Saturation
Dissolving
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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 MgSO4).
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 MgSO4
• 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