Lesson

Background

This activity reviews stoichiometry and solutions by making different concentrations of a Kool-Aid solution. There are many ways to calculate the concentration of a substance including: molarity (M), parts per million (ppm), percent composition (% comp), and grams per liter (g/L).

In chemistry, concentration is usually measured by the number of moles of substance dissolved in a liter of liquid. This is called molarity and is expressed as mol/L or M (formula: molarity = moles/volume).

Prelab Questions

1. Calculate the molar mass of Kool-Aid. Assume the solute is pure table sugar, called sucrose. Its chemical formula is C₁₂H₂₂O₁₁.
2. What mass of Kool-Aid is needed to make a 1.0-M solution from 100 mL?
   (Hint: 2 step problem – molarity, mole conversion)
3. What mass of Kool-Aid is needed to make a 0.5-M solution from 100 mL?
   (Hint: 2 step problem – molarity, mole conversion)
4. What mass of Kool-Aid is needed to make a 0.2-M solution from 100 mL?
   (Hint: 2 step problem – molarity, mole conversion)

5. A chemist makes two Kool-Aid solutions with varying concentrations. The chemist makes solution A by dissolving 50.0 g of sugar in 400.0 mL of water. She then makes solution B by dissolving 50.0 g of sugar in 200.0 mL of distilled water. What can be said about the solution’s concentrations? (Use at least three of the following terms in your explanation: saturated, dilute, supersaturated, homogeneous, unsaturated, solvent, solute, solution.)

Purpose

Apply your knowledge to calculate grams of Kool-Aid powder required to make 3 different solutions of Kool-Aid (C₁₂H₂₂O₁₁) with the following concentrations: 0.2 M, 0.5 M, and 1.0 M. Determine the concentration (molarity) of properly prepared Kool-Aid through a taste test.

Hypothesis

Make an educated guess: Which of the three solutions will provide the best tasting drink?

Procedure

Part I:

1. Select your taster(s). Taste the Kool-Aid and rank on a scale of 1to 5 (1 = gross and 5 = amazing taste). Create a data table to record the amount of Kool-Aid used (in grams), color, and taste ranking.
2. Mix the Kool-Aid (C₁₂H₂₂O₁₁) exactly following the directions for 1 serving size. Label cup “Control”
   a. Measure 1 cup of water. Convert cups into liters.
   b. Take the mass of 1 tablespoon of Kool-Aid powder in grams.

Part II:

1. Mark the 100-mL mark on a plastic cup by measuring 2.5 cm from the bottom of the cup and drawing a line. (Usually we would use more accurate measuring techniques, but we can’t drink out of lab equipment.) Repeat on all three cups.
2. Measure the mass of the plastic cup = __________ g
3. Create a data table to record the mass of solute (Kool-Aid) used in grams, color, taste ranking (1 to 5), and smell description for each solution concentration (0.2 M, 0.5 M, and 1.0 M).
4. Use each cup to mass out the correct amount of solid Kool-Aid for each solution sample. Use the mass values from the Pre-Lab Calculations.
5. Add water to the cup until you have 0.1 L of solution (fill it up to the line you drew). Stir. Repeat for all 3 solution concentrations.
6. Observe and taste the solutions you have made.
7. Record your observations: (ex. looked like? Taste? Which seems more concentrated, saturated, supersaturated, unsaturated?)

Analysis

(Reminder: 1 g H₂0 = 1 mL; 1 L = 1,000 mL)

1. Was your hypothesis supported by your lab findings/evidence? Explain.
2. If you were working for the Kool-Aid company, which concentration would you recommend to customers? Explain why, using evidence and reasoning to support your claim.
3. If 104 grams of Kool-Aid (C₁₂H₂₂O₁₁) was dissolved in enough water to make 3.60 L of solution, what would be the:

a. Molarity? b. Grams/Liter? C. % mass composition? d. ppm?

4. Bryan loves Kool-Aid. He makes a super-concentrated solution of Kool-Aid by heating water to boiling and then dissolving Kool-Aid until no more would dissolve. After cooling, he notices that there is a bunch of Kool-Aid powder on the bottom of his solution. What happened? Explain your answer.
5. Assume we added citric acid (H₃C₆H₅O₇) and baking soda (NaHCO₃) to the Kool-Aid solution to create a “fizzy drink”. The following is the reaction that would take place:
   citric acid + baking soda → sodium citrate (Na₃C₆H₅O₇) + water + carbon dioxide
   a. Write out the balance equation for the chemical reaction.
   b. What is the molar mass of citric acid H₃C₆H₅O₇?
   c. If you used 10.0 grams of citric acid how many moles of citric acid would you have?
   d. How many moles of carbon dioxide (CO₂) would be produced from 10 grams of citric acid?
   MULTIPLE CHOICE Explain your answer.
6. If you tried to dissolve Kool-Aid in an ice cube, you would have a difficult time. But ice is the same molecule as water, so why is it so difficult to dissolve Kool-Aid in an ice cube?
   a. In ice, the temperature is too low and so the Kool-Aid becomes a solid.
   b. In ice, there is very little random molecular motion because it is a solid.
   c. The Kool-Aid is lemon flavored, and you don’t really want lemon Kool-Aid anyway.
   d. The water molecules have a stronger attraction to the Kool-Aid than the ice molecules.
7. Which of the following increase the rate at which a solute is dissolved by a solvent?
   a. Keeping the solution completely still.
   b. Placing the solution in an ice bath as it forms.
   c. Heating the solvent to its boiling point before adding the solute.
   d. Leaving the solute in chunks rather than breaking it up before dissolving it.
   

Conclusion

Write one paragraph briefly describing what happened in the experiment, what your data tells you about the experiment (restate your results) and what you learned from completing the experiment.