Solutions

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Solutions
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Mixtures

• A substance made up of 2 or more elements or
  compounds that are not chemically combined and
  can be separated
• 2 classifications
• 1. Homogeneous--gt mixtures that are spread out
  evenly
• Ex. solutions
• 2. Heterogeneous--gt mixtures are not spread
  out evenly
• Ex. Colloids and suspensions

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KoolAid Salt Water are examples of Homogeneous
Mixtures
Rice Krispy Bars, Paint Pizza are examples of
Heterogeneous Mixtures
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What is a solution?

• A homogeneous mixture
• Ex. saltwater
• Made of 2 parts
• 1. Solute--gt the substance that is considered
  to be dissolved (salt)
• 2. Solvent--gt the substance in which the
  solute is dissolved (H2O)

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How can you tell which is the solute and solvent?

• If 2 substances in the solution were in different
  phases, the one that changed phase is the solute
  (salt), and the substance that did not change
  phase is the solvent (H2O)
• If 2 substances are in the same phase originally,
  the substance in smaller amount is usually the
  solute (40 g alcohol), and the substance is
  greater quantity is usually the solvent (60 g
  H2O)

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Which is the solute and solvent?

• 75 Cu and 25 Zn brass alloy
• CO2(g) and H2O(l)
• carbonated beverage
• O2(g) and air

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Properties of Solutions

• Very small particle size .01 nm-1 nm
• Do not separate upon standing
• Are transparent
• Cannot be separated by filtration
• Particles do not display the Tyndall Effect the
  particles are too small to scatter light

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Examples of Solutions

• Sucrose in H2O
• Food coloring in H2O
• Sodium Borate in H2O
• Carbonated Beverages
• Alloys (2 or more metals)
• H2O vapor in air

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Colloids

• A heterogeneous mixture
• May or may not be transparent
• Medium particle size 1 nm -1000 nm
• Do not separate upon standing
• Cannot be separated by filtration
• Particles display the Tyndall Effect the
  particles are large enough to scatter light

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Examples of Colloids

• Gelatin in H2O
• Milk
• Clouds

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Suspensions

• A heterogeneous mixture
• Are not transparent
• Large particle size over 1000 nm
• Particles settle out
• Can be separated by filtration
• May or may not display the Tyndall Effect

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Examples of Suspensions

• Clay in H2O
• Cooking oil in H2O
• Spoiled milk

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More about Solutions

• Solutions in which H2O is the solvent are called
  aqueous
• If H2O cannot act as the solvent, another liquid
  will
• Ex. CCl4 C6H6 will act as fat solvents in the
  body
• Solutions in which alcohol is the solvent are
  called tinctures
• Ex Betadine solution (I2 crystals dissolved in
  CH3OH)

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• When 2 liquids dissolve in one another, they are
  said to be miscible
• When 2 liquids do not dissolve in one another,
  they are said to be immiscible
• Make sure to use these terms when describing the
  solubility of liquids in one another!!!
• Ex. Ethanol is miscible in H2O
• Ex. Oil is immiscible in H2O

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• Alloys are solutions made up of 2 or more metals
• Ex. Brass 70Cu and 30 Zn
• Ex. Sterling silver (Cu Silver)
• Ex. Amalgam--gt an alloy made Hg and other
  metals that is used to make dental fillings

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Why can we make so many aqueous solutions?

• H2O is known as the universal solvent because
  it can dissolve or be miscible with most polar
  substances
• Remember the Like dissolves like rule
• Polar substances have an unequal distribution of
  electron charge because of certain elements
  stronger or weaker desires to become a noble gas
  within the compound
• Ex. NaCl, C12H22O11, ethanol (C2H5OH)
• Nonpolar substances have equal distribution of
  electron charge because all elements within the
  compound have the same desire to become a noble
  gas
• Ex. Kerosene (CxHy), oil, ethane (C2H6)

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What makes something an electrolyte?

