Expt 043 -- Mystery solutions -- 3

Description

The students are paired off, and each group is given two identical sets of solutions, one labeled 1, 2, 3 and the other, A, B, C. The students try to identify the matching solutions. What makes the lab especially challenging and what prevents one student from doing all the work and what forces them each to write down their observations is that they must seat themselves across the room from their partners, keep back to back. Students communicate with messages "faxed" back and forth to their partners.

Objectives

You and a partner in separate parts of the room are each given a set of chemicals. You must match the identical solutions by comparing your written observations.

Safety

Wear safety goggles. Avoid ingesting the chemicals. Wipe up spills with a paper towel. Wash hands after the experiment.

Procedure

The instructor may give you a kit of materials or ask you to prepare one.

Prepare a kit of chemicals.

One student uses solutions 1,2,3. The partner uses solutions A, B, C.

  1. Use pliers to twist out any prongs that might be in your cassette box.
  2. Cut off and discard the stems of three Super Jumbo plastic pipets. Cut the bulbs in half and push them down into the cassette box to act as holding cups.
  3. Label the "shoulder"(front and back) of three thin stem pipets with 1, 2, 3 (or A, B, C, whichever you were assigned) . Cut the stems down to 1 cm.
  4. Half-fill the three pipets with the three solutions, one in each.

Place the pipets in three of the holding cups in the cassette box . Use a permanent pen to make a large visible mark on the corner of an acetate sheet and place it in the box too.

Identify the identical chemicals

  1. Either fill your own plastic pipets as described above or obtain from the instructor a set of two tape boxes, one containing three numbered solutions, the other containing three lettered solutions. You take one box, and your lab partners takes the other, and move to opposite sides of the room, facing away from one another. Place one drop of one of the solutions on the plastic sheet (enclosed). Add a drop from a different solution to the first drop. (Note: to avoid contamination, make sure the second solution drops into the first: DO NOT STICK THE SECOND PIPET STEM INTO THE DROP OF THE FIRST SOLUTION.) Observe what occurs when the two drops mix. Repeat for all other combinations. Record your observations carefully.
  2. When you have recorded all of your observations, exchange information with your partner so that you can determine which of the lettered solutions (A, B, C) is identical to which of the numbered solutions (1, 2, 3). Communicate with your partner in writing only. Scientists often do this when collaborating with researchers working hundreds of miles away.
  3. Wipe up solutions with a paper towel, and dispose with ordinary trash. Return the chemical kits to the instructor.

Questions

Identify each solution as A, B, or C.

1 = ____

2 = ____

3 = ____