Experiment 1 - Anoka-Ramsey Community College



Lab Activity H2

Does It Make Cents?

OUTCOMES

After completing this lab activity, the student should be able to:

• properly use the balance provided in the kit, obtaining the maximum precision the instrument will allow.

• prepare a data table and graph which properly represents data collected in today’s lab activity.

• determine the number of pennies in an unknown sample from its mass.

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DISCUSSION

In this lab activity, the individual masses of several pennies dated 1983 or later will be measured. Then the mass of several different numbers of pennies will be measured. A graph will be prepared by plotting the mass of the pennies against the number of pennies. Finally, the mass of a sample containing a number of pennies that are unknown to you will be measured. By measuring their mass and using your graph, the number of pennies in your unknown sample may be determined.

There are a number of different types of graphs used to represent data and it would be nearly impossible to discuss all of them. The most common type of graph used in chemistry is the line graph, which has numbers on both the vertical and horizontal axes. In preparing this type of graph, the independent variable is placed on the horizontal axis (the x axis) and the dependent variable is placed on the vertical axis (the y axis). The independent variable is the variable you have experimental control over. The dependent variable is the variable that is affected by changes in the independent variable.

For example, if an experiment was carried out to determine how study time affects exam scores, the exam score would be the dependent variable, since the goal was to determine how the exam score depends on the amount of time spent studying for the exam. In this case, the vertical axis would be labeled with the exam score and the horizontal axis with time.

In this lab activity, the mass of a group of pennies will be measured and compared to the total number of pennies. Can you identify which variable is the dependent variable?

Once it has been determined which variable is the dependent variable, decide how the graph paper should be oriented. Always try to graph your data so it fills up as much of the page as possible. Before labeling your axes, determine how many units each division or line on your graph should represent. Also, determine the starting values for the vertical and horizontal axes. It is not necessary to begin every graph with zero. However, values should always increase as you move away from the origin and they should always increase in equal steps. Pick starting values and steps which are convenient and easy to work with. Number and mark off the major divisions along each axis. Label each axis with a description and the units, such as "study time (hours)".

Plot the data points onto the graph. The data points will be more visible if you draw a small circle around each dot. Then draw a line through the points that best represent the data. This is often called the best-fit line. The best-fit line does not always touch each point, due to errors in measurements. Also, the best-fit line is not always straight. In many graphs, the best-fit line is a curve. In virtually all cases, the best-fit line will be a smooth line. We do not play dot-to-dot.

Finally, every graph should have a title. The standard format is “y axis title vs. x axis title.” For example, “Exam Score vs. Study Time.” Now that we have discussed a few important aspects for this lab, are you ready to begin?

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|MATERIALS (Provided By Student) |MATERIALS (From Kit) |

|50 pennies (dated 1983 to today) |Electronic balance |

| |“Unknown” penny sample (do not open!) |

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PROCEDURE

1. Familiarize yourself with the use of the electronic balance in your kit. The mode button enables you to switch between different units of measurement. All measurements in this course will be made in grams (g). The tare button serves to zero the balance, with or without anything on the balance platform.

2. Tare the balance. Measure and record the individual masses of five different pennies from dated 1983 or later (post-1982). Calculate the average mass of the pennies.

3. Gather together 50 pennies from dated 1983 to today. Measure and record the combined mass of 0, 10, 20, 30, 40, and 50 pennies (mass the pennies together). REQUIRED PHOTO: Taken of this step – includes your face and/or clearly shows a Picture I.D. (with name), with all 50 pennies on the balance.

4. Place the vial containing an unknown (to you) number of pennies onto the balance. Do not open the vial.* Measure and record the mass of the vial containing the pennies, without counting the number of pennies in the sample. Also, record the sample letter (or number) on the vial. REQUIRED PHOTO: Taken of this step – includes the date clearly shown on a calendar, newspaper, cell phone, or written on a sheet of paper. Must also clearly see the vial number and mass on the balance display.

5. Subtract the mass of the vial from the total mass of the vial and pennies together to obtain the mass of just the pennies.

*Opening the vial constitutes cheating and may result in failing the assignment or course. The large majority of students will get the answer correct without the need to look. Kits returned with vials having broken seals will be questioned. It’s not worth the risk for a point or two.

Name Lab Section

PRELAB QUESTIONS

1. In a graph of exam score vs. study time (referred to in the discussion), which is the dependent variable and why?

2. Using the graph paper supplied, prepare a graph of the following data using the guidelines given in the discussion. Place the independent variable on the horizontal (x) axis and the dependent variable on the vertical (y) axis. Plot the points onto the graph, and draw the best fit line (or curve).

