unit 7: solutions, acids, & bases. i. definitions and types of solutions a. what exactly is a...
TRANSCRIPT
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Unit 7:
Solutions,
Acids, & Bases
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I. Definitions and Types of Solutions
A.What exactly IS a Solution?
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B. Types:
[Vocabulary terms…]1] Unsaturated
2] Saturated
3] Supersaturated
4] Suspensions
5] Colloids
6] Alloys
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Question…
HOW do we create solutions?
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C. Forming Solutions
Polar solvents mix best with __________solutes!
How do IMF’s relate to this concept?
Nonpolar solvents mix best with ________________ solutes!
Examples…
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Like Dissolves Like…
See Table 7.1 on pg. 119 of Review book!
SoluteNonpolar Solvent
Polar Solvent
Nonpolar
Polar
Ionic
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II. Collision Theory
Molecules need the proper orientation and proper amount of kinetic energy to create a solutionRemember the formation of Salt Water
demonstrations? How did the orientation of the water impact
the solvation of the Na+ and Cl- ions?
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Combining the Solute and Solvent
Two major criteria need to be met:1: “Like Dissolves Like” = need
compatible bond types and IMF’s
2: Effective Collisions = For a substance to dissolve into a solvent, there must be an “effective collision” between solute and solvent
Need sufficient KE and proper orientation!
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Factors Affecting the Formation of a Solution
1] TemperatureTemperatureIncrease in Temp = Increase in KE, & increase in # of total collisions
3] PolarityPolaritySimilar bond types and IMF’s form solutions faster
2] Surface AreaSurface AreaIncrease in S.A. means more particles contact the solution, & increases the total # of collisions
4] Pressure (gases only)Pressure (gases only)Increases in Pressure cause decreases in volume, and make gases more soluble
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Other Solutions Terms…
Precipitate out = this refers to the solid precipitate that ‘falls out’ of a solution when an irreversible double replacement reaction occurs; Solid may be collected!
Miscible = substances that completely and evenly mix together at any concentrations
Immiscible = do NOT mix to form a solution
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Forming Solutions
Temperature Changes: Increases = most
solids have higher solubilities
EXCEPTION = gases!
Lower solubility at higher temperatures
Pressure Changes: Increases = most
gases have higher solubilities
Liquids and solids = Exceptions!
Little to no solubility differences with changes in pressure
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III. Collision Theory
Collision theory = scientific description of how solutions are formed
May have several factors that help collisions occur faster
Need _____________ collisions with particles that have sufficient __________ for a solution to occur!
Do you have any ideas on how to speed up this process…?
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II. Solubility Curves and Guidelines
A. Table G: Solubility Guidelines for Aqueous Solutions
Supersaturated = ABOVEABOVE
Saturated = ONON the line
Unsaturated = BELOWBELOW
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B. Table F: Solubility Guidelines for Aqueous Solutions
These charts tell if an anion or cation is generally soluble in water
Exceptions occur for half of those listed
General rules of solubility here; not a total and complete list!
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Determine solubility…
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C. Net Ionic Equations
http://www.youtube.com/watch?v=RjBjwQF276ANet ionic equations are generated when ions
react within a solution to form a precipitate [solid]The ions involved in creating the solid will be
eliminated from the solution, eventuallyThe ions that are eliminated produce the “net”
reaction, or equation! [example on board]
http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s2_3.swf
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IV. Measuring Concentrations
A. Percent Mass (w/w)
B. Percent Volume (v/v)
C. Parts per Million (ppm)
D. Parts per Billion (ppb)
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Let’s practice…
What is the concentration of a solution, in parts per million, if 0.02 gram of NaCl is dissolved in 1000. grams of solution?
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Regents Practice Problems
An aqueous solution has 0.0070 gram of oxygen dissolved in 1000. grams of water.
------------------------------------------------------------
Calculate the dissolved oxygen concentration of this solution in parts per million.
[Your response must include both a correct numerical setup and the calculated result.]
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D. Molarity
moles solute
Molarity (M) = Liter solution
Solute MUST be in units of ‘moles’
Solvent MUST be in units of ‘Liters’
May use Molarity to find grams, moles, or molar mass
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Molarity Examples
1] Calculate the molarity of a solution containing 35.0g NaCl dissolved into 500mL of water.
2] How many grams of NaCl are needed to make 650mL of a 0.010M solution?
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E. Dilutions
Dilutions use Molarity and Volume to distribute the moles of a substance
McVc = MdVd
(Molarity) x (volume) in Liters = moles!Extremely useful equation!!!
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Dilution Examples
1] Calculate the new molarity of 1500.mL of solution made from 25.mL of 12M.
2] How much 18M acid is needed to make 2500mL of 0.10M solution?
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V. Colligative Properties
Colligative properties…
properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties/identity (e.g. size or mass) of the molecules
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Colligative properties
These include: lowering of vapor pressureelevation of boiling pointdepression of freezing point
They are based on the number of particles or electrolytes produced in a solution by a solute
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A. Electrolytes vs. Particles
Electrolytes are….
They conduct electricity!
Number of electrolytes formed per molecule depends on the # of ions it breaks into!
