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Course, Subject

Chemistry, Math, Science & Technology

Author

Dick Chapleau,
1995 California Teacher of the Year
1995 Milken Foundation National Educator
1996 ACS Western US Regional Outstanding HS Chemistry Teacher

Safety

Although benzoic acid is not a particularly harmful chemical, is does serve as a food preservative and will irritate both eyes and skin if contact occurs. Do not play with the chemical solution. Leave the jar closed.

Lab Report Requirements

There is no write-up for this lab. No "Bah, humbug" lab reports for you to do!

Procedure

1. Obtain a hot plate and 250 ml beaker. Heat about 75 mls of tap water on the hot plate, but do not allow it to boil!! While the water is heating, obtain between 0.9 and 1.1 grams of benzoic acid. Please put the cap back on, because the smell of benzoic acid is pretty bad.
2. Place the benzoic acid into the heated water. Turn up the heat and stir the mixture until the benzoic acid completely dissolves and makes a solution. Remove the solution from the hot plate and allow it to begin cooling.
3. Take your Holiday figure and your VERY DRY AND CLEAN baby food jar over to the hot glue station. Use a pair of forceps to hold the figure by its head with your most coordinated hand. Use your other hand to put some hot glue on the bottom of the figure, and then immediately place the figure on the bottom of the baby food jar. Hold it for a few seconds so it stays in place. Allow the glue to cool for several minutes.
4. Watch your benzoic acid solution as it begins to cool, and you will see beautiful snowy looking crystals appear. Allow the solution to completely cool to room temperature (if you don't, the figure usually falls off).
5. After your solution is cool, and the figure has been glued, stir the snow mixture a few times, then quickly pour it into the baby food jar, on top of your holiday figure. You will not fill the jar with this procedure. Then slowly add tap water to fill the jar to the brim (use the graduated cylinder, don't try doing it directly from the faucet).
6. Place your cap on tightly. If all is well, you should be able to turn the snow scene upside down and watch your figure get buried in the blizzard!!
7. Something you can try when you get home is to use some silicon adhesive around the edge of the jar lid to seal it completely. If your figure ever comes loose, you can repair it by opening the jar, pouring the solution into a disposable cup, re-gluing the figure back on, and then replacing the solution. If you lose a little solution, just add more tap water. BE CAREFUL NOT TO DRINK FROM THAT CUP OR TO GET ANY OF THE SOLUTION IN YOUR EYES! It will drive them nuts.

Description

In this lab, you will learn about how some solutes that are only partly soluble can be forced to fully dissolve with heat. When a solute has dissolved as much as it possibly can, and no more will dissolve no matter how much you stir it, the solution is said to be "saturated." If you take a saturated solution and heat it, the extra solute will dissolve. When you then cool the solution, the extra solute that dissolved with heat will once again precipitate. The lab you are doing today is a beautiful application of that principle of solubility.

Related Academic Standards

New York State

S.HS.PS.2.6 Students who demonstrate understanding can communicate scientific and technical information about why the particulate-level structure is important in the functioning of designed materials.

S.HS.PS.1.5 Students who demonstrate understanding can apply scientific principles and evidence to explain how the rate of a physical or chemical change is affected when conditions are varied.

S.HS.PS.1.11  Plan and conduct an investigation to compare properties and behaviors of acids and bases.

MST4.C.C.PS3.1 Students explain the properties of materials in terms of the arrangement and properties of the atoms that compose them.