Appendix

MICROSCALE CHEMISTRY EXPERIMENTATION FOR HIGH SCHOOLS
PART II: HOME-MADE EQUIPMENT

Reprinted, with permission, from CHEM 13 NEWS, #200 (January 1991), pages 4-7.

Geoff Rayner-Canham, Deborah Wheeler and William Layden
Chemistry Department
Sir Wilfred Grenfell College
Corner Brook NF A2H 6P9

(Part 1 in this two part series appeared in our December issue, pages 8-10. We welcome good microscale experiments and suggestions for home-made microscale equipment - see page 6 [page 165 of this Guide], for example - from our readers.)

In Part 1 of this series, we looked at microscale equipment that was commercially available. Almost all of the items were polymer-based rather than glass. For those of us whose memories of glassblowing were of frustration and despair, the arrival of plastic ware enables us to create new items of equipment with nothing more than a sharp knife, an electric drill, and a sturdy glue. To illustrate, we will describe here three useful items that can be constructed easily.

A Gas Collection Apparatus

The concept of this apparatus originated (we believe) with Robert Becker of Greenwich High School, CT. However, we have taken the original glass design and made a simpler and more robust apparatus from polyallomer. The basic requirements are a 1.5 mL microtube (1) and a graduated 1 mL micropipet (2). Drive a 7/64" hole through the centre of the cap of the microtube. Cut the micropipet as shown below and save sections (a), (b) and (c). Insert section (a) through the bottom of the microtube cap until the wider part of the stem rests against the underside of the cap.

Fig. 1

To prepare hydrogen, fill the bulb (c) about three-fourths full with water (3). Place some zinc granules and hydrochloric acid in the microtube, cap the microtube and lower the open end of the bulb over the stem as in Fig. 2. Squirting the collected gas at a flame gives a loud sound.

Fig. 2

For carbon dioxide, use a completely water-filled bulb. Place marble chips and hydrochloric acid in the microtube, cap the microtube and collect the carbon dioxide in the bulb. To test the gas, half-fill a microtube with lime water (CHEM 13 NEWS, March 1990, page 4). Insert the stem section (b) 'backwards' into the bulb section (c) as an extension and place the end beneath the level of the lime water. Squeezing the bulb should result in a cloudiness in the lime water.

A Simple Electrochemical Cell

A simple electrochemical cell can be constructed by drilling a hole in the side of two 1.5 mL microtubes and linking the two by means of a length of plastic tube (4). We use a length of about 1.6 cm so that the resulting cell will fit into a microtube rack (5). To seal the joints, we use the general purpose glue 'Goop' (6). The call can be used to measure potentials between different metals by filling the apparatus with sodium sulfate solution and inserting narrow strips of dissimilar metals. To connect the strips to a voltmeter, we use the mini-alligator clips (7) joined to the wires with low-temperature solder (8). To minimise the possibility of an air bubble trapped in the cross-arm, we add a small quantity of detergent to the solution.

An Electrochemical Cell with Divider

The same type of cell can be created with a partition to enable standard cell potentials to be determined (Fig. 3). For the divider, we use the microtube filter inserts (9). The rim is cut off to leave a length of about 1.6 cm. Holes are drilled in the sides of two microtubes and the fitter insert sealed in place with "Goop'. A copper(II) sulfate solution can be placed in one arm and a zinc sulfate solution in the other.

Fig. 3

Again we recommend the addition of a small quantity of detergent to the solutions to improve the 'wetting' of the filter insert. Insertion of thin strips of copper and zinc metal allows the measurement of the standard cell potential.

Comments

The possibilities of construction of microscale equipment are limited only by your imagination. We encourage others to devise specific items of plastic ware that can enable a wider range of microscale experiments to be performed. Details of the experiments will be available in a forthcoming laboratory manual.

References

1. Catalog No. 505-101, PGC Scientifics Corp., P.O. Box 7277, Gaithersburg, MD 20898-7277, USA. Telephone (800) 323-5130.

2. Large bulb, 1 mL graduated micropipet from MicroMole Scientific, 1312 N15th, Pasco, WA 99301, USA. Telephone (509) 545-4904.

3. We find that if the bulb is only partially filled with water, the hydrogen collected gives a very noticeable 'pop', but a filled bulb gives a very quiet ignition.

4. We use lengths of polyethylene tube cut from 400 mL microcentrifuge tubes. Catalog No. F19928, Bel-Art ScienceWare, avaliable from most suppliers such as Fischer, Canlab/Baxter, etc.

5. Catalog No. 277-010, PGC Scientifics; Catalog No. 2509-36, Canadawide Scientific, 1230 Old Innes Road, Unit 414, Ottawa, ON K1B 3V3. Telephone (800) 267-3787.

6. Obtainable from hardware stores. We find that other types of glue do not adhere well to the plastic surface. The "Goop" gives a solid but flexible joint, though tell students not to put stress on the cell as the glue has limited strength. If anyone discovers an alternative glue or cement please let us know.

7. Catalog No. 270-373, Radio Shack.

8. This solder can be melted with a match. Catalog No. 64-010, Radio Shack.

9. Catalog No. 352-109, PGC Scientifics.

Student Data Table

1. mass of steel wool (iron) _______grams
2. mass of filter paper _______grams
3. mass of dry filter paper and brown copper residue _______grams
4. mass of copper _______grams

Calculations

1. moles of iron used moles _______moles
2. moles of copper produced _______moles
3. mole ratio of iron:copper _______
4. lowest whole number mole ratio of iron : copper _______

Discussion

Groups of students can compile their results, doing statistics, e.g., average deviation and standard deviation. Quantitatively, results are comparable to those obtained in experiments using large quantities of reactants. Student errors in calculation and the occurrence of unreacted steel wool have accounted for most errors.

Students may have difficulty perceiving of the brown residue as copper, not rust. After the lab, h is helpful if the teacher uses some of the copper residue and some of the steel wool in separate reactions with 6 M nitric acid. Do it in the hood. Use some authentic iron oxide and copper too if you have them at hand. The contrast in the colors of the solutions from each reaction will help students identify the residue from the experiment as copper.

The use of the micro funnel could be adapted to many other experiments involving collection of the residue from filtration. The porosity of the required filter paper would depend on the nature of the precipitate being collected.

Hazards

In the student experiment copper(lI) sulfate is a skin irritant. Use the hood for the teacher demonstration because reactions of copper or iron with nitric acid produce the hazardous gas, nitrogen dioxide. Nitric acid is corrosive and strongly oxidizing.

Reference

Harold W. Ferguson et al., 1970, Investigation 15 "Mole Ratios and Chemical Reactions: 11', in Laboratory Investigations in Chemistry, Morristown, New Jersey, Silver Burdett, pages 92-97.