LAB 5.1: MAKING A SOLUTION
BACKGROUND:
Kool-aid is a solution. In order to make kool-aid, a child mixes the package of kool-aid powder with one cup of sugar and a liter of water. A solution is formed when two substances are mixed to make a homogenous mixture. Homogenous means that the mixture is the same throughout. If you took a sample from the top, bottom, or middle of the solution, each of the samples would be the same. The solid substance that is dissolved is called the solute. The liquid substance the solute is dissolved into is called the solvent. In this lab, you will make a solution that is very much like kool-aid, a sugar solution.
Sugar is a compound that is made up of molecules. A molecule is a neutral group of atoms that acts as a single particle. Each sugar molecule has the formula C12H22O11. The 45 atoms of carbon, hydrogen, and oxygen that compose a sugar molecule are all held by bonds keeping them together as one larger particle. As you prepare the solution in today’s lab, you will need to visualize what is happening to the sugar and water molecules as the sugar dissolves. The particle models (mental images) you’ve already built will be utilized to explain a new process.
PURPOSE: To visualize solutions and the dissolving process in order to develop a model of molecules in solution.
PRE-LAB QUESTIONS:
1. What is a molecule?
2. Which is larger, a sugar molecule or a water molecule? Explain your thinking.
3. Read the procedures and refer to definitions given in the background:
a) In the solution prepared for this lab, what is the solute?
b) What is the solvent of the solution for this lab?
4. a) Draw a particle model of sugar molecules in a solid sugar cube. Note: you can draw each sugar molecule (particle) as a circle like we did last semester. You do not have to show the different types of atoms.
b) Describe the attractions between the molecules. Hint: strong or weak?
5. Read the procedures: The “Mass of all components” will be measured in the lab procedures. List all the components that will be included in the mass measurement.
PROCEDURES:
A. Copy the following table:
Data Table: Mass and Volume of a Solution
Mass of all components (g)
/ Volume of Water (mL) / Volume of sugar(cm3) / Combined Volume
(water + sugar)
Before Dissolving
After Dissolving
*Notes:
- 1 mL = 1 cm3, so you can use either unit in the last column.
- The shaded areas of the table (row 2) are shaded to indicate that no measurements are to be recorded in these areas.
B. Put 50 mL of water in a graduated cylinder. Record the volume of water in the table. Place a rubber stopper on the graduated cylinder.
C.Place the graduated cylinder (with water and stopper) on the metal pan of the balance and place three sugar cubes along side the cylinder . Do not add the sugar cubes to the water yet! Record the combined mass of the three sugar cubes, water, stopper, and graduated cylinder before dissolving in your data table.
D.Find the volume of the stack of three sugar cubes. (Remember: volume = L x W x H, measuring 3 sides from one corner.) Calculate the volume of the sugar cubes and record the value in the table.
E. Calculate the combined volume of the water plus sugar cubes before they are dissolved. (Remember: one ml is equivalent to one cm3, so you can just add the two numbers.) Record the combined volume before dissolving in your data table.
F.Predict what the total volume and mass will be when the three sugar cubes are combined and dissolved in the 50 mL of water. Write a sentence to record your prediction.
G.Carefully slide oneof the sugar cubes into the cylinder. Replace the stopper and gently shake the cylinder until all the sugar has dissolved. Be careful to not spill any water!
H. Continue to carefully add sugar cubes, one at a time.
- Write a sentence to record your observations of the dissolving sugar.
- Write another sentence to compare the rate (speed) of dissolving as you add more sugar cubes.
I. Measure and record the combined mass of the cylinder, water, stopper and dissolved sugar after dissolving all three sugar cubes in your data table.
J. Measure (read the side of the graduated cylinder) and record the volume of the sugar water solution after dissolving in your data table.
INTERPRETATIONS:
1.a. How does the mass of all the components before dissolving compare to the mass after dissolving?
b. Does the mass data suggest that the number of sugar and water particles present before dissolving is greater than, equal to, or less than the number of particles after dissolving?
2. a. After the sugar cubes have completely dissolved, can the sugar be seen in the water?
b. What evidence do you have to support that the sugar molecules are still there?
3. a. Copy and complete the following sentence. Before dissolving, a sugar molecule in the middle of the cube is surrounded by ______molecules.
b. Copy and complete the following sentence. After dissolving, a sugar molecule is surrounded by ______molecules.
c. Visualize the dissolving process, from the solid sugar cube to the sugar dissolved completely in water. What happened to the sugar molecules? Are the sugar molecules still attracted to the other sugar molecules?
4. a. In the sugar water solution, do you think there are more sugar molecules or more water molecules?
b. Draw the sugar solution at the particle level. Show the water molecules (draw as circles; label one as H2O) and the sugar molecules (draw as circles; label one as C12H22O11). Show at least three sugar molecules in your diagram.
c. Think about your particle model of a liquid from last semester and today’s volume data. Are there large spaces between water molecules? Explain your thinking.
5. The Dissolving Process: In order to dissolve, the particles of one substance must end up evenly distributed between the particles of the other substance. Particles must be in motion and colliding to move between each other. To separate the sugar molecules during dissolving, the water molecules must do “work” on the sugar particles.
a. What type of energy do water molecules have? Hint: are the particles moving? KE or PE?
b. What happens to the energy of a particle when it collides with another particle? Hint: think of a car collision.
c. Visualize collisions between water molecules and sugar molecules in the sugar cube. Explain how collisions cause the sugar to dissolve. Hint: think about the change in attractions.
d. Explain why the procedures directed you to shake or stir the mixture to make a solution.
6. a. Use temperature (average K.E.) to explain why sugar will dissolve faster in warm water than cold water.
b. Explain why granulated (loose) sugar dissolves faster than sugar cubes.
7. When you drink kool-aid, what observation suggests that the individual sugar molecules remain intact (as C12H22O11 molecules) rather than dissolving into individual atoms of carbon, hydrogen, and oxygen? Hint: a molecule has different properties than the elements it’s made up of.
8. Table salt (NaCl) also dissolves in water. Draw a particle model of a salt water solution. Label the particles.
CONCLUSION:
- Draw a 2-picture sequence. In the first picture, draw sugar and water molecules at the very beginning of dissolving. In the 2nd picture, draw the sugar mostly dissolved in the water.
- Write a paragraph to describe what happens when a solid substance dissolves. Include details about particle attractions and energy transfer.