7.1.3: Useful Materials From Chemical Reactions
(synthetic, natural resource, concentration)
How Are Useful Materials Synthesized?
Chemical reactions occur naturally all the time, all around us. These chemicals have different properties depending upon what they are made of. Some of the existingnatural chemical products are helpful and beneficial to us; some are not. Humans would like to make more of the natural chemicals that are useful and make new chemicals with new properties that are even more useful than natural ones. Chemicals that are made by humans are called synthetic materials. If you have carried out chemical reactions in a class laboratory, then you have synthesized materials.
Some naturally occurring chemicals are beneficial, but are not very common. We say that these exist at low concentrations. The concentration of a material is fraction of the amount of that particular material divided by the total amount of all the material it is part of. For example, rubber is a very useful material, but it only forms naturally from the sap of a rubber tree. Chemists can recreate the chemical reactions that make rubber. They can create synthetic rubber at very high concentrationsto meet human needs.
Useful materials are synthesized from natural resources. Natural resources, found in nature, can be pure elements, simple inorganic molecules, or complex organic molecules. Chemists then assemble them in an ordered set of steps, chemical reactions, to create the desired synthetic material. The process is entirely repeatable – it can be replicated at a later time or by another lab. Just the way you would build a house one brick at a time, a chemist synthesizes a material by adding molecular “blocks” one step at a time. You build the house by moving the blocks into place by hand. Chemicals are too small, so the chemist relies upon chemical reactions to move molecules into place.
It is important to remember that while compounds can be synthesized by chemical reactions, the atoms of elements themselves cannot. The only way for one element to change into another is by nuclear reactions such as fission or fusion. With fission, atoms are split; with fusion, they are smashed together. These nuclear reactions either involve a great deal of energy, such as within nuclear bombs, or occur slowly in nature, such as through radioactive decay. For centuries, chemists (known as alchemists) tried to turn inexpensive elements such as lead into valuable elements such as gold. They were never successful.
[Photo idea: (1) show a kid with legos or blocks and (2) a photo of a chemist in a lab with the inset of a polymer chain – “How is a child building with blocks like a chemist synthesizing chemicals?”]
What Forms Do Synthetic Materials Take?
Most of the objects we encounter every day involve synthetic materials. Look around you. The paints and varnishes you see on objects are synthetic. Look at the clothes you are wearing; if they are nylon, rayon, polyester, etc., they are synthetic. Look at the list of ingredients on packaged foods; it likely includes several synthetic chemicals used for preservatives. However, it is likely that the fruits and vegetables in the food were grown using synthetic fertilizers. There is no end to the possible combinations of atoms in synthetic materials. The catalog of a chemical company might list more than 40,000 chemicals that you could buy.
One of the most common forms of synthetic materials is that of polymers. Polymers are large molecules, often long chains, that contain repeating subunits, called monomers. So, the composition of a polymer can be very simple, but the molecules can be huge, containing millions of atoms. Polymers occur naturally, and have been used by people for centuries. They include wool, silk, rubber, and cellulose. Polymers have many different but important properties, such as strength, flexibility, and elasticity. These and other polymers that don’t occur naturally are synthesized in large volumes to provide clothes, building materials, and most of our material goods.
The most common synthetic polymers are plastics. Plastics are moldable substances that are strong but flexible. They are organic polymers, based on long chains of carbon atoms that often have other atoms of oxygen, sulfur, or nitrogen included as well. Plastics are usually made from the natural resource of petroleum, pumped from the ground. Plastics come in many different forms, which are shown by the different plastic recycling numbers on cartons and bottles. Plastics are generally very resistance to breaking down and degrading. However, they can be synthetically designed to be biodegradable.
[Photo idea: Show a photo of liquid plastic being poured into a mold. Then show a photo of plastic displaying its properties of being both flexible and strong. Perhaps show a kid bending a milk carton to demonstrate how flexible it is, and then show the same kid hanging from a pole by the handle of the milk carton (with the bottom of the carton cut away so that the carton can be fit over the pole).]
How Have Synthetic Materials Affected Society?
Synthetic materials allow very large numbers of people to be clothed, housed, and fed. The large cities of the developed world could never exist without synthetic materials. For example, most foods rot or decay very quickly without synthetic preservatives and plastic packaging. Synthetic materials allow cars and trucks to be lighter in weight but stronger in case of collision than if they were just made of metals. Paints and sealants allow wooden buildings to last much longer than they otherwise would. Here are some areas where synthetic materials have been especially important:
Synthetic Fibers Your clothes are likely made of many different kinds of synthetic fibers, like acrylic, nylon, polyester, spandex, and rayon. Different naturally occurring fibers like cotton, wool, and silk have been used for thousands of years and different qualities, but they can be expensive and only grown or raised in certain parts of the world. Synthetic fibers can be designed to replicate these or have many other characteristics, and are generally much less expensive. They last longer, dry quicker, and clean easier, though they will burn more easily than natural fibers.
Synthetic Fertilizers When crops are grown in soil, the plant roots remove nutrients from the ground, such as nitrogen, phosphorous, potassium, calcium, magnesium, and sulfur. Over time, the fertility of the soil will decrease unless these and other nutrients are added back into the ground in the form of fertilizers. The world now spends more than $100 billion on synthetic fertilizers that provide plants with the nutrients they need in forms that the plant roots can absorb. These fertilizers can even be made into pellets with polymer sealants so that the fertilizer is released slowly over time.
Synthetic Fuels One day, the world will run out of petroleum. Cars and trains can run on electricity, but how will be power planes and boats? Synthetic fuels of many kinds can be made through chemical reactions. The starting resource can be plant residues, animal oils, coal, algae, or other materials. Some of the chemical reactions create gases as an intermediate step, called syngas; some directly create liquid fuels.
Synthetic Medicines If you have ever taken medicine for an illness, you have likely benefitted from medicinal chemical synthesis in the form of pharmaceuticals. Many synthetic chemicals that have been developed are used to cure or reduce the effects of diseases and illnesses. Many medicines are discovered in nature – plants and animals produce many different chemicals that protect them from attack by bacteria, fungi, and viruses. Chemists can determine the chemical formula of these natural medicines and then produce them in large volumes through chemical synthesis.
[Photo Idea: not very creative here, but perhaps a montage showing 4 scenes – synthetic fibers, synthetic fertilizers, biofuels, and synthetic pharmaceuticals.]
Assessment
- a. ContrastWhat is the difference between the structure of monomers and polymers?
b. CCC Describe how the structure of polymers could help them to make very strong materials.
- a. SEP Gather and make sense of information to describe that synthetic fibers usually come from petroleum resources.
b. Describe Why is chemical synthesis most important when natural concentrations of a substance are low?
Study Guide
1.3 Useful Materials from Chemical Reactions
How Are Useful Materials Synthesized? Useful materials are synthesized by chemical reactions, usually starting with natural resources and occurring over many steps.
What Forms Do Synthetic Materials Take? There are thousands of different kinds of synthetic materials, often in the form of polymers like plastic, that have a range of unique material properties.
How Have Synthetic Materials Affected Society?Synthetic materials are used in all aspects of our lives and include synthetic fibers, fertilizers, fuels, and medicines.