Investigation 2

1. Investigation 2 Reaching Saturation

2. OBJECTIVESStudents will: • Investigate the behavior of solid materials in water. • Gain experience with the concept of saturation. • Measure the volume and mass of solids and liquids. • Compare the quantities of two solid materials required to saturate 50 ml of water. • Compare the solubility of materials in water.

3. Part 1: Salt Saturation • QUESTION: How would you test a mixture to find out if it is a solution? • What do you think would happen if we put two spoons of salt in 50 ml of water? • Would it dissolve to make a solution? How about 3 spoons? 5?

4. How can we find out what might happen if you keep adding salt to 50 ml of water? Inquiry Question Come up with a group plan!

5. Plan Time • Measure 50 ml of water into a cup. • Add salt, one spoon at a time. • Stir to see if it dissolves. If it dissolves add another spoon. • Continue, counting spoons as you go, until no more salt will dissolve.

6. Challenge Reminder • Target question: How much salt can you dissolve in 50 ml? • How much water will you put in the bottle at the start? 50 ml • How much water will you add later? NONE • What would you not add any water later?

7. Procedures • Work in pairs. Each group will get two bottles, but only one salt supply, syringe, and funnel. • Put 50 ml of water (one syringe) into each of the bottles. Then return the water and syringe to materials station. • Put a sticky note on the bottle, with the bottom of the note right at the water level. Use a bit of tape to secure the label. • Add salt one spoon at a time. Shake the bottle until the salt dissolves. Then add another spoon of salt.

8. Discussion • What happened to the salt when you put it in the water? • Where is the salt now? • What happened to the level of the liquid? • Why did the level go up?

9. You made a SATURATED SOLUTION! • When a solid material is added to a solution until no more will dissolve, the solution is a saturated solution. • How do you know you have a saturated salt solution?

10. How much salt dissolved? • Specifically, how many grams of salt dissolved in your 50 ml of water? • PLAN with your group!!

11. HINTS • Is the undissolved salt at the bottom of the bottle part of the saturated solution? • What is the mass of 50 ml of water?

12. Plan • Place a labeled cup under the funnel. • Filter the solution using a wet filter paper. The saturated solution will pass through the filter; the undissolved salt won’t. • Place the saturated salt solution on one side of the balance and 50 ml of plain water on the other side. • Add gram weights to the plain water to achieve balance. The amount of mass added to the water is equal to the mass of salt dissolved in the saturated salt solution. • Record the number of grams of salt it takes to saturate 50 ml of water.

13. New Solution Vocabulary • Solvent: the liquid (in this case) into which the solid material goes. • Solute: the material that dissolves • Universal solvent: is often called water since so many substances dissolve in it.