• An electrolyte is a substance that dissolves in
  H2O that conducts an electric current
• A substance must have ions ( and - charged
  particles) to be an electrolyte
• Electrolytes may be classified as strong or
  weak depending on how many ions they produce in
  solution
• Examples include sodium chloride (NaCl),
  potassium phosphate (K3PO4)

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• A nonelectrolyte is a substance that dissolves in
  H2O that does not conduct an electric current
• Nonelectrolytes are polar or nonpolar covalent
  compounds.
• Examples include sucrose C12H22O11 (polar),
  pure water H2O (polar), and iodine I2 (nonpolar)

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How can we increase the rate of dissolution?

• Rate of Dissolution--gt the measure of how fast a
  substance dissolves
• Increase surface area of solute
• Increase the temperature
• Agitate the solution (stir)
• Increase the concentration of solvent so more
  particles come in contact with the solute

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What is solubility?

• Solubility is the maximum amount of solute that
  can dissolve in a certain amount of solvent
• What main factors affect solubility?
• 1. Temperature
• 2. Pressure
• 3. Nature of the solute (polar vs. nonpolar)

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Temperature as a factor

• As you increase the temperature of a solid or
  liquid, solubility increases
• By increasing the kinetic energy, the solvent
  particles are forced to come in contact with the
  solute particles more often and can take on more
  as a result
• As you increase the temperature of a gas,
  solubility decreases
• By increasing the kinetic energy, the gas
  particles are moving too quickly and leave the
  solution before they have a chance to collide
  with the solute (gases do not want to be put in a
  liquid solution!!!)

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Pressure as a factor

• An increase or decrease in pressure of a solid or
  liquid in solution will have no affect on the
  solubility of that solution
• This is because there is little to no ability
  (or space between particles) to compress or
  expand solid or liquid
• An increase in pressure will increase the
  solubility of a gas
• This is because gas particles can be forced
  closer together (or farther apart) due to the
  large spacing between particles

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What is saturation?

• When a solution has the maximum amount of solute
  dissolved in a certain amount of solvent at a
  given temperature, it is said to be saturated
• Saturated solutions are said to be in equilibrium
• rate of solute dissolving in solvent
• rate of solute crystallizing in solvent

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Solubility Curve
All data points on the line represent a saturated
solution
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Unsaturated versus Saturated Solutions?

• When a solution contains less solute than it
  could at a certain temperature, it is said to be
  unsaturated
• When a solution contains more solute than it
  normally could at a certain temperature, it is
  said to be supersaturated
• This is a dynamic condition that is very
  unstable

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Solubility Curve
All data points above the saturation line
represent a supersaturated solution
All data points below the saturation line
represent an unsaturated solution
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Solubility Curve for Gases

• Gases have too much kinetic energy and do not
  want to be dissolved in a liquid
• When temperature increases, solubility decreases
  for gases

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More on gases

• Henrys Law--gt the solubility of gases in a
  liquid is directly proportional to the partial
  pressure of that gas on the surface of that
  liquid
• Effervescence--gt the rapid escape of gas from a
  liquid in which it dissolves

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Dilute Versus Concentrated Solutions

• Dilute--gt a low amount of solute is dissolved in
  a solvent
• Concentrated--gt a high amount of solute is
  dissolved in a solvent
• These terms will not tell us whether a solution
  is saturated, unsaturated, or supersaturated
• The concentration of a solution can be found
  using the Molarity (M) and Molality (m) equations

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Molarity

• M moles of solute / L of solution
• Solution solute solvent
• Sample problem How many grams of sodium
  chloride can be dissolved in 150. mL of water to
  make a .85 M solution?

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• What is the molarity of a solution made up of
  150. mL of ethanol (C2H5OH) in 200. mL of water?
  Dethanol .789 g/mL, Dwater 1.00 g/mL

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Molality

• m moles of solute / kg of solvent
• Sample problem How many grams of CCl4 are
  needed to dissolve 28 g of I2 to make a .050 m
  solution?

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• A solution containing 468 g of sucrose
  (C12H22O11) per liter has a density of 1.18 g/mL.
  What is the molality of this solution?

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How to make a dilute solution from a concentrated
solution?
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• M1V1 M2V2
• M molarity
• V volume
• Sample problem How much 12 M HCl do you need to
  make 500. mL of a 3.0 M HCl solution? How much
  water did you add to the concentrated 12 M
  solution?

concentrated
dilute
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• How much water would you need to make .850 L of
  6.8 M sulfuric acid solution for 18 M solution?