Description:

In this task, the student is asked to test some factors that might affect the rate at which sugar will dissolve in water. Two studies are to be performed. One is to test the effect of temperature on the rate of solvation and the other is to test a factor which the students come up with themselves.

In question 1, the students record their data, observations, and procedures for the experiments. In question 2, they are asked to explain why these factors affect the rate of solvation.

Students work in groups while performing the experiments and collecting data. Each member of the group must record the data in his or her own booklet. Students work alone while responding to the questions.

This task is designed to take students approximately 45 minutes to complete.

Task Background:

1. There are several factors that effect the rate of solvation. These include: temperature, concentration, surface area of solute, concentration of solvent, and stirring.
   
   
2. The general reason for an increase in rate of solvation is that solute molecules come into contact with solvent molecules more often. To do this, you can increase the # of solvent molecules, increase average speed of the molecules, increase the # of solute molecules exposed to solvent molecules, keep solution at a homogeneous concentration and eliminate foreign molecules.
   
   
3. In order to arrive at a decision from an experiment, there needs to be a control. Only one variable may change at a time.

Overall Task Content Area:

Specific Knowledge Areas:

Performance Expectations:

• conducting investigations
• using equipment
• gathering, organizing, and representing data
• formulating conclusions from investigational data
• applying scientific principles to develop explanations and solve new problems
  

National Science Education Standards:

12 B PS 3: Chemical reactions: Grades 9-12
3.4 Chemical reactions can take place in time periods ranging from the few femtoseconds (10 —15 seconds) required for an atom to move a fraction of a chemical bond distance to geologic time scales of billions of years. Reaction rates depend on how often the reacting atoms and molecules encounter one another, on the temperature, and on the properties — including shape — of the reacting species.

12 A SI 1: Abilities necessary to do scientific inquiry: Grades 9-12

1.4 Formulate and revise scientific explanations and models using logic and evidence. Student inquiries should culminate in formulating an explanation or model. Models should be physical, conceptual, and mathematical. In the process of answering the questions, the students should engage in discussions and arguments that result in the revision of their explanations. These discussions should be based on scientific knowledge, the use of logic, and evidence from their investigation.

(Use the "hot" link on the PALS home page to check the full text of related National Science Education Standards, if desired.)

General Teacher Instructions:

• Students need to be ready to work as soon as the period begins.
  
  
• Group assignments should be made in advance.
  
  
• The materials should be set out at each lab station, if possible.
  
  
• A central supply area, if needed, should be easily accessible.
  
  
• The supply area should have any supplies from the kit that were prepared by the teacher as well as all of the school-supplied materials necessary for the experiment.
  
  
• All the supplies should be clearly labeled.

Materials:

• sugar cubes
• 25 3 oz cups
• 5 Celsius thermometers
• 25 stirring rods
• 5 250 mL measuring cups
• Bunsen burners, alcohol burners, or hot plates
• paper towels
• safety goggles
• ice
• container to hold ice
• beaker tongs or hot pads
• clock
• tap water
• pyrex beakers

Special Directions for Teacher Set-up:

Each group will need 5 cups, 5 stirring rods, one thermometer, and one 250 mL measuring cup. Please have ice (preferably crushed) available for your students to use. You may want to ask them to bring their watches to class the day of the exercise. Using safety goggles is good safety precaution. Groups can share the burners or hot plates. Students should use the beakers to heat water.

Safety:

• Be careful.
• Teachers and students should always exercise appropriate safety precautions and utilize appropriate laboratory safety procedures and equipment when working on science performance tasks.