Dissolving%20and%20%20Solubility

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Chapter 6.2

• Dissolving and Solubility

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Making process of dissolving FASTER!

• Many of same things that make chemical reactions
  go faster
• But DISSOLVING IS A PHYSICAL CHANGE, NOT A
  CHEMICAL CHANGE.

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Faster dissolving

• When a chunk of something dissolves, you are just
  pulling it apart into smaller bits (even down to
  individual molecules or ions)

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Faster dissolving

• heat
• stirring
• shaking
• smaller chunks (larger surface area)

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In a solution, the solute molecules are randomly
distributed among the solvent molecules
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Figure 15.1 Dissolving of solid sodium chloride.
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• The solute is the substance that dissolves in a
  solution.

• The solvent is the substance that dissolves the
  solute to make a solution.

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Why is water such a great dissolver (solvent) for
other substances?
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Water is polar...

• It has a slightly negative side by the oxygen
  atom, and slightly positive side by the
  hydrogens.

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Water can dissolve ionic compounds, and covalent
compounds that are polar (have slightly
negative and slightly positive parts).
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The interaction of polar water molecules with ions
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Representation of the polar hydrogen chloride
molecule
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Chlorine hogs the electron blanket,
leaving hydrogen partially, but positively,
exposed
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Figure 15.3 The ethanol molecule contains a
polar OH bond.
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Figure 15.3 The polar water molecule interacts
strongly with the polar OH bond in ethanol.
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Soap

• The nonpolar side of a soap molecule is
  attached (attracted to) nonpolar grease and
  oil, the polar side hangs on to the water, and
  the dirt slips off your hands and is pulled down
  the drain, trapped, along with the water
  molecules, by that pesky soap molecule!

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• (a) non-polar gasoline and non-polar oil mix
• polar vinegar and nonpolar oil do not mix
• (c) polar water and polar ethyl alcohol mix

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Figure 15.6 An oil layer floating on water.
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For a more detailed explanation of why polar and
nonpolar materials cant dissolve each other

• http//www.knoxnews.com/kns/science/article/0,1406
  ,KNS_9116_1971484,00.html

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Saturated and Unsaturated

• A saturated solution contains the maximum amount
  of solute that can dissolve.
• Undissolved solute remains.
• An unsaturated solution does not contain all the
  solute that could dissolve

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Supersaturated Solutions
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To see more of this supersaturation experiment

• http//www.csudh.edu/oliver/demos/supersat/supersa
  t.htm

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To see more exciting supersaturation stuff, go to

• Crystallization from Supersaturated Solutions of
  Sodium Acetate

• Note, you may need to hit refresh to get
  demonstration started and restarted.

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Solubility

• The maximum amount of solute that can dissolve
  in a specific amount of solvent usually 100 g.
• g of solute
• 100 g water

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Molarity

• Concentration unit of a solution that expresses
  moles of solute dissolved per liter of solution.
• To make a 1 molar solution of a substance, put 1
  mole of stuff into a container and add solvent
  (usually water) up to the 1 liter mark.

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Not this type of Mole
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Or this type of Mole
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Mole

• 6.02 x 1023 is a mole -602,000,000,000,000,000,000
  
• If you counted paper at the rate of one sheet per
  second it would take you 19,089,294,774,226,281
  years to count a mole of paper.
• It is a big number because atoms are small.

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• A mole of sugar weighs about one half pound but
  contains how many molecules of sugar?
• 602,000,000,000,000,000,000
• 6.02 x 1023 molecules.

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Temperature and Solubility of Solids

• Temperature Solubility (g/100 g H2O)
• KCl(s) NaNO3(s)
• 0 27.6 74
• 20C 34.0 88
• 50C 42.6 114
• 100C 57.6 182
• Does the solubility of solids seem to increase
  or decrease with an increase in the
  temperature?

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• A. Why would a bottle of carbonated drink
  possibly burst (explode) when it is left out in
  the hot sun ?
• B. Why would fish die in water that gets too
  warm?

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Solutions

• A. Gas in the bottle builds up as the gas
  becomes less soluble in water at high
  temperatures, which may cause the bottle to
  explode.
• B. Because O2 gas is less soluble in warm water,
  the fish may not obtain the needed amount of O2
  for their survival.