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In the Laboratory

www.JCE.DivCHED.org Vol. 81 No. 9 September 2004 Journal of Chemical Education 1337

The construction of two simple, inexpensive apparatusesthat clearly show the electrolysis of water are described. Bothapparatuses can be made by all students in any laboratory orclassroom. The apparatuses were developed for a course inoxidationreduction chemistry aimed at secondary school

instructors.Electrolysis of water is traditionally conducted in a

Hofmann apparatus, which is expensive and fragile. Sim-pler and less expensive apparatuses have been reported (13)as well as changes to improve the demonstration (47).Theapparatuses described here are appropriate for various gradesand curricula.

The two apparatuses are shown in Figures 1 and 2. Thechemistry involved is not included, as this can be found inany general chemistry book, as well as in the references citedabove. The components used to construct these apparatusesare disposable polyethene transfer pipets (also called Beral pi-pets) and floral wire (25 cm length, 1.1-mm diameter) from

a local florist. The volume of the pipet bulbs is 3.5 mL, butthe sizes of the stems vary. In these experiments 1-mL and3-mL stem pipets have been used, but this is not critical andsimilar ones will work equally well. Both the pipets and thewire are chemically stable for the use intended here. Remem-ber to use safety goggles during the experiment even thoughthe risk of injury is very low.

Apparatus for Electrolysis of Waterwith Hydrogen and Oxygen Collected Together

The complete apparatus is shown in Figure 1. It allowselectrolysis of water with collection of hydrogen and oxygentogether. It is made as follows:

1. Cut the stem of a pipet (1mL-stem type) so that about 0.5cm of the stem remains.

2. Push (while twisting) the floral wires through the top ofthe bulb and out again as shown in Figure 1B (the furtherdown the wires protrude from the bulb the more water willbe electrolyzed). Make the holes as small as possible as thepipet should remain water and gas tight. If the floral wirehas blunt ends, cut a diagonal at one end of the wire with a

wire cutter before pushing it through the pipet. The pipetshould not be sealed as water is forced out when the gasesare produced. The wires must not be in contact with eachother.

A Small-Scale and Low-Cost Apparatusfor the Electrolysis of Water

Per-Odd EggenSchool Laboratory for Science and Technology, Norwegian University of Science and Technology, 7491 Trondheim,Norway

Lise Kvittingen*

Department of Chemistry, Norwegian University of Science and Technology, 7491 Trondheim, Norway;*Lise.Kvittingen@chembio.ntnu.no

Cost-Effective Teacheredited by

Harold H. HarrisUniversity of MissouriSt. Louis

St. Louis, MO 63121

Figure 2. Apparatus for the electrolysis of water with separate col-lection of oxygen and hydrogen (bromothymol blue was added tothe solution). (A) Shows one-hand grip of the apparatus (two handsare more stable) before the electrolysis has started. (B) A close-upillustrating the gas volumes, changes of indicator color, and a standof floral wire (color changes from green in A to blue at the nega-tive electrode and yellow at the positive electrode; photo Roarhlander).

A B

Figure 1. Apparatus for the electrolysis of water with collection ofoxygen and hydrogen together (bromothymol blue was added to

the solution). (A) How to hold the apparatus: reaction starts whenthe wires are touched to the battery. (B) A close-up showing the gasdevelopment and changes of indicator color (solution color changesfrom green in A to blue and yellow in B; photo Roar hlander).

A B

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In the Laboratory

1338 Journal of Chemical Education Vol. 81 No. 9 September 2004 www.JCE.DivCHED.org

3. Bend the wires 90 degrees above the bulb (see Figure 1A).

4. Turn the pipet upside down and fill it with saturatedNa2SO4solution (it works well and is safe) and possibly anindicator (e.g., bromothymol blue) by using another pipet.Do not try to suck up the solution. Put a petri dish or an-other container under the open end of the pipet, into whichthe Na2SO4solution can run when the gases produced forcethe liquid out.

5. Connect the floral wires to a battery, preferably 9 V. Theelectrolysis starts immediately, the color changes (as a re-sult of the pH changes at the electrodes) and gas produc-tion can be observed. The electrolysis will continue untilthe water is at the level where the floral wires exit the pi-pet. Thus a drop of the solution remains in the bulb con-veniently sealing the gas inside.

