, and I could have measured the diameter or height incorrectly. The errors that occurred in part two were, not reading the meniscus properly, and filling the graduated cylinder with too little or too much water. I

think using the Graduated cylinder is the better method because it gives you more precise measurements, and there is less room for experimental error. 4. Why should you mass the pennies before placing them in the graduated cylinder? If you used wet pennies, would the density calculated be too high or too low? Explain. You should find the mass of the pennies before placing them in the graduated cylinder because if you place the pennies in the water first, then place the pennies on the triple beam balance, the pennies will have left over water on its surface, and that would increased the mass of the pennies, which would make us get a false measurement. The density would be too high because the equation for density is, , the larger the mass, the larger the density, but the smaller the mass, the lower the density.

5. Assume the density you calculated in Part II is the actual density (accepted value). Calculate the percent error for the density calculated for Penny 1 in Part I. See Table T for the formula. Show work and correct sig figs. Percent error = Percent error =

x 100 x 100

Percent error= 23. % Percent errors = 23. %

Conclusion: I believe that the using the graduated cylinder is the best way to solve for the density and volume of a penny because from the data the we collected, and looking at the percent error, we can see that when we use a meter stick/tape measure, our percent error is greater than ten percent, and by this being greater than ten percent it falls in between the rule of thumb, but since 23% is close to 30% we assume that this percent error is quite large, and by using a graduated cylinder, our data is more precise/accurate.