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Supersaturated Solutions: Rock Candy Lab 

Purpose: The purpose of this lab is to show the properties of supersaturated solutions using crystal growth.

Intro: In this lab we will visually learn the differences between an unsaturated, saturated, and supersaturated solution by creating rock candy.

Materials: 

250mL beaker

Scale

Sugar

Water

Clean Jar

String

Stirring Rod

Candy

Safety:

Caution hot

Use clean items

Procedures:

1) Put 150mL into 250mL beaker.

2) Measure out 450g Sugar.

3) Put in 1 spoonful of sugar at a time, try to dissolve it in the water. (food coloring may be added)

4) When the solution is saturated, allow water to get hot, but do not boil.

5) Then, get 15cm of string and tie a lifesaver on it. 

6) When solution is hot, stop heating it, add 1 spoonful of sugar at a time until the sugar can't dissolve.

7) Stir to help dissolve sugar. When sugar does not dissolve and some is at the bottom of beaker, it is supersaturated.

8) Tie  string to popsicle stick so it hangs down in the jar but doesn't touch the bottom.

9) Pour cooled solution into jar.

10) Cover jar with foil to keep dirt out. Don't bump liquid. Wait for crystals to form.

Discussion:

1) What is the difference between an unsaturated, saturated, and supersaturated solution?

   A)  Unsaturated, has less dissolved solute than the maximum amount that can be dissolved at given                              pressures and temperatures. Saturated, has all the dissolved solute possible at given conditions of temperature and pressure. Supersaturated, has more dissolved solute than is normally possible at given conditions of temperature and pressure.

2) What was the solute in the lab?    

   A) Sugar, cinnamon, and food coloring 

2b) What was the solvent in the lab?

   A) Water

3) Why is it necessary to heat a solvent in order to make a supersaturated solution?

   A) Heating the solvent is what causes it to absorb more sugar and go from saturated to supersaturated.

4) Describe a point in the lab where each of the following happened.

     a) unsaturated solution: In the very beginning of the lab when we had to pour sugar in without heating the solvent first. 

     b) saturated solution: When we kept pouring sugar in until it all fully dissolved in the water.

     c) Super saturated solution: When the solution was hot and we kept adding and adding sugar until       it refused to dissolve and sank to the bottom.  

5) Why was it necessary to use a "seed candy"?

    A) It was necessary to use a seed candy because it helped the sugar molecules climb up and hold on to something while it formed. 

6) Sugar dissolves easily in water. Since "like dissolves like", what does sugar's solubility in water tell you about the properties of sugar molecules?

   A) This tells us that there are water particles in sugar molecules since the sugar eventually dissolves into the water during a saturated solution.

7) Besides increasing the temperature of the water, describe two ways you could get sugar to dissolve in water faster.

    A) 1) you can stir the solution until it dissolves or 2) if the substance is lumped, you could crush it into a finer power.

8) Try to come up with another method to create a supersaturated solution that does not involve heating.

   A) 

9) 

    a) Calculate the molarity of the solution: 153900moles/

    b) Calculate the molality of the solution:  

Conclusion:

A: I followed the instructions to a T and ended up with a supersaturated solution. I knew that this was a supersaturated solution because most of the sugar had settled on the bottom of my jar and wasn't dissolving anymore. Then I quickly placed a cover over it so dirt wouldn't get in. 

B: The general shape of my crystals was jagged. It seems like all the sugar that I had added to the solvent in the beginning morphed together. I don't think I was very successful with making rock candy, I only formed a little on the stick, most of it just formed inside of the jar. 

C: I had problems with my rock candy growing on the stick itself. All of my crystals decided to form inside of the jar instead of on the candy or on the stick. Next time, I think I can avoid it turning out wrong by covering it faster after I've heated it or seeding my string better.