Mixtures & Solutions
Investigation 3
Part 2
Salt Concentration
Students make two solutions of salt and water and use mass to determine their relative concentrations.
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.
- The more material (solute) dissolved in a liquid (solvent), the more concentrated the solution.
- When equal volumes of two solutions made from the same ingredients, but in different proportions, are compared, the heavier one is more concentrated.
3. Lesson set up and Management
Materials:
If you did not make a packet as mentioned in the FAQ section, copy and give the instructions for salt concentration, Handout #12, and the response sheet for concentration, Handout #13.
Each group needs 3-4 cups. If you have a water station with open pitchers or measuring cups of water, students can just use syringes and get water directly from the station. Students find this easier then trying to get the water from the smaller cups.
Have 8 cups, with two 25ml spoonfuls of kosher salt in each cup, at a chemical station.
If you do not have a sink in the room, have a pitcher for waste liquid disposal.
Each group will need their balance. Remind them to balance their scales using empty plastic cups.
Student Management:
Review the last section's results by having the students share the properties of a concentrated solution.
Remind students they can't use taste as one of the tests in this experiment.
Use the questions provided in the lesson to guide students thinking, and help them connect the soft drink investigation to this experiment.
It is very important that students understand that they must use equal volumes of the solution to get comparable amounts. Ask them why, and have a brief discussion to assess their understanding.
After students have finished, write the solutions as ratios on the board to demonstrate that the heavier solution is more concentrated as a proportion of solute to solvent.
Reinforce the concept of variables in this lesson.
Writing Support:
Have the students do the response sheet, Handout #13, either in class or as homework. Use the scoring guide provided in the teacher's manual to grade these sheets.
Reading Support:
If you have not read “Grow Your Own Crystals”, this would be another time to use this story and connect concentration and saturation.