Mixtures and Solutions

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Chapter 14

• Mixtures and Solutions

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14.1 Types of Mixtures

• What is a Mixture?
• A combination of 2 or more kinds of matter, each
  retains its own composition and properties.
• Homogeneous a mixture with uniform composition
  (ex salt water).
• Heterogeneous a mixture without uniform
  composition (ex dirty water).

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Types of Mixtures

• Solutions
• A homogeneous mixture in a single phase.
• Properties
• uniform distribution of particles
• wont settle out
• transparent
• cant be filtered out (small particle size)

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Types of Mixtures

• The nature of solutions
• Solute the part that gets dissolved.
• Solvent the part that does the dissolving.
• Aqueous (aq) a solution that contains water as
  the solvent.
• Tinctures solutions that contains alcohol as
  the solvent
• Examples I2 in alcohol, phenolphthalein
  solutions

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Solutions

• Solutions can be electrolytes or
  non-electrolytes.
• What is an electrolyte?
• Salts. Anything that dissolves in water and
  conducts electricity.
• Solutes are classified according to whether they
  dissolve to form neutral molecules or charged
  ions.

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Solutions

• 3 Types of solutions
• Gaseous solutions - air
• Liquid solutions vinegar (acetic acid dissolved
  in water) soft drinks (solutions of a gas, CO2,
  dissolved in water.
• Solid solutions alloys such as sterling silver
  92 silver, 8 copper white gold gold
  containing nickel, tin, zinc or copper.

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Suspensions

• A heterogeneous mixture of the largest particles
  that settle out.
• Example a jar of muddy water, Italian dressing

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Colloids

• Colloids contain intermediate size particles that
  remain in suspension because they are too small
  to settle out.
• Example the large particles settle out of the
  muddy water, but the water remains cloudy. The
  cloudy water cannot be filtered because the
  particles are too small and remain in suspension
  due to the constant movement of the liquid
  molecules.
• Colloids include mayonnaise (solid emulsion),
  foam, smoke (solid dispersed in gas), fog (liquid
  dispersed in gas)

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Colloid or Solutions?
Classify as either a solution or colloid Classify as either a solution or colloid Classify as either a solution or colloid
Rubbing alcohol _______ Rubbing alcohol _______ Milk _______
Medicine _________ Medicine _________ Vinegar _________
H2O2 _______ H2O2 _______ Windex _______
Gasoline _______ Gasoline _______ Mayonnaise _______
Hairspray _______ Hairspray _______ Jello _______
Scope _______ Scope _______ 7-up _______________
Toothpaste _______
C
S
S
S
C
S
C
S
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Classification of Matter
Fill in the flow chart with the following words
Mixtures, Matter, Pure Substances, Homogeneous,
Heterogeneous, elements, compounds, suspensions,
colloids, solutions
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14.2 The solution process

• Factors affecting the rate of dissolving
• Degree of Solubility the amount of substance
  required to form a saturated solution in a
  certain amount of solvent at a certain
  temperature.
• solute solvent ? solution
• (equilibrium)

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Factors affecting the rate of dissolving

• If you wish to dissolve a substance, you can help
  by
• crush it (increase surface area)
• stir it
• heat it

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Factors affecting solubility

• 1. Types of solvents and solutes Like dissolves
  like
• Polar/ionic vs. nonpolar
• water oil
• salt gasoline
• sugar Styrofoam

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Like dissolves Like

• Ionic substances dissolve in polar substances
  salt dissolves in water
• Non polar substances dissolve in non polar
  substances fats, oils, gasoline dissolve
• Immiscible substances do not dissolve in each
  other (salad dressing oil and vinegar)
• Miscible substances do dissolve in each other
  (gasoline and benzene)

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Factors affecting solubility

• 2. Pressure (gases only)
• As pressure increase, solubility increases.
• Henrys law solubility is proportional to
  pressure.
• Effervescence the escape of a gas from a
  solution (a carbonated soft drink effervesces
  when the bottle is opened and the pressure is
  reduced)

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Factors affecting solubility

• 3. Temperature
• For most solids, solubility increases as
  temperature increases
• For gases, solubility decreases as temperature
  increases

S
T
S
T
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Heats of Solution

• Solubility, the nature of solute and solvent, and
  the energy changes during solution formation
• Dissolving an ionic compound in water

Na
Na
Cl
O-2
O-2
Na
Cl
Na
H
H
H
H
Cl
O-2
O-2
Cl-
Na
Cl-
Na
Cl
H
H
H
H
Cl-
Cl-
Step 1 Step 2
Step 3 Breakup the Breakup the
Formation of Formation of the
solvent the
solution Solute (endothermic)
(endothermic) (exothermic)
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Heats of Solution

• If step 1 plus step 2 are more than step 3,
  then the overall reaction is endothermic.
• Energy Level Diagram

E
3
2
1
Time
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Heats of Solution

• If step 1 plus step 2 are less than step 3,
  then the overall reaction is exothermic.
• Energy Level Diagram

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Heat of Solution/Hydration

• Heat of Solution The amount of heat absorbed or
  released when a solute dissolves in a solvent.
• Heat of Hydration energy released when ions are
  surrounded by water molecules.
• The of water molecules used depends on the size
  and charge of the ion.
• ? Heat released (more negative) as the size of
  the ion ?
• Li1 -523 kJ/mole vs Na1 -418 kJ/mole
• ? Heat released (more negative) as the charge of
  the ion ?
• Na1 -418 kJ/mole vs Mg2 -1949 kJ/mole
• Li and Mg are close to the same size, so...
  charge means more

