07 Solubility And dissolving salt Science By the Horns

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07 SolubilityAnddissolving saltScience By the
Horns

• Summer 2006
• To get back to activities page
• http//128.83.243.140/ScienceByHorns/activities.ht
  ml

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Foss Kit Connection

• Explore saturation in FOSS kit where emphasis is
  on conservation of mass
• And/or focus on saturation by
• Measuring 40 ml of water into a container
• Have each group measure in salt in either 1 ml or
  1/4 tsp amounts
• (start with 5 quick ones)
• Add this set amount, replace top, then shake
  until the salt disappears
• Repeat until a few grains of salt remains on the
  bottom of the bottle (make sure youve shaked it
  vigorously)
• The solution is saturated

3
Foss Kit Extension

• Histogram the results with Post-ItTM Notes where
  each group places its results.
• You may want to repeat this experiment Compare
  the results from the two trials
• (You may want to do the Histogram and Likeliness
  Activity before this).
• Discussion questions
• Where is the data centered
• If 2 trials, how alike? Different?
• Where is the salt going?
• If you tasted the water, what would it taste
  like? (This means the salt has not changed.
  Dissolving is a physical process, not a reaction
  where the salt would be changed

4
Shifting Saturation and Making Hot Chocolate

• While discussing results heat the water bottles
  in hot water (hot pot)
• What happened to the salt at the bottom? Where
  did it go?
• Heating makes water more energetic so it can pick
  up more salt.
• Think of examples where this happens at home.
  Have you ever tried to put hot chocolate into
  cold water yech! But when you heat it, what
  happens? More hot chocolate can go into solution.

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What if we cooled it?

• If we now cooled the solution and waited a long
  time, the salt would come out of solution.
• May want to use sodium thiosulfate pentahydrate
  to show what would happen (available from UT).
  Note the temperature as solidifies. (Gives off
  heat as gets more ordered increased entropy as
  heated heat comes out as cooled).