Mixtures & Solutions
Investigation 3
Part 1
Soft Drink Recipes
Students compare different recipes of soft-drink solution and develop concepts about concentration and its relationship to the ratio of solute to solvent.
3. Lesson set up and Management
Physical and Chemical Changes (CH01 1.3.3)
- Know that matter can undergo changes of state such as evaporation, condensation, or freezing and thawing. Grades K, 1, 2, 3, 4, & 5.
- Understand physical and chemical changes at the particle level and know that matter is conserved. Grades 6, 7, & 8.
Planning and Conducting Investigations (IN02 2.1.2)
- Plan and conduct simple investigations, using appropriate tools, measures, and safety rules. Grades K, 1, 2, 3, 4, & 5.
- Plan, conduct, and evaluate scientific investigations, using appropriate equipment, mathematics, and safety procedures. Grades 6, 7, & 8.
Explaining (IN02 2.1.3)
- Use data to construct reasonable explanations. Grades K, 1, 2, 3, 4, & 5.
- Use evidence from scientific investigations to think critically and logically to develop descriptions, explanations, and predictions. Grades 6, 7, & 8.
- Concentration refers to the amount of dissolved solute in a volume of solvent.
- The more solute (solid) dissolved in a volume of liquid, the more concentrated the solution.
- When more solvent (liquid) is added, the solution is more dilute.
3. Lesson set up and Management
Materials:
Be sure to have enough 3oz paper cups, 2 for each student.
Copy Handout # 11 if you did not make a packet.
Soft drink mix. Be sure you know the measurements for the type of drink mix you have. They don't always match the proportions used in the book.
Get one sugar free soft drink mix if you have any diabetics in the class. Mix the soft drink as stated on the container so the student will be able to drink some too (however, they will not be able to compare concentrations).
If you buy pitchers with metric markings, you will not need the 1000L beaker.
Student Management:
The book suggests having students help with the mixing. Even though students may want to help, their measurements are not always accurate. It is better to do this whole investigation as a demonstration and stress the importance of accuracy in measurement.
Be sure to have the students mark their cups 1A and 2B.
Go over the recipe page with the class.
Remind students to observe the solutions before tasting. Tell them to compare the colors in the clear vials; and smell by wafting - waving their hands over their cups towards their noses. Now is a good time to teach students that they should never smell directly over any container, especially in a lab setting!
Remind students to record their observations on Handout #11.
The questions for these investigations on page 11 of the teacher's manual are good. Additionally, you could ask the students how they would know if the solution was saturated.
Do solutions 1 and 2 first, and have the students record all of their observations. Then do A and B, and have the students record their observations again.
This is a great time to talk about manipulated (changed) and controlled variables (kept the same), which are terms used in the WASL. Have the students look at the four different solutions and discuss which was changed (manipulated) in each, the water or the powder, and which stayed the same (controlled). Explain the concept of variables using these examples.
If the students have had ratios and percents, you can use this as a math lesson extension. After the tasting, put the proportions of all four solutions on the board and tell the students that by using math they can tell without tasting which solutions are more concentrated. Put each solution in a fraction ratio, such as 25cc/1000cc or 75cc/1000cc, to do the concentration comparisons. This creates great discussions as you show the students the math or ask them in their groups to do the problems.
Another good discussion is to connect this concept to food students may make at home, like orange juice or soup from concentrate. Make sure to ask if they know how to prepare these items.
Writing Support:
Have the students add the word bank entries into their journals and answer the content/entries question as well. You can also have them check their kitchens and make a list of any concentrated food items they find and what the proportions are for making that food. Start the next class with a discussion of what they find. Also have them write out the definitions for manipulated and controlled variables.
Reading Support:
You can bring in labels from food concentrate and have the students read the directions. Baby formula is an interesting example. Have students find and bring in three different types of baby formula: a can of ready to serve; liquid concentrate; and powdered. After they have done this, you can discuss what would happen if a parent mixed the formula wrong (too concentrated is very harmful, as babies will get ill from a dangerously high salt concentration in their blood streams). This points out the importance of reading and following directions carefully. This actually happened in a remote African village when baby formula concentrate, with English directions, was sent as aid. The formula was liquid concentrate so the mothers, who did not speak or read English, thought it was ready to feed to their children. Tragically, several children died as a result.