Heather Haley
Product Developer

September 2015

Background

As discussed in our previous Carolina Tips® article “Paper Clip Chemistry,” paper clips are a great tool to explore a variety of chemistry concepts, including measurement, matter, atomic structure, chemical reactions, and gases.

If a wide variety of paper clips are available, you can use them to help students understand empirical formulas and relative masses. Suggested paper clips include:

Materials

• Mini Paper Clips (no. 3, box of 100)
• Small Paper Clips (no. 1, box of 100, item #971720)
• Large Paper Clips (jumbo, box of 100, item #971708)
• Owl Clips (also called regal clips, no. 3, box of 100)
• Butterfly Clips (also called ideal clamps, no. 1, 2 boxes of 50)
• Balances

Preparation

1. Without counting, prepare samples of 2 clip types for each group. Suggested clip combinations include:
   1. Lg and Sm
   2. Lg and Mi
   3. Lg and Ow
   4. Bu and Lg
   5. Ow and Sm
   6. Bu and Sm
   7. Sm and Mi
   8. Bu and Mi
   9. Ow and Mi
   10. Bu and Ow
2. Assign each group of students a set of 3 chemical equations to study. Each equation uses 2 types of paper clips abbreviated using a 2-letter symbol (analogous to a chemical element). Each equation set has the form:
   1. 
      Equation 1: Lg + Sm → LgSm
      
      Equation 2: 2Lg + 2Sm → Lg₂Sm₂
      
      Equation 3: 3Lg + 3Sm → Lg₃Sm₃
3. Provide each group with a set of blank data tables to record their results and provide a framework for relevant calculations. Sample data tables follow each part of the procedure below.
4. Determine your desired procedure for sharing class data with all students.

Procedure

Part 1: Paper clip data

Equation 1

1. Use a balance to find the mass of each type of clip and record it.
2. Connect 1 of each type of clip according to Equation 1. Continue connecting clips until 1 type of clip is used up.
3. Find the mass of combined clip products and record it.
4. Find the mass of any remaining clips in excess and record it.
   Note: The total mass of clips before combining is the same as the total mass of combined paper clips and remaining paper clips, illustrating the law of conservation of mass.
   
5. Unhook all combined clips.

Equation 2

6. Use a balance to find the mass of each type of clip and record it.
7. Connect 2 of each type of clip according to Equation 2. Continue connecting clips until 1 type of clip is used up.
8. Find the mass of combined clips and record it.
9. Find the mass of any remaining clips and record it.
10. Unhook all combined clips.

Equation 3

11. Use a balance to find the mass of each type of clip and record it.
12. Connect 3 of each type of clip according to Equation 3. Continue connecting clips until 1 type of clip is used up.
13. Find the mass of combined clips and record it.
14. Find the mass of any remaining clips and record it.
15. Unhook all combined clips.

Part 2: Conservation of mass and mass percent calculations

1. Use the data in Table 1 to calculate the total mass of reactants and the total mass of products and excess reactants.
2. Do the values you obtained support the law of conservation of mass?
3. Use the data in Table 1 to calculate the mass of the first reactant used and the second reactant used.
4. Copy the mass of product from Table 1.
5. Do the values you obtained support the law of conservation of mass?
6. Calculate the mass percent of each reactant using values in Table 2.
7. What do you notice about the mass percent for each product in Table 2? What does this imply about the empirical formulas of each product?

Part 3: Class paper clip mass percent and mass ratios

1. Locate the data you recorded for Equation 1 in Table 2.
2. Locate the formula for your group’s Equation 1 product. Record this on the first row in Table 3.
3. Copy the data for mass of first reactant used, mass of second reactant used, and mass of product from Table 2 to Table 3.
4. Repeat steps 1–3 for data recorded for Equation 1 by other groups.
5. Calculate the mass percent of each reactant using values in Table 3.
6. Calculate the mass ratio for each reactant using values in Table 3.

Part 4: Class paper clip relative masses

1. Identify the reactant with the smallest mass percent in Table 3.
2. Set the mass of this reactant equal to 1.000 clip mass units (cmu).
3. Use mass percent data from Table 3 to set up proportions and calculate the relative masses of each clip as follows:

Extension activity

1. Assign each type of clip to represent an element (e.g., carbon = Ow, hydrogen = Sm, oxygen = Lg), and write the key in a location visible to students.
2. Write down the chemical formulas for simple chemical compounds in a location visible to students. For example:
   1. CH₂O, formaldehyde
   2. CH₃OH, methanol
   3. C₂H₅OH, ethanol
   4. C₆H₁₂O₆, glucose
   5. C₃H₇OH, isopropanol
   6. H₂CO₃, carbonic acid
   7. C₂H₄O₂, acetic acid
   8. (CH₃)₂CO, acetone
   9. HCOOH, formic acid
   10. C₄H₁₀O, ethyl ether
3. Ask groups to build 2–5 molecules of the compound of their choice, then disassemble the clips and place them in a plastic bag.
4. Trade plastic bags between groups.
5. Have each group determine the empirical formula of the compound in the bag using the relative mass of each clip from Table 4.
6. If possible, have each group attempt to identify the chemical compound the first group used to place clips in the plastic bag.

Related items

• Inquiries in Science®: Reconstructing Atomic Theory Kit (item #251219)
• Inquiries in Science®: Determining Chemical Formulas Kit (item #251206)
• Carolina Investigations® for AP® Chemistry: Gravimetric Analysis of a Carbonate Kit (item #840570)

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