CHAPTER 16-SOLUTIONS
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Transcript of CHAPTER 16-SOLUTIONS
Solutions
Homogeneous mixtures that may be solid,
liquid or gaseous
• Solute: The part of the solution that is dissolved
• Solvent: The part of the solution that does the dissolving
Water is known as
the universal
solvent
The substance there is the most of is typically
the solvent!
Rate of Solution
• Stirring: Speeds up the rate of solution– Fresh solvent is
continually brought into contact with the surface of the solute
• Temperature: Higher temperature leads to higher rate of solutions– Particles move faster
which brings the solute & solvent together more quickly
• Particle Size: More surface area leads to a faster rate of solution– Powdered sugar dissolves faster than a sugar
cube
Rate of Solution
SOLUBILITY
The amount of solute that dissolvesin a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution
Unit: grams of solute per 100 g of solvent
g solute/100 g solvent
SATURATED SOLUTION• Contains the maximum
amount of solute for a given quantity of solvent at a constant temperature and pressure– If additional solute is added
to a saturated solution, it will not dissolve
– At a state of dynamic equilibrium; the rate of solution equals the rate of dissolution
UNSATURATED SOLUTION
• A solution that contains less solute than a saturated solution at a given temperature and pressure– If additional solute is
added to an unsaturated solution, the solute will dissolve until the solution is saturated.
SUPERSATURATED SOLUTION
A solution that contains more solute than it can theoretically hold at a given temperature• If solute is added to a
supersaturated solution, the crystal will increase in size as more solute precipitates out of solution
• Miscible: Two liquids that will dissolve in each other in all proportions– Any amount of the liquids will dissolve– Example: Ethanol & Water
• Immiscible: Liquids that are insoluble in one another– Example: Oil & Vinegar
FACTORS AFFECTING SOLUBILITY
• Temperature– The solubility of
most solids increases as the temperature of the solvent increases
– The solubility of most gases is greater as the temperature of the solvent decreases
Pressure:• Does not effect
solid or liquid solubility
• Gas solubility increases as the partial pressure of the gas above the solution increases
FACTORS AFFECTING SOLUBILITY
Henry’s Law: At a given temperature, the solubility(S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid
S1 = S2
P1 P2
SOLUBILITY SOLUBILITY CURVESCURVES
Graph that illustrates the
grams of solute that
dissolves in 100 g of water
at a given temperature– The Line: A saturated
solution (# of grams that can dissolve in 100 g water at that temperature)
– Above the line: A supersaturated solution
– Below the line: An unsaturated solution
SOLUBILITY QUESTIONS
1) What happens to the solubility of KNO3 as the temperature increases?
2) 50 g of KNO3 is dissolved in 100 g of water at 30ºC. Is this a saturated, unsaturated or supersaturated solution?
3) 20 g of KNO3 is dissolved in 100 g of water at 60ºC. Is this a saturated, unsaturated or supersaturated solution?
4) How much KNO3 will dissolve at 50ºC?
5) How much KNO3 will crystallize if the temperature is lowered from 40ºC to 10ºC?
6) A saturated solution of KNO3 is prepared in 100 g of water at 30ºC. If the solution is heated to 70ºC, how much more KNO3 must be added to obtain a saturated solution?
1) Which substance shows a decrease in solubility as temperature increases?
2) Which substance exhibits the least change in solubility?
3) Which compound is most soluble at 10ºC?
4) Which compound is least soluble at 50ºC?
5) Assuming no supersaturation, how many grams of K2Cr2O7 crystallizes if a warm solution containing 50 g of K2Cr2O7 in 100 g of water is cooled to 10ºC?
• The concentration is a measure of the amount of solute that is dissolved in a given quantity of solvent– Dilute Solution: One that contains a small
amount of solute– Concentrated Solution: One that contains a
large amount of solute
Molarity (M)The number of moles of solute dissolved in 1 Liter of solution
Molarity (M) = moles of solute liters of solution
Examples: 1) A solution has a volume of 2.0 L and contains 36.0 g of
glucose (C6H12O6). What is the molarity of this solution?
2) How many grams of calcium chloride are needed to make 250 mL of a 2.0 M solution of calcium chloride?
DILUTING A SOLUTION
M1V1 = M2V2 M = Molarity, V = Volume
Examples:1) How many milliliters of aqueous 2.00 M MgSO4 solution must be
diluted with water to prepare 100.0 mL of aqueous 0.400 M MgSO4?
2) How could you prepare 250 mL of 0.20 M NaCl using only a solution of 1.0 M NaCl and water?
PERCENT SOLUTION
Another way to express the concentration of a solution
1) As the ratio of the volume of the solute to the volume of the solution
% by Volume = Volume of Solute x 100%
Volume of Solution
1) As the ratio of the mass of the solute to the mass of the solution
% by Mass = Mass of Solute x 100%
Mass of Solution
PERCENT SOLUTION EXAMPLES
1) What is the percent volume of ethanol (C2H6O, or ethyl alcohol) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water?
2) A bottle of the antiseptic hydrogen peroxide (H2O2) is labeled 3.0% volume. How many mL H2O2 are in a 400.0 mL bottle of this solution?
3) Suppose you want to make 2000 g of solution of glucose in water that has a 2.8% by mass concentration of glucose. How much glucose should you use?