Ex.]
Particles are…
They DO NOT conduct electricity!
Produce only ONE particle per molecule dissolved!
Ex.]
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B. Factors Affected
1] Freezing Point DepressionFreezing Point Depression
Adding particles/electrolytes causes the freezing point of the solution to be less than that of the pure substance
Magnitude of change depends on # of particles/ions in solution
2] Boiling Point ElevationBoiling Point Elevation
Adding particles/electrolytes will cause the boiling point to increase for the solution
Can calculate the new boiling point using an equation
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Web demos
http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html
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2. Vaporization and Boiling
Vapor pressure = the pressure exerted by a layer of the gas phase on the surface of a liquid or solidHigh Vapor pressure = weaker IMF’s,
weaker bonds, changes to gas phase easilyLow vapor pressure = STRONGER IMF’s,
stronger bonds, and prefers to remain a liquid phase
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Table H Vapor Pressure of Four
Liquids
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3. Boiling Point vs. Normal Boiling Point
Boiling Point = temperature at which vapor pressure of the liquid equals the atmospheric pressure of the surroundings
NORMAL boiling point = temperature when the vapor pressure
equals standard pressure [1atm]
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What changes the boiling point?
Changes in atmospheric pressure cause changes in the boiling point
Low pressure at higher altitudes cause the boiling point to be lower than normal [pressure is lower than normal…]
High pressure occurring below sea level cause boiling points to increase […?]
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Vapor Pressure… REVIEW…
Vapor pressure changes INDIRECTLYINDIRECTLY with variations is atmospheric pressureExplain……
Vapor pressure is a function of IMF’s within the liquid phaseStronger IMF’s = lower vapor pressureWeaker IMF’s = higher vapor pressure
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VI. Acids and Bases
Acids = substances that react with a base; often has a low pH
May be strong or weak
Actual definition depends upon the type of acid/base
Bases = substances reacting with an acid; often has a high pH
May be strong or weak
3 major types of acids and bases here
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Properties of Acids and Bases
Acids: Taste sour Conduct current in
solution React with bases to
form water and salt React with some
metals to make H2(g)
Low pH
Bases: Taste bitter Slippery/soapy
feeling Conduct current in
solution React with acids to
form salt water Have low pOH or
high pH
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1. Arrhenius Acid/Base
Acid = substances that release hydrogen ions in aqueous solutions
proton donors
Ex.] HCl H+ + Cl-
Base = substances that release hydroxide ions in aqueous solutions
Hydroxide donors
Ex.] NaOH Na+ = OH-
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2. Bronsted-Lowry Acid/Base
Acid = any substance that can donate hydrogen ions in solution Proton donors
Ex.]
HCl H+ + Cl-
Base = any substance that can accept hydrogen ions in solution
Proton acceptors
Ex.]
NH3 + H+ NH4+
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Lewis Acids and Bases [non-Regents]
Acid = any species that can accept an electron pair from another species in solution
Ex.] H+ + NH3
Base = any species that can donate an electron pair to another species in solution
NH4+
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Weak vs Strong acids and bases
STRONG acids/bases will completely dissociate [ionize] in solution
Ex.] HCl, HNO3, H2SO4, NaOH, KOH, etc.
WEAK acids/bases produce very few ions per molecule in solution
Ex.] vinegar, H3PO4, formic acid, citric acid, etc.
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B. Conjugates
Acid/Base Conjugates = species that are formed in solution as a result of the dissociation of an acid or base
Ex.] HCl + NaOH Na+ + Cl- + HOH
Cl- is the conjugate base Na+ is the conjugate acid
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Acid-Base Reactions
Acid + Base = Salt + water
Acids and bases neutralize each other
H+ + OH- H2O
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C. pH and pOH
pH = the scale, 0-14, that defines the acidity or basicity of a solution Based on the concentration of hydrogen ions
0-6 = acid 7= neutral 8-14 = base
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pOHpOH = the measure of the concentration of OH- ions in solution
Opposite of pH
Scale 0-14 0-6 = strong base 7= neutral 8-14 = acidic
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Relating pH and pOH
pH + pOH = 14 always!
pH = -log[H+]
pOH = -log[OH-]
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D. pH and pOH Calculations
Ex. 1] What is the pH of a solution containing 9.15 x 10-6 M H+?
Ex. 2] What is the pH of a solution containing [OH-] = 8.11 x 10-5 M in 350.mL of solution?
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E. Indicators
Indicators = compounds that change color when the pH changes
Color changes indicate the pH of the solution!
Use several indicators to pinpoint the final pH!
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Indicators: Table M
Find the pH using the indicator and its color in the solution…
Tutorial on indicators:
http://www.kentchemistry.com/links/AcidsBases/Indicators.htm
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Expanded Indicators Chart
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F. Titrations
Titration = method used to determine the pH of an unknown solution
Process to find the concentration of an unknown acid/base by neutralizing it with a base/acid of known concentration
An indicator signals the equivalence point and tells that the neutralization is complete
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Titrations, [continued]
Uses burets, a standard solution of known pH, an indicator, and a fixed volume of a solution with an unknown pH
Titration Formula:
MaVa = MbVb