Physical and chemical change

Hong Yu Lui
Wenzel Chem H
D period
Sep 13th, 2014

Lab report #1 on chemical and physical properties/ changes

Introduction Summary:

The purpose of this experiment is to allow students to understand how to differentiate physical and chemical properties and reactions of matter by observing changes of matters under circumstances. Physical properties are properties of matter that can be observed without changing the composition of the matter, including the volume, mass, color, density, and shape of it. Chemical properties include the matter’s flammability, acidity, and heat of combustion. It can only be observed through a chemical reaction. Chemical reaction is when the chemical identity of a matter is altered through reacting to another matter. There is a change in the arrangement of atoms. A lot of property changes during a chemical reaction too. Chemical reactions are also very hard to reverse. One example of chemical change is when sugar is combined with sulfuric acid. We can tell it is a chemical change because heat and bubbles are produced, and carbon was separated from the other substances. On the other hand, physical reaction only does macroscopic changes to the matter, for example, altering the shape, and painting the matter. There is not rearrangement of atoms in a physical change. Only a few properties change during a physical reaction, and they are mostly easy to reverse. One example of a physical change is mixing salt and water together. Although there is not a change in its appearance as they are all transparent liquids, the mixed salt and water can be easily separated again through boiling the mixture, making it a physical change because it is easily reversible.

Vocab:
1. Homogeneous means similar in kind, composed of the same kinds. Furthermore, homogeneous mixture means that the components of a mixture are evenly distributed and cannot be easily told apart. For example, salad is a homogeneous mixture because we can easily tell the components in it.
2. Heterogeneous means different in kind, composed of different kinds. Furthermore, heterogeneous mixture means that the components of a mixture are not evenly distributed throughout the mixture. For example, salt water is a heterogeneous mixture because salt and water cannot be visually told apart, salt is also evenly distributed in the water.
3. Opaque is when something is unable to be seen through. For example, a person is opaque because we cannot see through it.
4. Transparent is when something can be seen through. For example, glass can be seen through, we can see the other side of a glass through it.
5. Mixture is when two or more substances that are physically mixed. They are not chemically combined.
6. Compound is when two or more elements chemically combined, forming a substance. The elements are combined in a fixed proportion. For example, water is a compound. Two hydrogen atoms and an oxygen atom are chemically combined to form water, and the proportion of it is always 2 hydrogen atoms and 1 oxygen atom.
7. Elements are substances that contain only one kind of atom. It is the simplest form of matter and cannot be broken down into simpler forms in terms of chemical means.
8. Observation: Notes made out of only what can be seen, heard, smelled, felt, and tasted
9. Interpretation: Conclusions and explanations made from observations

Procedure:
Procedure as written in the handout with the following exceptions：
First, the magnifying glass was missing; therefore students were not able to observe the substances closely. Secondly, in procedure 4 of part B, put a stirring rod over the beaker with the mixture in it when it is being poured out. Thirdly, step 5 was added into part B: Place the filtered mixture onto the hot plate. Turn the hot plate to 10 and wait for the liquid to evaporate. Record your observations.

