Sunday, September 27, 2015

Week 2 Blog

Ariana Trossen
5th hour SG Chem 2
Dr. Finnan

     This week in class we dove deeper into chemistry by looking at the history of it. We discovered how chemistry began by learning about the different scientists who had a hand in its foundation. From Empedocles to Democritus to Dalton, we learned about what people believed about the things around us are made of. We also studied Joseph Priestley's discovery of oxygen and Antione Lavoisier's theft by taking the credit. Something I didn't know before was that Napoleon Bonaparte loved science more than war and because of this it led to a competition between Humphry Davy and Joseph-Louis Gay-Lussac. After looking the history of chemistry, we studied the ratios of the masses of elements in a compound and their equations. Then we applied the ratio of the masses of elements in known compounds and made inferences on their compositions. Last week we learned all about atoms, elements, particles, and compounds, but people didn't always know about them.
     Empedocles was a Greek philosopher and scientist, he proposed the first theory about what the things around us are made of. He said that all matter was composed of four different elements: fire, air, water, and earth. However, there were many flaws in this because no matter how many times you break something it never ends up as one of those elements. That led to other scientists drawing different conclusions.
     Democritus was also Greek, though unlike Empedocles, his new theory for what things are made of was based on reasoning rather than science. He believed that if something, a stone for example, was cut in half again and again until it couldn't be anymore, then you would end up with these microscopic pieces, which he called "atomos", "Atomos" means invisible, the pieces that make up the stone are so small they can't be seen with the naked eye. His idea was dismissed at first, but later became the foundation of what we know today.
      Joseph Priestley began to experiment with red mercury calx. He discovered that when it is heated it breaks down into two different substances: liquid mercury and a strange gas. Priestley went further by collecting the gas in jars and studying it. He ran some tests with it, discovering that it made flames burn stronger and allowed a mouse to live longer with it than "normal air." Dephlogisticated air is what Priestley decided to call it, but it didn't stick.
   After hearing about Priestley's discovery, Antoine Lavoisier had to perform the experiments himself. He did and decided to rename the strange gas oxygen. Lavoisier went on to discover hydrogen and many other elements as he continued to experiment. He was very technical and weighed everything. This led to Lavoisier establishing the Law of Conservation of Mass: mass cannot be created or destroyed. More and more discoveries were being made on what matter is.
     John Dalton put the pieces together and formed a modern atomic theory with four main concepts. These concepts were: 1) All matter is composed of indivisible particles called atoms. 2) All atoms of a given element are identical; atoms of different elements have different properties. 3) Chemical reactions involve the combination of atoms, not the destruction of atoms. 4) When elements react to form compounds, they react in defined, whole-number ratios. Dalton gave structure to the ideas people and scientist were experimenting on.
    Humphry Davy and Joseph-Louis Gay-Lussac were rivals, and they were quite opposites. Davy was flamboyant, charismatic, loved leisure, and spent time on many different hobbies. Gay-Lussac was patient, careful, fully devoted to science, and spent time with his family when he wasn't working. Davy discovered sodium and potassium, and after he did so Gay-Lussac and himself raced to discover as much as they could about the new elements. When a strange substance that formed black crystals and could produce a purple vapor was found in seaweed, Gay-Lussac was asked to review and perform the scientists who found it's experiments. He decided to call it "iode," which means purple in Greek, due to its purple vapor. He had no idea that Davy had been told about it and started experimenting as well. Another competition began between them. Gay-Lussac beat Davy to the press by one day with the result that what is called iodine today is an element itself and not composed of chlorine as they suspected at first. There are many different elements, about 116 known today, and they all have their own unique properties.
     By looking at the ratio of the masses of a compound, we drew out different particle drawings and equations to represent the compound. One hypothesis was to draw out the atoms with them having the same mass. The second hypothesis was to draw out the atoms with one being heavier than the other based on the ratio. As a class we determined that the second hypothesis was the better option because it made more sense based on our learning from Dalotn and others that every element has different properties and therefore different masses. After this we applied the ratio of masses of compounds to compare unknown compounds with a known compound. These images below show how we calculated the ratios and percentages, and how we determined if the unknown compounds matched up with the known compound, in this case sucrose.

  





















     As we learned new things each day in class this week, it all built on each other. Starting with Empedocles and ending with what we know today by studying compounds and their chemical equations. Each scientist provided a stepping stone for the next as they made their discoveries. By looking at what the previous scientists found and experimenting on new ideas and making inferences, we were able to apply what we've learned from these scientists, who gave chemistry its foundation, to learn about different elements and compounds and how they relate.
     One question I still have is: what is the Law of Definite Proportions? We didn't have quite enough time to cover it in class, and I'm interested to know how it relates to the comparing of known compounds to unknown compounds.

Saturday, September 19, 2015

Week 1 Blog

Ariana Trossen
5th hour SG Chem 2
Dr. Finnan

This week in class we reviewed classification of matter and techniques for separating compounds and mixtures, and we learned some new information, such as, Avogadro's hypothesis. While reviewing classification of matter, we looked at the difference between atoms, particles, and molecules. Atoms are the individual building blocks of particles and molecules. A particle is any single atom or multiple atoms chemically bonded together. A molecule is two or more atoms chemically bonded together. We went further after this to compare pure substances, mixtures, elements, and compounds. A pure substance is any combination of a single type of atom or molecule. A mixture is a combination of different types of atoms and/or molecules. Elements are combinations of a single type of atom, they can be individual or chemically bonded together. A compound is a combination of different types of atoms chemically bonded together. All elements and compounds are pure substances. Compounds and mixtures can be separated, but not in the same ways. Mixtures can be separated physically, such as with a magnet or by filtering, but compounds have to be separated by chemical means because there are chemical bonds to hold the atoms together, ways to do this include electrolysis and decomposition. We went on to learn about Avogadro's hypothesis, which states that with two given samples of an ideal gas, of the same volume and at the same temperature and pressure, contain the same number of molecules. This makes it possible to find the formulas of compounds formed when gases react.226 In some cases we found that in order to keep the mass the same the molecules of some gaseous elements have to have two atoms. An example of this is when hydrogen and chlorine react to form hydrogen chloride.



An experiment we did in class was with sugar cubes to see how they would react when placed in water, ethanol, and a 50/50 mix of water and ethanol.
In this experiment we discovered that the sugar cube dissolves completely in water, not at all in ethanol, and not quite completely in the 50/50 mix and also at a slower rate than in pure water. After doing the experiment we white boarded out particle drawings of the before and after for the sugar cube placed in water and the sugar cube placed in ethanol.


All these things we learned this week are connected. We started from the beginning with the basics of how matter is classified. Atoms are the building blocks of molecules and both an atom and a molecule are considered particles. Then we have atoms and molecules that make up pure substances, mixtures, elements, or compounds. A mixture is different molecules and/or atoms mixed together. A pure substance is any single type of atom or molecule. An element is any atom or molecule made up of a single type of atom. A compound is any type of molecule made up of different atoms chemically bonded together. Elements and compounds are both pure substances. Then we expanded by talking about how compounds and mixtures are separated. Compounds have to be separated by chemical means, which we were showed in the experiment of separating water molecules. This also proved that water is made up of two hydrogens and one oxygen. Mixtures, however can be separated by physical means, which we were showed when a magnet was used to separate iron from a mixture with sulfur. Avogadro's hypothesis ties into this as we learned to draw out the formulas for how elements react and form compounds with particle drawings. I feel we learned a lot this week and am excited to further my knowledge and understanding of chemistry.