Start by reading the introduction to the lab below. The purpose of this lab is to identify various physical properties of several chemicals, and to distinguish between physical and chemical changes.
In order to complete this lab, you’ll need to download the spreadsheet from the main moodle page, under this lab link. Right-click on the link and save the spreadsheet on your own computer. Be sure to remember where you saved it so you can find it later. Then open the file in Excel or Open Office so you’re ready to input and save your data.
Intro:
Chemistry is the study of matter. It is very common for a chemist to need to describe a bit of matter as thoroughly as possible. In doing so, the chemist would certainly list physical properties. Many physical properties can be observed using our senses: color, crystal shape, and phase at room temperature are some examples. Other physical properties involve quantitative observations and so must be measured; density, specific heat capacity, and boiling point are three examples. A physical change is any change in a substance that does not involve a change in its chemical composition. During a physical change, no new chemical bonds are formed, and so the chemical composition remains the same. Examples of a physical change are boiling, freezing, expanding, and dissolving.
Matter can also be characterized by its chemical properties. The chemical properties of a substance include all the chemical changes possible for that substance. A chemical change is one in which the substance is transformed to a new substance. That is, there is a change in the chemical composition of the substance. During a chemical change, the atoms are pulled apart from one another, rearranged, and put back in a new arrangement. Examples of chemical change are burning, rusting, fermenting and decomposing.
In this experiment, you will first identify and record various physical properties of substances, using qualitative observations, such as changes in color or phase, and quantitative observations, such as boiling points. In the second part, you will look at changes in matter and determine if they are physical and chemical.
Part A: Physical Properties
You can read about physical properties here (https://moodle.kccd.edu/pluginfile.php/474571/question/questiontext/587938/1/849507/chemical_properties_resource.pdf) Above lists several types of physical properties, some that can be observed and some that must be measured. We’ll deal only with the observable properties here.
Gather 7-9 different substances from your home, garage, local grocery or drug store. Here are some possibilities: baking soda, corn starch, table sugar, fructose, salt, borax, Epsom salts, washing soda, white chalk or calcium supplement tablets, Plaster of Paris (can cause burns to skin – handle with gloves), boric acid (roach poison), sand, or any other compounds (not mixtures) you are curious about. These substances don’t have to be solids; liquids can work too. Here are some safety warnings: bleach should not be combined with acids (vinegar is an acid); acetone (some fingernail polish removers are mostly acetone) and isopropyl (rubbing) alcohol are flammable; don’t ingest any chemical that you don’t know for sure is safe for human consumption; avoid inhaling too much of any volatile liquid; do not touch dry ice with bare skin. The substances listed here and below have been tested together; if you choose other substances and have questions about safety, please email me or post to Cyber Cafe.
Gather some liquids like water, vinegar, rubbing alcohol, tincture of iodine, or another solvent you have around the house to try dissolving your solid materials in. Determine the solubility of each solid in at least 2 liquids. To do this, you’ll need to find some containers for doing your solubility checks in. These containers should be ceramic or glass so they won’t enter into the reactions or be damaged by them. I used short wide drinking glasses. Also, think ahead of time what you will do with the results of your tests – dump them down the drain? Throw them in the garbage? It depends on what you’ve chosen to test. Everything I tested could be dumped down the drain, but if I were testing cement for example, I probably wouldn’t have dumped that down my drain.
Now for the observations: Examine each sample. Record your observations in the spreadsheet. Use a magnifying glass to check out what you can about particle size or crystal shape; record these under “Other physical properties observed” along with anything else you notice (is it magnetic? if liquid, are there bubbles in it? does it have an odor? etc.) When you do your solubility checks, put a pea-sized portion of the solid in the container and add about 5 mL (1 teaspoon) of the liquid. Mix by swirling or stirring (with a wooden stir-stick, new for each test, or a utensil, washed between tests). Record whether the solid was soluble (dissolved completely to form a homogeneous mixture), partially soluble (mixture was slightly cloudy), or insoluble (solid was still visible) in each of the liquids.
Part B: Physical and Chemical Changes:
You can read about physical properties here. I’d like to add a few hints about how you can tell the difference between the two types of changes. If there’s a way to return the material to its original condition, then the change was only physical. If you return it to what looks like its original condition but its mass has decreased or increased, the change was chemical. If the process generates or absorbs heat and is not a phase change (phase changes are physical), it’s a chemical change.
Step 1: Inspect a small piece of steel wool. Grasp it with tongs and hold it in the flame of your gas stove or a lit candle. Remove it from the flame and allow the system to cool to room temperature.
Observe and record here any changes in the steel wool.
Is this a physical or chemical change? Why?
Step 2: Heat a small piece of wax (birthday candle, crayon, or chunk of larger candle) in a pan on a stove. Remove it from the heat and allow the wax to cool to room temperature (maybe pour it onto a paper plate or something easy to clean before it cools).
Record your observations here. Is this a physical or chemical change? Why?
Step 3: Mix table salt and table sugar in a container like you used in Part A (again, I used the short, wide drinking glasses).
Add water and record your observations.
Is this a physical or chemical change? Why?
Step 4: Crush a vitamin C tablet between 2 spoons (front to back). Mix with an approximately equal amount of baking soda in a glass or ceramic container.
Add some water and record your observations.
Is this a physical or chemical change? Why?
Step 5: Cut open a disposable diaper (in the absorbent area) and shake out some of the powder that’s between the layers of paper into a glass or ceramic container.
Add some water and record your observations.
Is this a physical or chemical change? Why?