Solubility Rules

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Solubility Rules Reference Tables
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Components of a Solution

• Solute substance being dissolved
• Ex Salt, Sugar
• Solvent substance doing the dissolving
• Ex Water, Hexane

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• Solubility
• How much solute can
• dissolve under certain
• conditions of
• temp. and pressure.

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Factors Affecting Solubility
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• Surface Area
• More solute/solvent contact
• means faster dissolving
• Crush substance into fine
• powder
• Use mortar and pestle

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• Stirring or Agitation
• More solute/solvent
• contact (solids/liquids)
• However, stirring disturbs
• dissolved gases and they
• come out of solution.

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• Temperature of Solvent
• Higher temperatures will allow more
• solid solutes to dissolve

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• Gases dissolve better when
• solvent temperature is colder.
• Ex CO2 gas in hot soda (flat) vs. cold soda
  (fizzy)

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• Pressure
• Effects gas solubility only
• Why?
• Increasing pressure on
• a gas above a liquid
• causes more gas
• molecules to be
• pushed into solution.
• Ex CO2(aq) in soda

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• Nature of Solute and Solvent
• Polar solutes dissolve in polar solvents
• Nonpolar solutes dissolve in nonpolar solvents
• Most ionics (but not all) dissolve in polar
  solvents (molecule-ion attractions)

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• Amount of Solute already Dissolved
• As particles dissolve in solution fewer
• solvent molecules are available to dissolve
• new solute.

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• Miscible
• 2 liquids that dissolve
• (ex alcohol and water)
• Immiscible
• 2 liquids that do not dissolve (ex oil and
  water)

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• Electrolytes
• Conduct electricity when dissolved in water

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Why do they Conduct?

• Create mobile ions in solution.
• The more concentrated the solution the more it
  conducts
• Includes
• Soluble Ionic Compounds (ex NaCl)
• Acids (ex HCl)
• Bases (ex NaOH)

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Who Will Conduct?

• Which of the following compounds will conduct in
  solution? (ionic salt, acid, base?)
• See Ref Tables for common acids/bases
• C6H12O6
• LiBr
• KOH
• CH4
• H2SO4
• NO2

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• C6H12O6 Will Not (Covalent)
• LiBr Will (Ionic)
• KOH Will (Base)
• CH4 Will Not (Covalent)
• H2SO4 Will (Acid)
• NO2 Will Not (Covalent)

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Using Reference Table G

• Shows solubility in grams of solute per 100 grams
  of water at different temps

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• Saturated Solutions
• hold max solute
• possible at that temp.
• Table G
• Solubility curve lines
• show saturation levels
• at different temps

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• Saturated Solutions are at EQUILIBRIUM.
• Rate of dissolving Rate of crystallization

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• Ex How many grams of NaNO3 are needed to create
  a sat. solution in 100g of water at 50 C?
• Go to 50 C and up to NaNO3 and over.
• Answer 116 grams

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Look at The Water!!

• Table G is for 100 grams of water.
• Amount of water in your problem may be different
  and you need to adjust your answer.

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• How many grams of NaNO3 are needed to
• create a sat. solution in 300g of water at 50 C?
• Answer 116 grams x 3 (three times as much
  water!)
• Or you can use a proportion
• 116 grams x grams
• 100 g H20 300g H20

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• Unsaturated Solutions
• could still hold more
• solute at that temp.
• Would fall below the line
• on Table G
• Ex 40 g of NaNO3 in 100g water at 50

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• Supersaturated Solutions
• hold more solute than they
• should at that temp.
• Would fall above the line
• on Table G
• Ex 140 g of NaNO3 in 100g water at 50

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How do Supersaturated Solutions Form?

• Create a saturated solution at a high temp. and
  slowly let solution cool.
• Certain solutes can stay in solution.
• Ex sodium acetate
• Supersaturated solutions are unstable.
• Add just one more seed crystal, all excess
  solute will precipitate leaving a saturated
  solution behind

Supersaturated Sodium Acetate solution after
seed crystal added
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Describe These Solutions

• Saturated, Unsaturated or Supersaturated?

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• 100 g NH4Cl at 70 in
• 100 g water
• Falls above the line (Supersaturated)

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• 10g SO2 at 10 in 100g
• water
• Falls below the line (Unsaturated)

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• 40g NaCl at 90 in 100g
• water
• Falls on the line (Saturated)

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• Concentrated Solutions
• have a lot of solute
• dissolved in the solvent
• Ex Saturated solution of KI
• at 10
• 135 grams in 100 g water pretty concentrated

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• Dilute Solutions only
• have a little solute
• dissolved.
• Ex Sat. solution of SO2 at 50
• 4 grams in 100 g water relatively dilute

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• If Temp. Changes
• How much will precipitate out of solution if a
  saturated NaNO3 solution at 60 is cooled to 20 ?

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Reference Table F

• Describes which ionic compounds are soluble or
  insoluble in water.
• Certain combinations of ions hold together so
  strongly that water cannot dissolve them into
  solution (insoluble)

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• Is this soluble or not? CaCO3
• Carbonate (CO3-2) is insoluble and Ca2 as a
  partner is not an exception

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• Is this soluble or not? NaNO3
• Nitrate (NO3-1) is always soluble, there are not
  exceptions

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• Is this soluble or not? Li3PO4
• Phosphate (PO4-3) is insoluble, however, Li1 is
  a Group 1 ion so it is an exception and the
  compound is soluble.

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Soluble or Not?

• Look out for exceptions!
• CaSO4
• MgSO4
• PbCrO4
• Li2S
• NH4OH

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• Insoluble CaSO4
• Soluble MgSO4
• Insoluble PbCrO4
• Soluble Li2S
• Soluble NH4OH

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Precipitates

• Precipitates are insoluble ionic compounds formed
  in double replacement reactions.
• Determine which product is the insoluble
  precipitate by using Table F.

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• When a precipitate forms, you create a
  heterogeneous mixture.
• You can separate a precipitate by filtration.
• The solid will stay on the paper.