Data analysis:
1. Chemical or physical change
a. When iron and sulfur is combined, a physical change occurs. Only one property is changed after they are combined, which are the position of the two substances. It is also easily reversible as iron is attracted to magnetic and sulfur is not so it is possible to take out iron using magnets. There were not any changes in the color, temperature, and physical state. Therefore, we can conclude it is a physical change.
b. When sodium chloride, water, and sand is combined, physical changes occur. We know that it is a physical change because it is easily reversible. Sand can be filtered out through filtration; sodium chloride can be separated from water through evaporating the water. Other signs of it being a physical change includes that there were not a lot of properties that changed when the substances were combined.
c. When magnesium is burned in air, it is a chemical reaction. When the magnesium was burned, smoke was produced, suggesting that heat is produced. A bright light was also produced. The magnesium also turned from a bendable silver matter to a white powdery matter. A lot of properties of the magnesium were changed after burning it up. Therefore we can conclude that it is a chemical change.
d. When magnesium is reacted with 6MHCl, chemical change occurs. There were bubbles, smoke, and the temperature of the mixture increased rapidly. The bubbles meant that gas was being released from the mixture, and the gas was possibly a product of the chemical reaction. Dr. Wenzel then showed that the gas released was hydrogen by covering up the test tube and leasing the gas towards fire, causing a popping noise.
e. When baking power (NAHCO3) is combined with 6MHCl, a chemical reaction occurs. There were bubbles, suggesting there was a formation of gas. Also, the temperature of the mixture decreased rapidly. This shows that it was a chemical change because the release of gas shows that the reaction is forming a new substance.
2. For each of the following substances used in this experiment, tell whether it is an element, a compound, a homogeneous mixture, or a heterogeneous (crude) mixture:
a. Sulfur is an element, because it is on the periodic table, and periodic table is consist of only elements.
b. Iron is an element, because it is on the periodic table, and periodic table is consist of only elements.
c. Sulfur and iron mixed together is a heterogeneous mixture.
d. Sodium chloride is a compound. First, we can tell from the name of this compound, it consists of two elements; therefore we can conclude that it is a compound of those two elements chemically bonded together.
e. Magnesium is an element, because it is one of the elements on the periodic table.
f. Product of magnesium burned in air is a compound, because when magnesium is burned, it is reacted with existing oxygen in the air. Which means that oxygen atoms are now also included in the product produced, creating magnesium oxide.
g. Sodium hydrogen carbonate is a compound, because its name is consists of three elements, telling us that it is a compound from those three elements. Also, when sodium hydrogen carbonate is reacted with another compound, hydrochloric acid, three different substances are produced. If it was an element, there is no way that there could be so many products produced, if it is reacted with another compound that only includes two elements.
3. Dr. Wenzel first weighted sodium hydroxide and calcium nitrate together in separate test tubes. The weigh was 20.99grams. Then he combined them together, and the two substances performed chemical change. We can tell because the color of both substances changed from transparent to opaque white. Dr. Wenzel then weighted the product and it weighted 20.99grams again. This explains the conservation of mass. Conservation of mass states that no matter how much a matter is changed, the mass stays the same. Taking this experiment as an example, even when the two substances underwent a chemical change, the mass still stays the same. It would be different if gas escaped the solution, however, the mass would still be the same if the escaped gas’ mass is also included.

Discussion and conclusions:
1. Physical properties can be observed without changing the composition of the matter. They can be observed through senses such as smell, touch, see, and heard. Physical properties help identify the nature of a matter. They include the temperature, sound, and physical state. Chemical properties can only be identified through the reaction with other substances. Chemical properties require the change in the composition of the matter. Chemical properties show potential of a matter of performing chemical reaction. Chemical properties include the ability to oxidize, chemical stability, and radioactivity.
2. The most important difference between physical change and chemical change is that physical change can occur without changing the properties of the matter, and the composition of matters change when chemical reactions occur. Other differences include that most physical changes can be easily reversed and chemical change is not. Physical changes are macroscopic rearrangements but chemical changes change the arrangement of atoms. Lastly, few properties of a matter changes after a physical change, but a lot of properties change under a chemical change.
3. * Please see my paragraph for Question 3 of Data Analysis
4. Either a solid or liquid would be easier to measure the mass. One of the reactants was oxygen, in the state of gas, therefore it was hard to measure it’s mass. There also was not a device for keeping track of how much oxygen was used to burn the magnesium. The product of magnesium burned in air is a compound of magnesium and oxygen, therefore if we do not know how much of oxygen was used in this experiment, we cannot calculate the total mass of the reactants.
5. From this lab, I learned what are chemical and physical properties and how to examine a substance and describe the physical properties of each. I realized that chemical properties could only be observed after the experiment is completed, for example, magnesium is flammable. On the other hand, physical properties can be observed prior to the experiment. I also learned how to distinguish chemical and physical reactions. Although I cannot see atoms, I can use other observations, such as bubbles, smoke, color changes, changes in temperature to distinguish chemical reactions from physical reactions. Furthermore, I learned about conservation of mass. It states that the total mass of a matter would always stay the same no matter how many changes it has made. I watched a video on the chemical reaction of thermite and ice. It amazed me on how chemical reactions can be this dangerous and cool!

References: http://www.chemteam.info/Matter/PhysicalChemProperties.html http://chemistry.about.com/od/lecturenotesl3/a/chemphyschanges.htm https://www.youtube.com/watch?v=hw1xhRt9GvU

References: http://www.chemteam.info/Matter/PhysicalChemProperties.html http://chemistry.about.com/od/lecturenotesl3/a/chemphyschanges.htm https://www.youtube.com/watch?v=hw1xhRt9GvU