Physical and Chemical Changes

Purpose: The goal of this laboratory is to learn the difference between physical and chemical changes in elements, and mixtures. This is a very important, and fundamental concept that any chemist needs to know, because most experiments are subcategories of these two groups of changes. We will test various elements and compounds, such as sulfur, and salt, for their physical and chemical properties. First, we will observe the physical properties of the substances, then we will conduct several experiments to see how these substances act by themselves, or with other substances.

Data and Calculations: This is the data that I have collected while observing the physical properties of the various substances presented for testing.

Substance + Formula	Physical State	Color	Effect of Magnet
Sulfur, S	Solid	Yellow	None
Iron filings, Fe	Solid	Brown-Black	Greatly Attracted
Sodium hydrogen carbonate, NaHCO3	Solid	White	None
Sodium chloride, NaCl	Solid	White	None
Sand, SiO2	Solid	Light tan	None
Magnesium, Mg	Solid	Silvery-gray	None

This is the data that I have collected while conducting the various tests that my lab book suggested.

System	Observations
Fe + S mixture tested with a magnet	Separates Fe from S cleanly; the Fe is attracted to the magnet while the S stays at the bottom.
NaCl and SiO2 mixture mixed with water	The NaCl dissolves in the water, and the SiO2 does not, which leaves the SiO2 at the bottom of the test tube.
Mg burned in air	Created an extremely bright, small flame. The combustion product is bright white, retains some original shape of the reactant.
Mg reacted with 6M HCl	The Mg bubbles violently in the liquid, producing immediate and intense heat. The Mg is dissolved completely.
Combustion product (cp) reacted with 6M HCl	The cp slowly clouds the liquid, producing some warmth gradually. After the lengthy process is finished, the liquid is still very cloudy, and there is some residue on the bottom of the vessel.
NaHCO3 reacted with 6M HCl	Very violent bubbling is produced by the reaction. The NaHCO3 quickly runs out of HCl to react with, so more is added. A drastic drop in temperature can also be observed.

Analysis:

1) Questions:

a) Mixing Fe and S is a physical change, since no reaction occurred, and the elements were very easily separated with a magnet.

b) Mixing salt, sand, and water was also a physical change. The sand did not change at all, except for becoming wet, and the salt simply dissolved, which is a physical change, since it can be easily extracted from the water via evaporation.

c) Burning Mg is a chemical change, since the Mg reacts with O₂ in the air to create a product whose properties are different from either.

d) Mixing Mg and the combustion product with HCl is a chemical change, since the process emitted heat energy and gas, which a physical change could not have accomplished. Mixing the combustion product with HCl is both a chemical and a physical change, since only some of the substance reacted with the HCl. This is evident, because on one hand it emits some heat energy, but on the other, it is clear that some of the substance remains unchanged because of the residue that is left in the vessel.

e) Mixing NaHCO₃ with HCl is most definitely a chemical reaction, since, first of all, it creates gas, and second, it uses energy to react.

2) If the property of the substance can be easily distinguished with the senses, or by changing the state of the matter, it is a physical property. If it involves destroying the substance and creating another, then it is chemical.

3) Deciding whether an observed change of matter is a physical or chemical change can be done by looking at whether the process uses or emits energy, whether a new and different product is created by the process, whether the process creates more, less, or the same amount of products, and whether or not the product is easy to separate.

4) The law of conservation of mass states that the mass of the sum of the reactants must be equal to the mass of the products.

Results/Discussion: From all my data, I have discovered that it is easy to separate iron from a non magnetic substance with a simple magnet, that you can free anything from salt by pouring water over it, and that Magnesium, Hydrochloric acid, and Sodium hydrogen carbonate interact with each other in specific ways. My answers generally make sense, because whenever I did whatever the lab book suggested, I always came up with an interesting, unique answer. The only doubt I have is the way that the magnesium combustion product reacted with HCl. I presumed that it would not react with the HCl, because it had already reacted with oxygen. However, a small, slow reaction did occur. This may have been because the magnesium did not react completely with oxygen, but left some parts not oxidized. That way, the magnesium areas could react with the HCl. Some errors could have included a thickness of glass issue, such that the magnet could not attract the Fe filings inside of the vessel. Also, the magnesium combustion product may have dispersed in the air due to its lightweight mass. Thus, one of the experiments would not have been possible to complete. The purpose of the lab was definitely accomplished, because the lab clearly defined the difference between a physical and a chemical change or property. It showed that a physical property is something that can be observed without destroying the original composition of the substance, and that can be easily measured with the senses, and that to see a chemical property, one must change the original substance by reacting it with another to create a whole new substance. This fact will help me very much in the future, because now I can clearly define between the two terms, and show the difference between them.