Assignment: Introduction to Chemistry Survey

LAB: Concentration Rainbow

Introduction

The quantity of a solute dissolved in a solution is describes in mathematical terms by the solution's CONCENTRATION. This experiment uses colored sugar solutions made at different concentrations.

For this experiment the following materials are needed: (see TIPS below)

• Sugar • Water • Food Coloring
• Tablespoon • 5 Glasses

Experimental Procedure

Safety Issues When Doing the Experiment

It is probably not a good idea to drink your rainbow once you have completed the experiment; no one needs that much sugar in his or her system.

Materials Needed

• Sugar
• Water
• food coloring, five colors
• Tablespoon
• 5 Glasses

Procedure

1. Line up five glasses. Add 1 tablespoon (15 g) of sugar to the first glass, 2 tablespoons (30 g) of sugar to the second glass, 3 tablespoons of sugar (45 g) to the third glass, and 4 tablespoons of sugar (60 g) to the fourth glass. The fifth glass remains empty.

2. Add 3 tablespoons (45 ml) of water to each of the first 4 glasses. Stir each solution. If the sugar does not dissolve in any of the four glasses, then add one more tablespoon (15 ml) of water to each of the four glasses.

3. Add 2-3 drops of red food coloring to the first glass, yellow food coloring to the second glass, green food coloring to the third glass, and blue food coloring to the fourth glass. Stir each solution.

4. Now let's make a rainbow using the different density solutions. Fill the last glass about one-fourth full of the blue sugar solution.

5. Carefully layer some green sugar solution above the blue liquid. Do this by putting a spoon in the glass, just above the blue layer, and pouring the green solution slowly over the back of the spoon. If you do this right, you won't disturb the blue solution much at all. Add green solution until the glass is about half full.

6. Now layer the yellow solution above the green liquid, using the back of the spoon. Fill the glass to three-quarters full.

7. Finally, layer the red solution above the yellow liquid. Fill the glass the rest of the way.

Tips:

• The sugar solutions are miscible, or mixable, so the colors will bleed into each other and eventually mix.

• Try to avoid using gel food colorings

• Artificial sugar will not produce good results

• Wine glasses or actual glass cups work best as opposed to clear plastic

• If your sugar won't dissolve, an alternative to adding more water is to microwave the solutions for about 30 seconds or use warm water in the first place. If you heat the water, use care to avoid burns.

• If you want to make layers you can drink, try substituting unsweetened soft drink mix for the food coloring, or four flavors of sweetened mix for the sugar plus coloring.

Experiment: Rainbow

Questions - circle the best answer.

1. Which of the following is an expression of concentration?

a) 15 g b) 45 mL c) 0.33 g/mL d) 3.0 mL/g

2. Which of the following correctly describes a formula for concentration?

a) (g solute) x (mL solvent) b) (g solute) / (mL solvent) c) (mL solvent) /(g solute)

3. Which of your solutions is the most dense?

a) Red b) Yellow c) Blue d) Green

4. Which of your solutions is the least dense?

b) Red b) Yellow c) Blue d) Green

5. Calculate the concentration of the green solution in grams/milliliters (g/mL). Use 1 Tbs sugar = 15 g sugar and 1 Tbs water = 15 mL.

6. Once you have layered the solutions, stir them vigorously. Wait several minutes. The solution them reforms the layers of various colors.

a) True b) False

7. If you combined oil and water in the same vessel, they separate and form layers.

a) True b) False

8. If you combined oil and water in the same vessel, stirred them vigorously and waited several minutes, they will not separate into layers.

a) True b) False

9. Summarize and explain what you observed when you stirred your sugar solutions.

10. Explain what you observe when you stir the oil and water. Which liquid is the most dense?