(Alternatively, you may use Excel or LoggerPro≠ to tabulate and graph your data.)

≠There is a short tutorial video on using LoggerPro on the main page for Lab H2.

|Study Time |Exam Score |Study Time |Exam Score |

|(hours) |(points) |(hours) |(points) |

|0 |24 |8 |67 |

|2 |34 |10 |79 |

|4 |45 |12 |88 |

|6 |57 |14 |98 |

3. Using your graph, how much study time is needed to obtain 85 points on the exam? This may be done by locating 85 points on the best fit line (or curve) and tracing back to the other axis to find the time. Express your answer in hours. Draw dotted lines (or use the position of the cursor on LoggerPro) on your graph to show how you found your answer.

4. In the post-lab questions, you will be graphing mass of pennies vs. the number of pennies. Identify the dependent and independent variables.

5. Which safety precautions, if any, must be observed during this lab activity?

PHOTOS - Please compress photos and save your file before uploading to the dropbox. Photos should come close to filling the boxes below and all required items should be clearly visible.

|Required Photo 1: |

|Required Photo 2: |

Name Lab Section

DATA

|Table 1. Individual Masses of Post-1982 Pennies |

|Penny #1: | |Penny #4: | |

|Penny #2: | |Penny #5: | |

|Penny #3: | |Average: | |

|Table 2. Masses of Groups of Post-1982 Pennies |

|Number of pennies |Mass |

|0 | |

|10 | |

|20 | |

|30 | |

|40 | |

|50 | |

|Table 3. “Unknown” Sample of Post-1982 Pennies |

|Unknown sample vial number | |

|Mass of vial (including pennies inside the vial) | |

|Mass of empty vial (given on notecard in kit) Do not open the vial! | |

|Mass of pennies | |

Name Lab Section

POSTLAB QUESTIONS

1. If necessary, review the paragraphs on graphing in the Discussion section. Using the supplied graph paper, prepare a graph in which you plot the mass of different numbers of pennies vs. the number of pennies. Remember to make your graph fill the whole page and to place each variable on the correct axis. Draw the best-fit line (or curve). Make sure you title your graph and label the axes.

(Alternatively, you may use Excel or Logger Pro to tabulate and graph your data.)

2. What is the average mass of your post-1982 pennies (from Table 1)? Using this average, calculate the number of pennies in your unknown vial. Do not open the vial! Read the bottom of page H2.2.*

3. Using your graph, locate the mass of the pennies for your unknown sample and use it to estimate the number of pennies in your unknown. Draw dotted lines on your graph (or use the position of the cursor on LoggerPro) to show how you found your answer. How many pennies do you calculate using this method? Do not open the vial! How does this compare with the number of pennies you found in question 2?

4. Using your graph, estimate the mass of 24 pennies. Draw lines on your graph (using a different color or different dashes) to show how you found the mass. Express your answer below, using the correct units.

5. The masses of 5 individual M&Ms are given below. If a bag contains 2739.4 g of M&Ms, how many M&Ms are in the bag? Show your calculations and round your answer to the nearest M&M.

0.8565 g

0.8973 g

0.8367 g

0.7998 g

0.8740 g

Lab Report Submission Checklist

Complete the appropriate checklist and submit this page along with your lab activity.

Lab Activity Submitted Via the D2L Dropbox

| |Prelab assignment is complete. |

| |Remainder of lab activity is complete (data, questions, photos. etc.). |

| |Required photos of the procedure included. |

| |At least one photo shows face or photo I.D. At least one photo clearly shows the date. |

| |Document filename in format of Lastname Firstname HX. |

| |File size is no larger than 10 MB. |

| |Only one document submitted for this lab activity. |

| |Lab submitted on time. |

| | |If late, this is your first extension. |

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Lab Activity Submitted Via the US Postal Service or In Person

| |Prelab assignment is complete. |

| |Remainder of lab activity is complete (data, questions, photos. etc.). |

| |Required photos (at least one showing face or photo I.D.; at least one shows the date) of the procedure or a tangible artifact or |

| |product from the lab activity is included. |

| |If return is desired, a self-addressed stamped envelope with sufficient postage is included*. |

| |Lab submitted on time (postmarked by due date if sent via USPS). |

| | |If late, this is your first extension. |

*You may find a postage calculator at . Use the balance in your kit to find the weight.

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