Media

Abstract

Text book and black board are the classical media used in every class and every type of school. The term media can be discussed under the aspects of media education as well as under the aspects of media didactics (see Fig. 4.1). This text will address the basic questions of media didactics: “It deals with the functions and effects of media in teaching and learning processes. Its goal is the advancement of learning processes through a didactically appropriate organization and methodically effective use of media. The choice of media and their use should be appropriate for the teaching goals, contents and methods” [2].

Appendices

Problems and Exercises

• P4.1. Media can have different functions in chemistry lessons. Choose three functions and, by using issues of your choice, explain the use of certain kinds of media according to the chosen function.

• P4.2. One kind of media that is equally important for teachers as well as students is the text book. Choose three current text books and decide which book you would use for your lessons. Justify your choice and indicate your criteria.

• P4.3. Blackboard and overhead projector are the most important media in the class room. Write down advantages and disadvantages for their use. Explain two different teaching situations in which you use the one and the other medium. Give your reasons.

• P4.4. Due to its multiple possible uses, the computer is getting more and more important for school lessons. Explain three different teaching situations, in which you would use the computer in your chemistry lesson.

• P4.5. Mass media like television and newspapers have a big impact on the thinking and acting of your students. In which way can this impact be positive for your lessons, in which way can it be negative? Give examples.

Experiments

• E4.1. Illumination of apparatuses with the overhead projector

  Problem: It is sometimes hard for all of the students to observe a demonstrated experiment clearly. With the help of the mirror system of the overhead projector the bright light can be cast on the apparatus to improve the students’ observation.

  Material: Syringe, test tube with side tube and stopper, rubber hose; diluted hydrochloric acid (C), magnesium ribbon (F).

  Procedure: Syringe and test tube are to be attached to stands and connected, the test tube is to be half-filled with hydrochloric acid. A 5-cm piece of the magnesium ribbon is to be put into the test tube, which is to be closed with the stopper just afterwards. The light of the projector is to be cast on the apparatus.

  Observation: The gas generation, the disappearing metal and the increasing volume in the syringe can be easily observed due to the bright light on the apparatus.

• E4.2. The overhead projector surface as an experimental table

  Problem: The bright projection surface of the overhead projector itself can function as a good experimental table and can be used to run small experiments. The model experiment for the demonstration of the dynamic chemical equilibrium, for example, can be run on the projector surface. This way the experiment can be very well observed from all students.

  Material: Two 50 mL-measuring cylinders, two glass tubes of the same lengths (Ø: 8 mm and 6 mm); diluted copper sulfate solution (Xn)

  Procedure: One of the cylinders is to be filled with 50 mL of the blue solution, the other cylinder remains empty. Two glass tubes of the same diameter are used to lift and carry the solution from one cylinder to the other, until the volumes are equal in both cylinders. This experiment is to be repeated with glass tubes of different diameters. The volumes and the corresponding number of lifting processes can be illustrated in a chart.

  Observation: Equal volumes only result in the first case. In the second case the volume ratio is for example 35:15. The volumes remain on this level even with further lift processes.

• E4.3. Projection of electrolysis experiments

  Problem: When the illumination of an apparatus does not improve the observation for the student, it is possible to project phenomena with the overhead projector, as long as they take place in transparent solutions. Especially when new substances only originate in small amounts, like during electrolyses, the projection is a good way to magnify the reaction dish and to make the electrolysis observable for all students.

  Material: Petri dish, two pieces of platinum wire, transformer and cable; zinc bromide solution.

  Procedure: The two pieces of platinum wire (the electrodes) are to be attached to the Petri dish and with the cables connected to the transformer’s direct current poles. The Petri dish is to be put on the projector and the bottom is to be filled with zinc bromide solution. A direct current of about 5–10 V is to be set.

  Observation: One can directly observe the precipitation of yellow bromine on the positive pole and the creation of zinc crystals on the negative pole. With the right voltage it is possible to see the growth of a “zinc tree”. This is better visible with the help of the overhead projection.

• E4.4. Experiments in the projected Petri dish

  Problem: Many reactions take place in colored solutions; these colors can be made visible if light shines through the solution. Since there is an overhead projector in every chemistry class room, Petri dishes, especially the ones with three compartments, are interesting for showing colored solutions and their reactions. Different reactions can be observed at the same time.

  Material: Tripartite Petri dish, pipet; acid-base indicator (F), hydrochloric acid (C), sodium hydroxide solution (C)

  Procedure: The three compartments of the Petri dish are to be filled with an indicator solution, for example universal indicator dissolved in tap water: this solution is green. One drop of hydrochloric acid is to be added to the first compartment, one drop of sodium hydroxide solution to the second compartment. One drop of the acidic or basic solution can be used to neutralize the solutions in both compartments of the Petri dish.

  Observation: The green indicator solution shows a color change to red and blue. The projector makes it possible to see the streaking and the magnificent play of colors before the colors of the solutions finally change. The colors of the solutions in the first and second compartment can be compared to the color of the green indicator solution in the third compartment of the Petri dish. After neutralization just the green color is to be observed.

• E4.5. Special cuvette for the projection on the overhead projector

  Problem: Besides the possibility of projecting Petri dish experiments, there exists special equipment for the projection of reactions in test tubes or cuvettes. Due to a mirror system, new equipment projects the content of a test tube upright, older equipment cannot do that: solids precipitate in the projection from bottom to top.