6. Move the pipet near a flame and squeeze the bulb gently. Asurprisingly sharp pop will be heard. (You have probablynever made a more favorable ratio of hydrogen and oxy-gen!) This actually surprises the students considering thetiny quantity of gas mixture collected. This experiment is

an immediate winner and is promptly adopted for use inschools. In our experience even the least handy instructor

will succeed immediately. The apparatus described nextshould, for pedagogical reasons, be made first as no stu-dent is inclined to listen after the first pop is heard.

Apparatus for Electrolysis of Waterwith Separate Collection of Hydrogen and Oxygen

The complete apparatus for the electrolysis of water withreasonably controlled separate collection of hydrogen and oxy-gen is shown in Figure 2. The apparatus is made as follows:

1. Cut off the stem of two pipets (3-mL stem) so that about

0.5 cm of each stem remains.2. Push (while twisting) floral wires through the bulbs of the

pipets so that they protrude slightly from the stem (1/21cm) and bend the wires 90 degrees just above the bulb (Fig-ure 2A). Try to make the holes small so that the pipets re-main water and gas tight. If the floral wire is blunt, cut adiagonal at one end of the wire with a wire cutter beforepushing it through the pipet. The gases will be produced atthe protruding ends of the wires, therefore keep the wiresin the center of the stems, so that the gases bubble into thebulbs and not outside. This can be adjusted when the elec-trolysis is started. It is also possible to form a spiral in the

wire where it passes through the pipet stem, thus aligning

it better, but this is not necessary.3. Turn the pipets independently upside down and fill each

with saturated Na2SO4solution (it works well and is safe)and an indicator such as bromothymol blue. Adjusting thepH of the Na2SO4 solution until the bromothymol blueindicator turns green will help the students to understandthe half-reaction at each electrode, because the pH changescan be observed. If you want to have the apparatus in thestand when doing the electrolysis, put the pipets (with thefloral wires pushed in) into the stand before filling with satu-rated Na2SO4solution.

4. Turn the pipets, so that the open ends are immersed into asolution of similar composition and hold them next to eachother (Figure 2).

5. Connect the floral wires directly to a battery, preferably 9V (Figure 2A). In the classroom let the students work inpairs, one holding the two pipets in the solution, the otherkeeping the wires in contact with the battery poles. Theelectrolysis starts immediately and gas bubbles and colorchanges (if indicator has been added) can be observed.

6. Verify the gases produced, if desired.

The stand of floral wire (as shown in Figure 2B) is made bybending (i) one end of the floral wire around two pens (itemsof similar diameter) to allow for two pipets to be held and(ii) the other end around an appropriately sized cylinder, forexample, a vitamin jar. It is easier to make these two bendsin one plane before finally bending the stand into the shapeshown in Figure 2B. Alternatively hold the pipets in one handand the wires onto the battery with the other hand (Figure2A shows a one-handed grip). In the classroom let the stu-dents work in pairs as described above.

Discussion

The hydrogen ions and oxygen that develop during theelectrolysis at the positive electrode result in a slight reactionwith the iron in the wire. This is a minor problem for thegas production and can be ignored. However, some studentswill spot this, which advantageously allows a comment onconditions favoring the corrosion of iron. Information on thiscan be found in a standard general chemistry book (for ex-ample ref 8).To avoid corrosion a dilute solution of NaOHcan be used as a means of ion transport, but this demandssafety precautions and excludes the use of an acidbase indi-cator, which is very instructive. Even electrodes of copper,welding steel, and graphite from a normal school pencil areattacked at the positive electrode when a neutral salt (e.g.,Na2SO4) is used, thus we prefer the use of cheap floral wire.

Acknowledgment

POE is grateful for financial support from the Countyof Nord-Trndelag enabling him to work at the School Labo-ratory for Mathematics, Science, and Technology, NorwegianUniversity of Science and Technology.

Literature Cited

1. Suzuki, C.J. Chem. Educ.1995,72,912.2. Skinner, J.Microscale Chemistry, Experiments in Miniature;The

Royal Society of Chemistry: London, 1997; pp 1213.3. Ciardullo, C. V., C. M.Micro Action Chemistry,2 ed.; Flinn

Scientific: Batavia, IL, 1992; Vol.1, pp 6768.4. Heideman, S.J. Chem. Educ.1986,63,809.5. Skinner, J. F.J. Chem. Educ.1981,58, 10176. Zhou, R. E.J. Chem. Educ.1996,73,786.7. Kelsh, D. J.J. Chem. Educ. 1981,62,154.8. Zumdahl, S. S.; Zumdahl, S. A. Chemistry,5th ed.; Houghton

Mifflin: Boston, MA, 2000; pp 862866.

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