Chemistry: A key tool for sustainable development

This year the slogan of the Science Fair embraces very diverse concepts. Of these, the Institute of Chemical Research has chosen to focus on Climate Change, and how the use of Chemical Technologies are an essential tool to combat this serious problem. To this end, a series of very visual practical experiments will be carried out to illustrate how Chemical Science works.

These experiences have been divided into two main blocks: the first is to teach that in order to combat Climate Change it is necessary first to understand its principles, and how Chemistry helps us in this task. The second block provides some basic examples with which we will better understand how chemistry favors scientific, technological and social progress based on the principles of sustainable development.

1) The fundamentals of Chemistry: Understanding Climate Change.

Chemical reactions.

Gold Rain: In this experiment the crystallization of the lead iodide (PbI2) is presented. Begin by preparing the lead iodide as a yellow amorphous powder. The lead iodide dissolves in hot water, generating a colorless solution (since the cations Pb2 + and I- have no color), and when cooling the solution the product crystallizes, forming the rain of small yellow crystals that are kept in suspension. When a light beam is passed through the solution, it is reflected and diffracted by the crystallites, which produces the illusion of a golden shower.

Invisible Inks: Invisible inks or sympathetic inks allow you to hide written texts, which are only accessible to the reader who knows the secret procedure that makes visible their presence. In this experiment one takes advantage of the properties of the salts of certain metallic elements, which form colored complexes when reacting with certain organic substances. A well-known example of such reactions is the formation of Prussian blue dye.

Luminescent reactions: Chemical reactions involve not only changes in the state of matter, but energy exchange. Usually these exchanges involve the release or absorption of heat, but also sometimes they can mean the production of light. Chemiluminescence occurs when a molecule in an unstable electronic state emits light as it relaxes to return to its ground state.

Oscillating Reactions: A reaction is said to be oscillating when, after completion, the system returns to its initial state and the reaction starts over again. This is a surprising demonstration of the ability of some chemical systems to organize spontaneously and lead to regular patterns that recall the behavior of living beings. The particular example that we are going to see is the reaction of Briggs-Rauscher (BR). In this case, three colorless solutions are mixed in a flask and pass through 15 or more cycles from colorless, amber, to blue-black, before finishing. Between all the known oscillating chemical reactions, this is perhaps the most impressive.

The states of matter.

Crystallization: An experiment is performed on the crystallization of double salts (alums), which produces colorful crystals of different shapes, colors and sizes. The experiment allows us to discern some of the nucleation and crystal growth stages, as well as the facets of the crystals, which reflect the inner structure of the crystal.

Chemical Gardens: Colloidal solids are non-crystalline structures that possess important properties, such as selective permeability. The chemical garden is an experience in which this property is used to generate three-dimensional structures that grow before the eye in a manner similar to how plants do, even if they are non-biological beings. It is part of a solution containing sodium silicate, which is seeded with crystalline particles of salts of different colors. Immediately, a chemical reaction occurs which surrounds the crystals with a metal silicate membrane completely insoluble, but permeable to the ions present in the solution. These penetrate the inside of the membrane, increasing the internal pressure and causing the particle to increase in size (osmotic pressure). The combination of this growth with convection causes tubular structures to grow toward the surface, occasionally projecting lateral “branches”. These effects are analogous to those regulating the growth of living cells, since the cell membranes are also semipermeable.

Climate change.

Greenhouse Effect: Combustion of coal, oil, natural gas and other fossil fuels for power generation is steadily increasing the atmospheric content of carbon dioxide. CO2 is transparent to visible light, but opaque to infrared radiation. In this way, it exerts in the atmosphere an effect similar to that produced in greenhouses, increasing the average temperature of the planet. In the near future, this rise in temperature can have catastrophic effects on climate, ecology and human society. In this experiment, this property of CO2 is practically demonstrated, illuminating two flasks in which a piece of dark material that simulates the behavior of the Earth has been placed, absorbing visible light and re-emitting it in the infrared. By pouring gaseous CO2 (generated before the audience by reacting sodium carbonate with vinegar) into one of the flasks, the heating of the dark part is accelerated, because the infrared light, which can not leave the vessel, is transformed into heat.

2) Chemical Technologies for Sustainable Development.

Chemical Volcano: Catalysis is an important phenomenon through which certain substances induce a chemical reaction, apparently without participating in it. An everyday example of catalysis is the decomposition of oxygenated water by the iron that is present in the blood. This reaction releases oxygen, which acts as an antiseptic. This experiment shows the catalytic decomposition of hydrogen peroxide in a very spectacular way, which simulates a “volcano”. Catalysis is one of the most powerful tools we have to control chemical reactions, making them cleaner and more selective.

Polymers.

Flubber: Flubber or slime is formed by mixing a solution of a polymer, polyvinyl alcohol (or PVA), with a solution of borax. The borax binds the PVA strands and a cross linking occurs. In other words, PVA molecules resemble long spaghetti. When Borax (sodium tetraborate) is added, it is responsible for joining the PVA molecules together, as does the melted cheese with the spaghetti, increasing the consistency of the whole.

Nylon Manufacturing: The fibers formed by their more immediate derivatives are known as nylon. The nylon can be tinted easily, possesses hardness and toughness, and resists molds, enzymes and moth. Among its applications, apart from the textile industry, it is worth mentioning its use in obtaining objects such as brushes, carpets, gears, bearings, bicycle wheels … In this experiment a nylon fiber is obtained by reacting two solutions, each one containing one of its basic components. As both solutions are immiscible, the polymerization will occur only at the interface (contact zone) of the two liquids.

Renewable energy.

Batteries with fruits: The object of this experiment is to show the generation of electric energy by simple means. Zinc and copper electrodes are inserted into fruit pieces, and are connected to a condenser. The electric charge that it acquires is used to drive a small electric clock, so that the time that it marks is proportional to the electrical work done by the battery. The chemical work is not carried out by the fruit, but by the chemical reaction that implies the metal of the electrodes. So this technique does not allow the sustainable production of electricity. The following example illustrates a more practical generation method.

Fuel Cell: Fuel cells are devices that allow you to convert chemical energy into electrical energy with great efficiency. The fuel cells may be reversible, i.e., they may also be used to store electrical energy in the form of chemical energy. This possibility would allow the use of certain chemical substances as energy vectors, ie as means to transport the energy from where it is produced (eg a power station) to the point of consumption (such as a car). One of the future energy vectors is hydrogen. In this experiment the generation of hydrogen with electricity is illustrated, and later how it is regenerated from the hydrogen that has been produced. For this, a very simple electrochemical cell is constructed, using a saline solution that makes electrolyte, and pieces of metal scouring pad that make the electrode. When connecting a battery to the system, the electric current decomposes the water, producing hydrogen, which is deposited in the form of small bubbles attached to the surface of the pad. When the battery is replaced by a capacitor, the process is reversed and it is charged with electricity. The electric charge is determined using a small electric clock, as described in the previous experiment.