  Material: Special equipment for the projection, test tubes; phenolphthalein solution (F), petrol (F/Xn/N), sodium (C/F).

  Procedure: The projector is to be switched on. The test tube is to be filled with diluted indicator solution. The indicator solution is to be covered by 2 cm of petrol. A small piece of sodium is to be pitched into the test tube.

  Observation: The piece of sodium immerses into the colorless indicator solution, the color of the indicator changes to red. A gas generation can be observed for a short time. The metal piece ascends in the phase of petrol, but drops back into the solution and reacts under the generation of gas. These processes recur until the sodium has dissipated.

• E4.6. Measuring cell for the projection on the overhead projector

  Problem: Small amounts of gas, especially ones that are to be measured quantitatively, can be better observed, if the apparatus is being projected in a large format. The quantitative water electrolysis is a good example for this kind of experiments.

  Material: Measuring cell, transformer, cable, sulfuric acid solution (C).

  Procedure: The measuring cell is to be filled with sulfuric acid solution on the projector, the transformer is to be switched on at 5 V, so that a constant gas formation sets in. Hydrogen and oxygen can be confirmed with common tests when the gas volumes are big enough.

  Observation: Gas bubbles form on the electrodes. The gas volume on the negative pole is twice as big as the gas volume on the positive pole. Hydrogen occurs at the negative pole, oxygen at the positive pole.

• E4.7. Experiments with the help of a gooseneck camera

  Problem: Not every reaction in a solution can be projected and observed with the overhead projector. Precipitates, for example, always appear to be black. One possibility to show these and other phenomena true to the original is to use a gooseneck camera with a connected monitor.

  Material: Gooseneck camera, monitor, test tubes; iron(II) chloride (Xn), iron(III) chloride (Xn), diluted sodium hydroxide solution (C).

  Procedure: One test tube is to be filled with diluted iron(II) chloride solution up to two thirds, the other test tube with the iron(III) chloride solution. These test tubes are to be attached to stands and then enlarged with the help of the camera and the monitor. A few drops of sodium hydroxide solution are to be added to both test tubes.

  Observation: The precipitation of green respectively brown iron chloride can be observed. The real colors of both precipitates can be compared on the monitor.

• E4.8. Large display of measured values on the computer screen

  Problem: Digital measuring instruments with big numbers or with large display are very expensive. The cheap solution for a large display of measured values is the computer screen. An AD-converter and the appropriate software make it possible to connect regular measuring instruments to the computer to display digital measured values.

  Material: Computer and AD-converter, software, balance, Petri dish; acetone (F).

  Procedure: The balance is to be connected to the computer with the help of the AD-converter. The large display of the measured values is to be prepared with the appropriate software. A few drops of acetone are to be put into the Petri dish, which is placed on the balance.

  Observation: The measured values are displayed in a large format on the screen. They show a decreasing mass of liquid acetone.

• E4.9. Recording and processing of measured values with the computer

  Problem: Some reactions are so fast that they cannot be recorded with traditional methods. A neutralization reaction of an acidic with an alkaline solution and recorded pH values can be realized with a connected computer: one can easily capture the pH jump around the equivalence point. It might be a good suggestion to let the students run some titrations and titration curves in the traditional way, to compare them to the computer’s way of recording.

  Material: Computer and software, connected AD-converter, calibrated pH-meter with glass electrode, magnetic stirrer, Erlenmeyer flask, burette; 0.1 molar solutions of hydrochloric acid and sodium hydroxide (C).

  Procedure: The pH-meter is to be connected to the computer via the AD-converter; the titration is to be prepared with the appropriate software. 50 mL of hydrochloric acid are to be poured into the Erlenmeyer flask, diluted with water, the magnetic stirrer is to be turned on, the electrode is to be immersed and the titration is to be started with the sodium hydroxide solution.

  Observation: Before the titration the pH-value is 1.0. During the titration the computer screen draws the titration curve. Adding 50 mL of sodium hydroxide solution the pH value jumps near a pH of 7; after adding a few more milliliters of sodium hydroxide solution pH 13 is almost reached.

• E4.10. A model experiment as a medium for the car battery

  Problem: The car battery should first be observed in a car and its function may be discussed. The model experiment reproduces the processes of charging and discharging and the reaction of the lead electrodes. Text books or transparencies can be used to explain these processes.

  Material: Beaker, transformer, voltmeter, electromotor (2 V), cable and alligator clips; two newly sanded lead plates, sulfuric acid solution (20%; C).

  Procedure: The beaker is to be half-filled with sulfuric acid solution. Both lead plates are to be positioned and attached in a way that they do not touch each other, they are to be connected to the transformer by cables (see Fig. 4.3). A direct current voltage has to be set so that a generation of gases can be observed for one minute. The transformer is to be removed. The voltage between the two plates is to be measured; the electromotor is to be attached.

  Observation: During the current supply a dark brown substance forms on one of the lead plates (as it can be observed on one plate of a battery cell in the car battery). After taking away the current supply a voltage of 2 V can be measured between the two plates. The attached electromotor first spins fast, but becomes slower and slower and finally stands still.

  Please note: The sulfuric acid solution is contaminated with lead sulfate and therefore toxic. If possible it should be poured into a labeled container, stored and reused for the same experiment. Otherwise it needs to be disposed off in the container for heavy metal waste.