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Heat of Solution/Hydration

• Dissociation - separation of ions caused by the
  action of the solvent.
• Hydration - the process of solute particles being
  surrounded by water.
• Remember polar/ionic dissolves polar/ionic
  (like dissolves like). O2 and CO2 are nonpolar.
  They dont dissolve very much in water (just
  enough for sodas)

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Solubility Curves and Tables

• Solubility Rules
• soluble (definition) more than 1 g of solute
  dissolves per 100 g of water
• slightly soluble between 0.1 and 1 g dissolves
• insoluble less than 0.1 g dissolves
• d decomposes
• ni - not isolated - not been found to form

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Saturated, unsaturated, and supersaturated
solutions

• Saturated Solution
• Holds as much solute as it can at a given
  temperature and certain amount of solvent.
• Temperature must be stated when determining
  solubility.
• For gases, pressure must also be stated when
  determining solubility.

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Saturated, unsaturated, and supersaturated
solutions

• Unsaturated Solution
• The solution is currently dissolving less than
  the maximum amount of solute at a given
  temperature.
• Supersaturated Solution
• The solution currently holds more than the
  maximum amount of solute at a given temperature.
• How is this possible? These solutions are
  created by saturating a hot solution and allowing
  it to cool undisturbed.

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Solubility Problems

• Ex1 What is the solubility of potassium chlorate
  at 50.0 oC in 100.0 ml of water?
• Ex2 What temperature will result in a saturated
  solution of 80.0 grams of sodium nitrate and
  100.0 grams of water?

20.0 g of potassium chlorate in 100.0 grams of
water
10.0 oC
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Solubility Problems

• Ex3 If 40.0 grams of ammonium chloride are
  placed in 100.0 grams of water at 50.0 oC, is the
  solution saturated or unsaturated? If saturated,
  how much salt remains undissolved? If
  unsaturated, how much more salt can be dissolved?
• Ex4 If 80.0 grams of potassium nitrate are
  placed in 100.0 grams of water at 44.0C, is the
  solution saturated or unsaturated? If saturated,
  how much salt remains undissolved? If
  unsaturated, how much more salt can be dissolved?

The solution is unsaturated and can hold 10.0
more grams of ammonium chloride.
The solution is saturated with 5.0 grams of
potassium nitrate undissolved
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Solubility Problems

• Ex5 What is the solubility of sodium chloride
  at 90.0 oC in 50.0 ml of water?
• At this temperature the 100.0 ml of water can
  hold 40.0 grams of this salt. So, if half as
  much water is present, half as much salt will
  dissolve.

40.0 g x 100.0 ml
50.0 ml
x 20.0 grams of sodium in 50.0 grams of water
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Solubility Problems

• Ex6 What is the solubility of potassium nitrate
  at 50.0 oC in 200.0 ml of water?
• 80.0 g x
  100.0 ml 200.0 ml
• x 160.0 grams of potassium nitrate in 200.0
  grams of water

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Solubility Problems

• Ex7 What is the solubility of ammonium chloride
  at 90.0 oC in 68.2 ml of water?
• 70.0 g x
  100.0 ml 68.2 ml
• x 47.7 grams of ammonium chloride in 68.2 grams
  of water

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14.3 Concentrations of solutions

• Dilute vs. Concentrated
• Dilute a small amount of solute in a large
  amount of solvent.
• Concentrated a large amount of solute in a
  small amount of solvent.
• Do not confuse with saturated and
  unsaturated. For example, a saturated solution
  may be either dilute or concentrated.

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by Mass of a Solute in Solution

• Example Suppose we have a solution that
  contains 50.0 ml of alcohol (solute) and 50.0 ml
  of water (solvent). If the density of the alcohol
  is 0.800 g/mL, calculate the following percent
  solutions.
• General Formula ?
• solute 100 by mass
• solution

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Three ways to calculate the solution

• 1 Volume of solute x 100 ?
  Total Volume of solution
• (50.0 ml / 100.0 ml) x 100 50.0

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Three ways to calculate the solution

• 2 Weight of solute x 100 ?
• Total Volume of solution
• D M/ V ? M DV ?
• M (.800 g/ml)(50.0 ml) ?
• M 40.0 g solute
• (40.0 g / 100.0 ml) 100 40.0

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Three ways to calculate the solution

• 3 Weight of solute x 100
• Weight of solution
• D M/V ? M DV ?
• M (.800 g/ml)(50.0 ml) ?
• M 40.0 g solute
• D M/V ?
• M DV ? M (1.00 g/ml)(50.0 ml) ?
• M 50.0 g solvent
• (40.0 g / 90.0g) 100 44.0

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Molarity

• A method used to calculate concentration.
• Molarity (M) moles solute
• Liters of solution
• Note If given grams, use the periodic table to
  find the number of moles
• When you talk about a solution with a label of 6
  M HCl, we say, Six molar solution.

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Molarity

• What is the Molarity of a solution made by
  dissolving 20.0 g of H2SO4 to a volume of 400.0
  ml?

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Molality

• Another method used to calculate concentration.
• molality (m) moles solute
• kg of solvent
• When you talk about a solution with a label of 6
  m HCl, we say, Six molal solution.

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Molality

• What is the molality of a solution made by
  dissolving 3.5 g of Ca(OH)2 in 350 g of water?

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Dilutions

• CoVo CnVn
• Ex. How many mL of water would you need to add to
  6.0 M H2SO4 so you could make 2.00 L of a 2.50 M
  solution?