Introduction to Chemistry
Chemistry is the science that is concerned with the composition, structure and properties of matter. All of the objects we encounter on a daily basis, including pens, blankets, and refrigerators, and things we encounter in nature such as plants, animals, streams, and rocks are different forms of matter. Since chemistry as a science, deals with most of the objects we encounter on a daily basis, it’s difficult to exaggerate the influence chemistry has on modern science, technology and our ideas about our surroundings.
For thousands of years, humans have used materials to create useful products. The discovery of fire allowed early humans to observe the changes rocks and minerals undergo when exposed to high temperatures. By 1000 BC, observations led to the development of ceramics, glass, metals and other materials. They began to extracted chemicals from plants to create perfume and for medicinal purposes; rendered fat into soap and created alloys like brass (copper and zinc).
Early civilizations also practiced the art of fermentation and created beer and wine. Fermentation is one of the original chemical processes discovered during ancient times. A simple enzyme in yeast allows for the catalytic conversion of sugars into alcohol. Varying the amount of sugar, length of fermentation and the temperature at which the reaction proceeds all have noticeable impacts on the flavor of the alcohol. Even today, ethanol, acetic acid (vinegar) and penicillin are all produced by fermentation.
Chemistry certainly has ties with the development of these early technologies; however, as a field of study based on scientific principals it wasn’t until the latter part of eighteenth century that it came about. Original chemists began to record the precise quantities of substances they used in their experiments. From their work the central principle of chemistry came about: the materials surrounding us are made of infinitesimally small particles known as atoms and the arrangement of these particles into compounds account for the characteristics of materials around us.
Dalton’s Atomic Theory
The Atomic theory of matter, which is the basis of modern chemistry, was a product of the work performed by a British chemist named John Dalton. Dalton was a scientist throughout his life and maintained an interest in the science of weather and climate. These interests led Dalton to study the atmosphere and speculate on its fundamental structure. This eventually led to his atomic theory of matter. There is currently a very large and ongoing debate in the world of atmospheric chemistry on whether or not the earth’s climate is being affected by human activity. Atmospheric chemists concern themselves with the chemical processes associated with the atmosphere. We’ll talk more about John Dalton and his atomic theory, because it’s the cornerstone for modern chemistry.
A Scientific Approach to Problem Solving
Whether we know it or not, we use a scientific approach to problem solving every day. It allows us to make an observation, propose a solution to a problem with an explanation or hypothesis, and decide which solution is the best through experimentation. For instance, consider that your father asks you to cut the grass but your lawn mower isn’t working. A simple explanation for why it’s not working is because it doesn’t have any gas. You check the gas tank; find it empty therefore you’ve found the solution to your problem.
Similar types of experiments are the heart of chemical research. Experiments are observations of natural phenomena carried out in a controlled manner so that results can be duplicated and explanations about the phenomena can be made.
If a regularity or relationship can be drawn from the results we can state it simply as a law. A law is defined as a concise statement or mathematical equation about a fundamental relationship or regularity of nature. A good example of a law is the conservation of mass that states the mass or quantity of matter remains constant during a chemical change. The conservation of mass as we will learn throughout this course, is an extremely important relationship.
A hypothesis is a tentative explanation for some regularity of nature. A hypothesis has yet to be proven in a laboratory. Once a hypothesis passes many tests it becomes known as a theory. Therefore a theory is an explanation or hypothesis that has been proven through testing. A good example is the molecular theory of gases. This theory states that gases are composed of very small particles called molecules. This is a theory that has passed many laboratory tests and has become an acceptable model for explaining the behavior of gases (http://en.wikipedia.org/wiki/Kinetic_theory).
It’s important to note that a theory cannot be proven absolutely. Even gravity is only a theory, though I wouldn’t recommend jumping off a tall building any time soon to challenge it. The physics of motion, as devised by Sir Isaac Newton, held true for two centuries until it was discovered that his equations do not hold true for objects moving close to the speed of light. Later physicists were able to show that Newton’s equations didn’t hold true for very small objects either. These two discoveries led to a revolutionary developments in physics. The first led to the theory of relativity, the second led to quantum mechanics, the latter of which had a major impact on the field of chemistry.
