Saturation

Dissolving Does sodium chloride dissolve in water? Yes How do we know? It disappears into the water. It is still there because the sodium chloride returns when a salt solution evaporates.

What happens at the particle level when sodium chloride dissolves? The kinetic energy of moving water particles breaks individual particles off the crystals of salt. The salt particles are attracted to water particles and the salt particles move into the water.

In Part 1 you added a 2-mL spoon of salt to 30 g of water. The salt dissolved. What do you think would happen if you added another 2-mL spoon of salt? Would it dissolve? Is there a limit to the amount of a substance that will dissolve in a measure of water?

If so, is the amount of a substance that will dissolve in a measure of water the same for all substances?

Work with your group Create a plan to answer the three questions. Look at the bottle I have I have a supply of these bottles with caps and these large scoops. You may want to use one or more in your plan.

Discuss a Plan What makes a good plan Put a measured volume (mass) of water in one of the bottles Put in salt. Cap the bottle and shake until all of the salt dissolves. Add more salt by scoops until you have used all the salt or solid salt accumulates on the bottom of the bottle.

Plan Determine how much salt actually dissolved in the water Repeat the procedure with a second solute and compare.

How Much Will Dissolve? LM page 78 Read the questions silently as I read aloud. The questions are posed in a context of 30g (mL) of solvent (water) and two solutes are used table salt and Epsom Salts (NaCl and MgSO 4 ).

Hints Make the solutions in bottles with caps to prevent spilling. Shaking will speed up the dissolving Use self-stick notes to label the two bottles. Stick them to the bottles at the water level for reference later 2 students might take charge of the NaCl and 2 take the MgSO 4 The dry funnel can be used to guide the salts efficiently into the bottle Dry the end of the funnel with a bit of paper towel if it gets even a singe drop of liquid on it

Gather Data General Rule If you are not sure if the solid dissolved add another scoop and shake.

Saturation When you dissolve a solid substance in water until no more will dissolve, the solution is a saturated solution. If you continue to add solid material to a saturated solution, the solid will simply pile up on the bottom of the container.

Saturated Solutions Did sodium chloride and magnesium sulfate dissolve in water? What is your evidence? Less solid material is observable on the bottom of the bottles than was placed in the bottles with the water. The final volume of liquid in the bottles is significantly greater than the starting volume.

Were you able to make a saturated sodium chloride solution? What is your evidence? Yes The solution has un-dissolved sodium chloride on the bottom.

Were you able to make a saturated magnesium sulfate solution? What is your evidence? Yes The solution has un-dissolved magnesium sulfate on the bottom.

Did the amount of liquid in the bottles change? Why? Yes, The volume of the solution increased because the solute dissolved and entered the solvent. The solute occupies space, so the volume of the solute plus solve increased.

Did the amount of water in the bottles change? No No water was added or removed The change in volume was due to added solute, not added water.

Did it take the same amount of sodium chloride and magnesium sulfate to saturate 30g of water? No It took a lot more magnesium sulfate to make a saturated solution.

How many grams of sodium chloride and how many grams of magnesium sulfate are needed to saturate 30g of water?

Find a solution Discuss with your group how to find a better solution to this problem. 5 minutes

30g of water, an unknown mass of substance dissolved in the water, and an unknown mass of substance that is not dissolved. Filter out the un-dissolved material with a coffee filter. The saturated solution passes through the filter. Weigh the saturated mass and subtract from 30g. The difference is the mass of the substance dissolved in the water.

Complete the inquiry Lab Manual “How Much Will Dissolve?” B sheet CLEAN UP

Share results Complete lab manual page 79

What happened when the first scoop of NaCl was added to the bottle of water? The water particles banged into the crystals of salt and broke particles of sodium chloride free. The NaCl particles were attracted to the water particles. The salt particles moved into the volume of water surrounded by water particles

Class work Complete lab page “Deeper Thoughts” section Homework Complete Response Sheet -Solutions LM page 81