100 Greatest Discoveries: Chemistry

Chemistry is a fascinating subject. So much information has been discovered, yet there is still so much more information to learn. Throughout history many groundbreaking discoveries have been made. It started back in ancient Greece. The Greeks thought there were only four elements: earth, air, fire, and water. Leonardo Da Vinci challenged that idea and said that air was composed of two different substances. This led to the discovery of oxygen. Joseph Priestley was searching for new air (gases). He conducted experiments with liquid mercury. Antoine Lavoisier also experimented with oxygen. Joseph Priestley discovered oxygen, but Antoine Lavoisier invented it. Next, the atomic theory was invented by John Dalton. He thought that everything was made of smaller pieces called atoms. Amedeo Avogadro quashed the assumption that gases were made of one atom. He suggested that atoms combine into molecules. The synthesis of urea was definitely mind-blowing. By combining inorganic elements, an organic element is created. This organic element is found in life. Perhaps this is the secret of life Victor Frankenstein used when creating his monster. August Kekule was an important chemist that thought that the chemical structure of an element was essential. Everyone thought that the structure of every molecule was a straight chain, but Kekule discovered that Benzene was shaped like a ring. Dimitri Mendeleev is one of the most genius chemists in history. He created the periodic table. This is the image that everyone associates with chemistry. It all started when he was trying to teach his class about different elements. He laid out cards for the different elements on his desk. The cards had the properties of the elements on them. Dimitri grouped the cards in rows and columns based on their similarities. Mendeleev was able to predict properties of elements that had not even been discovered! Next, Humphry Davy set the path for electrochemistry. He performed an experiment with potash. Electrochemistry is used everyday in the modern world. Some examples are the aluminum industry, rechargeable lithium batteries, and solar panels. Next, atoms were discovered to have signatures of light. When elements are added to fire, the color of the flame changes. Sodium changes a flame to orange. Copper changes a flame to green. Strontium changes a flame to red. Joseph Thompson made a revolutionary discovery about atoms. By using what he called a “crookes tube,” a stream of electrons was displayed. Thus, the electron was discovered. Gilbert Lewis then came up with the theory that electrons went around atoms as shells. When electrons were exchanged, new chemicals were formed. For example, sodium and chlorine on their own are toxic, but when combined, they produce everyday table salt. Soon, fullerenes were discovered. They are carbon nanotubes that are one-billionth of a meter in diameter. These are smaller than DNA! In conclusion, chemistry is constantly changing as new things are being discovered or proven.

Freezing and Melting Lab

Freezing and Melting of Water Based on Physical Properties

Problem: What is the freezing point and melting point of water?

In this experiment, a test will be done to determine the freezing and melting point of water. The independent variable is the temperature of water in the beaker. The dependent variable is the state of the water in the test tube. We will be filling a beaker with ice water and adding 5 teaspoons of salt. Then the test tube will be placed in the beaker. The temperature probe will remain in the test tube for the entire lab. After 15 minutes, the test tube will be taken out, and the beaker with be filled with warm water. After holding the tube for 10 minutes, the tube will be put into the hot water. This is to examine the changes in the state of water based on its characteristics.
 

This is how the lab was set up.

Hypothesis: The freezing point of the water in the test tube will will be at 0 ºC because it is one of the physical properties of water. The melting point of water will be at 25 ºC because that is when the ice will have enough energy and warmth to turn into a liquid.

Data and Results:

The water in the test tube was partially frozen on the edges of the water. It did not turn into a complete solid ice cube; however, there was some freezing.

During the melting phase of the water, the ice on the sides quickly melted into liquid after placing it in the hot water.

Freezing and Melting Points of Water

General Temperature of Water	Temperature (ºC)
Freezing Point of Water	0.4 ºC
Melting Point of Water	18.8 ºC

These are the freezing and melting points of the water in the test tube. These were based on the flat parts of the graphs below. The melting point was 18.4 ºC higher than the freezing point. 

This is graph shows the temperature patterns for the “Melting Curve” and the “Freezing Curve.” The Freezing Curve is red, and the Melting Curve is blue. During the beginning and end of the Freezing Curve the kinetic energy decreased because the temperature decreased. However, the part of the Freezing Curve that remained constant had a decrease of potential energy because the temperature still decreased. The beginning and end of the Melting Curve had a major increase in kinetic energy, especially the end because the temperature increased. The part that stayed constant in the Melting Curve had an increase in potential energy because the temperature increased.

Conclusion: In conclusion, this experiment was successful in helping me find out the freezing and melting points of water. My hypothesis for the both the freezing point and the melting point were rejected. I was only 0.4 ºC off on my hypothesis for the freezing point, but for the melting point, I was almost 6 ºC off. Some errors that may have occurred would be that we did not stir the temperature probe enough. Also, not all of the salt had dissolved because there were still little clumps stuck to the sides and the bottom. The information I collected can be used in many other tests, as well. The same experiment could be conducted, but instead of water in the test tube, another liquid could be substituted. An experiment can be done to compare the freezing and melting point of water to the boiling point of water. In conclusion, I learned a lot about the freezing and melting point of water, and this experiment has clarified the process of change from ice to liquid H2O.