Scientific Method
The scientific method provides us with an overview of the way we make observations about natural phenomena and then formulate theories to summarize them. We first formulate a question about a specific observation. The question can be something as simple as “why is the sky blue?” or as complex as “Why do objects defy Newton’s laws when traveling near the speed of light?”
The second thing we do is to try to formulate a hypothesis. Remember a hypothesis is a tentative explanation for some regularity of nature. Einstein theorized that the reason objects defy Newton’s laws of motion when traveling at the speed of light was due to what he called “general relativity.”
Third, we must conduct experiments to prove or disprove our hypothesis. Considering that the consequences of Einstein’s theory of relativity would upset nearly two centuries of experimental tests, his theories obviously needed to be proven. Ultimately three classical tests were proposed by Einstein to prove his theory of relatively. Unfortunately, they are beyond the scope of this lecture, but interested students should do further reading to satisfy their curiosity:
If interested, start here: http://en.wikipedia.org/wiki/Tests_of_general_relativity#Classical_tests
Finally, once a hypothesis is proven by experimentation we can officially call it a theory. What follows generally, is more experimentation to see if our theory holds up. Needless to say, Einstein’s theories held up under the tests he proposed and now have become widely accepted in the physics community.
Law of Conservation of Mass
In order to understand the law of conservation of mass lets first consider the difference between mass and matter. Matter is anything that occupies space and is composed of particles known as atoms. Matter can also change states and should not be confused with mass which is a conserved quantity. This means mass has a value that is unchanging in time. We can therefore define mass as the quantity or amount of matter in an object.
Antoine Lavoisier was a French chemist and considered to be the father of modern chemistry. When doing lab work, Lavoisier insisted on the use of the balance during chemical research. He weighed substances before and after a chemical change took place and lo and behold the mass remained constant throughout the duration of the chemical reaction. Thus, Lavoisier demonstrated the conservation of mass. The law of conservation of mass states that the total mass remains constant during a chemical change or chemical reaction.
Lavoisier was able to use the conservation of mass in order to determine what takes place during a combustion reaction. He was able to show that when a material burns, a component of air, oxygen, combines chemically with the material. For example, liquid metal mercury when heated in the presence of oxygen burns or combusts to form a red-orange substance, known as mercury (II) oxide. An oxide is a chemical compound that contains oxygen and one other element. We’ll talk about oxides again later on when we learn more about chemical compounds. Many other elements beside Mercury can form oxides.
Example of Conservation of Mass
Lavoisier heated the red-orange substance, known as mercury (II) oxide and was able to decompose the mercury oxide back into the original compounds mercury and oxygen. Using the conservation of mass principles, let’s determine the amount of air or oxygen present in the product formed by the combustion of 3 grams of mercury which forms 3.24 grams of mercury oxide.
We want to determine the mass of oxygen that reacts with mercury. If we strongly heat the red-orange substance it will decompose back to mercury and oxygen. Thus we are trying to determine the mass of oxygen released when we heat the substance.
Considering the conservation of mass states that total mass remains constant during a chemical reaction, the amount of oxygen it takes to form 3.24 grams of mercury oxide can be deduced easily. Subtract 3 grams of mercury from 3.24 grams of mercury oxide and the amount of oxygen present must be 0.24 grams.
Mass vs. Weight
The terms mass and weight are often used interchangeably which is incorrect; there is a distinction between the mass and weight of an object. The weight of the object is the measure of the force of gravity on the object. It is proportional to the mass of the object divided by the square of the distance between the center of the earth and center of mass of the object. The mass of the object is a conserved principle, meaning it never changes; however, an objects weight varies depending on its distance from the center of the earth.
Conclusion
In conclusion, chemistry is an important science. Since it is the science deals with most of the objects we encounter on a daily basis, it’s difficult to exaggerate the influence chemistry has on modern science, technology and our ideas about our surroundings. A scientific approach to problem solving is something we as humans do inadvertently every day. The scientific method approach is a cookbook approach that a chemist or scientist uses in problem solving. Lastly, we talked about the conservation of mass, which states that the total mass remains constant during a chemical change or chemical reaction.
This first video lesson offers an introduction to chemistry, the scientific method and the conservation of mass: