In this lab, we held an orange peel and some red and green apple peels near a Bunsen burner flame to see what would happen. When we held the orange peel near the flame and squeezed there was a sharp yellow/whitish flame and when we did the same with the apple peels there was an orange and purple flame (sodium and potassium present). Ethene (ethylene) was also present in the lab. The compound ethene, is organic which means it is a molecular compound of carbon. The opposite of organic compounds are inorganic compounds which are not based on molecular compounds of carbon. Ethene is apart of a specific class of organic compounds called hydrocarbons. Like the name, hydrocarbons are largely made up of hydrogen and carbon. Hydrocarbons have intramolecular covalent bonds. When a hydrocarbon burns in the presence of oxygen, combustion happens (combustion basically means fire).
The chemical formula from burning the fruit peels:
C2H4(g) + O2(g) —- CO2(g) + H2O(g)
The C2H4 + O2 are called the reactants and the CO2 +H2O are called the products. The reactants are turning into the products. The reactants have a total of 2 C atoms, 4 H atoms and 2 O atoms. The products have a total of 1 C atom, 2 H atoms and 3 O atoms. This is a violation of the law of conservation of mass. The law states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants entering into the reaction. In simpler terms, the reactants total mass must equal the products total mass. We cannot change who the product is but we can change how many/amount. If we add coefficients we are changing the number of that atom not the molecular formulas. In order to balance this equation, we must add a 2 in front of the CO2 and the H2O and we must add a 3 in front of the O2.
C2H4(g) + 3O2(g) —- 2CO2(g) + 2H2O(g)
Now the reactants have a total of 2 C atoms, 4 H atoms and 3 O atoms and the products now have a total of 2 C atoms, 4 H atoms and 3 O atoms. Both sides are now equal.
In this lab, we took 5 wooden splints soaked in different solutions and held each one separately over a Bunsen burner to see what colour the flame would turn. In simpler terms we performed a flame test. A flame test allows you to identify a metal from its characteristic flame color. Each wooden splint had a different color of flame. Why are they different colors? The color is the result of the electron structure of each solution. Each atom has a unique arrangement of electrons therefore each gives a unique color. An electrically charged atom or group of atoms that has a net charge are called ions. When we place the soaked wooden splint in the flame, metal ions are being placed in the flame and their electrons absorb the energy and move to higher energy levels around the nucleus. The light given off in the flame test is when these electrons fall back to their original level. The Bunsen burner flame gives the electrons heat energy and brings their energy levels higher and when they lower it gives off as light energy. Basically the change in energy levels represents the color of the light given off.
On Saturday we made slime! We mixed together polyvinyl alcohol, sodium tetraborate and food colouring. Then we observed the slime and did some tests to see what properties it had. A special characteristic the slime had was viscosity. Viscosity is a property related to the resistance of a fluid to flow (it goes against flow). The name of the slime we made was a polymer. A polymer is a macromolecule consisting of many similar small molecules. The molecules are covalently bonded together in a long chain.
As we know, PVA and borax combined result in a polymer, which has special properties. The slime acted like a solid and like a liquid. When we were observing, the slime acted like a liquid because it was a fluid and we could shape it easily into anything and it would be able to go back to the original form. However, like a solid, the slime was able to bounce on the table when we dropped it and it broke apart when we pulled it quickly out of the beaker.
The PVA and borax molecules in the solution formed cross-links. Cross links caused the slime to flow slower and change shape. The solution is an example of polymerization which is the formation of very large molecules from many smaller molecule units.
*Some other examples of polymers are: polyesters, nylon, polyvinyl chloride, polystyrene and natural rubber.
On Saturday we tested many different materials to investigate the different properties of each. We looked at the luster, tested for electrical conductivity, malleability, ductility and reactivity for each material. After gathering our results we then split the materials into a metal and nonmetal group based on their properties. From the start, we knew that the properties of wood and the properties of lead would be different but the tests confirmed it. Metals have specific properties different from nonmetals. Metals have luster, they are conductors of electricity, they are malleable, ductile and mostly somewhat reactive. Metals are able to be conductive, malleable and ductile because of metallic bonding. Solid metals have metallic bonding; the metal nuclei are in fixed locations but the electrons surrounding them can move freely. However, something like glass has electrons in fixed positions which are joined tightly because of covalent bonds so the glass does not conduct electricity. As we all have probably seen, metal rusts. This happens because the metal is reacting with oxygen. When metals are exposed to and react with oxygen it is called oxidation. Nonmetals have basically the opposite characteristics. They do not have luster, they are nonconductive, brittle and non ductile. The Period Table of Elements separates metals and nonmetals. What happens to the ones that don’t fit in either group? There is another group called metalloids. Some can be shiny or dull and some are semiconductors. Also there are some that are called alloys. Alloys are materials that contain more than one metal element and still maintain the characteristic properties of metals. For example, gold (a metal) is too soft for jewelers to work with so they make an alloy of gold, silver and copper. This combination is harder and will hold its shape, making it easier to work with.