Mixtures and Solutions

1. Mixtures and Solutions Investigation 2 Part 1 Reaching Saturation

2. What is a solution? • How would you test a mixture to find out if it is a solution? • What are some examples of solutions?

3. Inquiry • How can we find out what might happen if you keep adding salt to 50ml of water? • Come up with a plan in your group.

4. Ideas: • Measure 50ml 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.

5. Equipment • Everything you used before (cups, funnel, syringe, salt, water….. • Clear plastic bottle: You can use this to make your solution. The bottle will keep the solution from spilling. You just add the salt, put on the cap, and shake.

6. Funnel • Use the funnel to direct salt into the bottle so none spills.

7. The Challenge • The question you are answering is “how much salt can you dissolve in 50ml of water?” • How much water will you put in the bottle at the start? • How much water will you add later? • Why would you not add any water later?

8. You will need • Your bins • One bottle • One sticky note • Salt supply • 5ml spoon • Balance • A 10g, 5g, and about 6-7 1g weights

9. Procedure • Put 50ml of water (one syringe) into each of the bottles. • 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.

10. Questions: • 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?

11. Saturation • You made a solution by dissolving solid material in a liquid. • In this case, the solution was salt dissolved in water. • When solid material is added to a solution until no more will dissolve, the solution is a saturated solution. You all made saturated solutions. • How do you know you have a saturated salt solution?

12. How much salt dissolved? • We have a saturated solution. How much salt did it take to saturate 50ml of water? • What we really need to know is how many grams of salt does it take to saturate 50ml of water. • In other words, how many grams of salt are dissolved in your saturated solution?

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

14. Procedure • Place a cup under the funnel. • Filter the solution using a wet filter paper. The solution will pass through the filter; the undissolved salt won’t.

15. Procedure (cont): • Place the saturated salt solution on one side of the balance and 50ml of plain water on the other side. • Add gram weights (start with a 10g, then a 5g, then 1g) 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 50ml of water.

16. A salt solution is made of two parts: the water and the salt. These two parts of a solution are called the solvent and the solute. The solvent is the liquid (in this case) into which the solid material goes. The solute is the material that dissolves. A solution is always made of a solvent with some kind of solute dissolved in it.

17. Because so many things dissolve in water, it is sometimes called the universal solvent. Remembering that water is the universal solvent might help you remember that the solvent is the liquid part of the solution into which the solute dissolves.

18. Word Bank: • SolventA substance that dissolves a solute to form a solution.

19. Word Bank: • SoluteA substance that dissolves in a solvent to form a solution.

20. Word Bank: • Saturated solutionA solution in which as much solute as possible has been dissolved.

21. Content/Inquiry • Is there a limit to the amount of salt that will dissolve in water? • Salt will dissolve in water until it reaches saturation. No more salt will dissolve once saturation is reached.

22. Content/Inquiry • How can you determine the amount of salt present in a saturated volume of water? • The amount of salt in a saturated solution can be determined by weighing the saturated solution and subtracting the mass of the water.