CHEMISTRY NOW: Sugar Cube Investigation (Grades 5-8) Print

Objective:

Students will investigate the rate at which sugar cubes dissolve. Students will design and carry out an investigation to determine the fastest way to dissolve a sugar cube. Students will use the scientific method to develop an investigation with a control and independent and dependent variables. Students will be able to calculate the rate at which the sugar cube dissolves. Students will use their experimental data and observations to draw conclusions about which factors affect the rate at which a solute dissolves.


Introduction Notes:

CHEMISTRY NOW: Sugar Cube Investigation

 

Subject Area: Chemistry                                                        

Grade Level:  Middle School Chemistry                                

Lesson Title:  Sugar Cube Investigation

 

National Science Education Standards:                                                  

Science as Inquiry: 5–8                                                          

Properties and Changes of Matter: 5–8                                                            

 

Suggested Prior Knowledge: concepts of matter, atoms, molecules, solubility, solutions, solute, solvents, and rate of reaction

 

Purpose: To understand factors that affect the rate at which a solute dissolves.

Key Vocabulary:  

agitation—stirring

rate of change—speed at which a change takes place; how fast the solute dissolves

solute—substance dissolved in a solution

solution—homogeneous mixture of a solute dissolved in a solvent

solvent—substance that dissolves the solute in a solution

surface area—how much exposed area a solid object has; in this case, how much of the sugar is actually in contact with the solvent

Objectives:      

  1. Students will investigate the rate at which sugar cubes dissolve.
  2. Students will design and carry out an investigation to determine the fastest way to dissolve a sugar cube.
  3. Students will use the scientific method to develop an investigation with a control and independent and dependent variables.
  4. Students will be able to calculate the rate at which the sugar cube dissolves.
  5. Students will use their experimental data and observations to draw conclusions about which factors affect the rate at which a solute dissolves.

Materials:  

- Safety goggles

- Sugar cubes

- Water

- 50 or 100 ml graduated cylinder

- Thermometers

- 50 ml beakers

- 250 ml beakers

- Stopwatch

- Stirring rod

- Hot plate

Procedure:

1. Discuss with students how solutions form, and review the concepts of solute, solvent, solution, and dissolving. Begin with discussion of solutions students see in their everyday lives, such as sodas or hot cocoa (powdered hot cocoa is always a popular and familiar solution). Discuss the difference between melting and dissolving.

 

2. Sugar is a common solute in both hot cocoa and sodas. The dissolving of sugar is a process whereby the sugar molecules break apart into individual molecules, which are surrounded by water molecules. The sugar does not chemically change into another substance; but undergoes a physical change. The sugar molecules are also not liquid molecules. Beginning with observation of a sugar cube dissolving might help students.

 

3. Explain that students will work in cooperative groups to design and carry out an investigation into the rate at which a solute dissolves in water. Their solute is sugar cubes. Guide students as they identify variables involved in rate of dissolving (agitation, temperature, and surface area). Students will work to design a valid investigation that will allow them to measure the rate at which the sugar cube dissolves, and examine the factors that will make it dissolve more quickly. Begin with a leading question, and follow-up:

  • - How does the hot cocoa powder dissolve?
  • - What is in the soda?
  • - What are the solutes in each case?
  • - What is the solvent?
  • - How does a solute dissolve?
  • - How can you tell the sugar cube has dissolved?
  • - What substance is dissolving?
  • - What happens when the sugar dissolves in the water?
  • - What can you do to make the sugar cube dissolve more quickly?

 

4. Work with students to design a valid investigation similar to the one outlined in this lesson plan. Guide them to develop a hypothesis and identify the variables they will test. Work with students to determine what will be their control and what will be the independent and dependent variables in the experiments. Students should be limited to a specific quantity of water (30 ml/trial) and sugar (one cube/trial). This keeps the amounts reasonable and the cost down. Students should determine a list of materials they will need to carry out their investigations and they should develop an appropriate data table.

 

5. Ensure that students outline the steps of their procedure carefully. Some leading questions include the following:

  • - How will you measure the amount of water?
  • - How will you determine that the sugar cube is fully dissolved?
  • - How do we measure the rate of dissolving?
  • - What data will you need to collect?
  • - How will you compare your results?
  • - Can we make some predictions about what will speed up the rate of dissolving?

 

6. Lab safety equipment should be used, and safety protocols followed.

 

7. Students may want to initially determine the average mass of a sugar cube so that they can calculate the rate of reaction in grams/second.

 

8. Some general procedures/variables that could be used:

a. Agitation (stirring)

1. Set up three 50 ml beakers (A, B, C).

2. Place 30 ml of water into each beaker.

3. For each beaker, start timing as soon as the sugar cube is dropped into the beaker. For the control beaker (A), do not stir the solution. For the second beaker (B), stir the solution slowly, about once every 30 seconds. For the third beaker (C), stir the solution rapidly, about once every second.

4. Record the time required for the sugar cube to completely dissolve in each of the three beakers.

 

b. Temperature

1. Set up three beakers (A, B, C).

2. Place 30 ml of room temperature water in beaker A, drop in the sugar cube and begin timing. Record the temperature of the water and how long it takes for the sugar cube to dissolve completely.

3. Repeat step 2 with ice water and then again with hot water.

 

c. Surface area

1. Set up three beakers (A, B, C).

2. Place 30 ml of water into each of the beakers.

3. In beaker A, drop in a sugar cube and begin timing. Record the time it takes for the sugar cube to completely dissolve.

4. In beaker B, repeat step 3 using a sugar cube that has been broken into several pieces.

5. In beaker C, repeat step 3 using a sugar cube that has been crushed into small pieces.

6. Students can also use an identical mass of granulated sugar or even powdered sugar.

 

9. After the students have finished their investigation, they may present their findings to their classmates and compare their results with those of their classmates. Students should create graphs of their results and calculated reaction rates.

 

Additional Resources:

         http://www.flinnsci.com/Sections/Safety/safety.asp

         http://answers.yahoo.com/question/index?qid=20081010002429AAjdMUF

         http://www.sparknotes.com/chemistry/solutions/solubility/section1.html

         http://www.sciencebyjones.com/solubility.htm

         http://en.wikipedia.org/wiki/Surface_area

 

 

 

 

 

 

 

 

Student Worksheet Sugar Cube Investigations

 

 

Experiment Title: _____________________Date: _________Name: __________________

 

Student Hypothesis or Question:

 

_______________________________________________________________________

 

Materials:

 

_______________________________________________________________________

 

_______________________________________________________________________

 

_______________________________________________________________________

 

_______________________________________________________________________

 

_______________________________________________________________________

 

 

Safety Precautions:

 

_______________________________________________________________________

 

_______________________________________________________________________

 

_______________________________________________________________________

 

Procedure:

 

Wear Safety Goggles for all lab work.

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

_______________________________________________________________________

Data and Observations:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Analysis of Data:

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

 

______________________________________________________________________

 

Conclusions: 

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

 

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