unit 7: solutions, acids, & bases. i. definitions and types of solutions a. what exactly is a...
Post on 25-Dec-2015
217 Views
Preview:
TRANSCRIPT
Unit 7:
Solutions,
Acids, & Bases
I. Definitions and Types of Solutions
A.What exactly IS a Solution?
B. Types:
[Vocabulary terms…]1] Unsaturated
2] Saturated
3] Supersaturated
4] Suspensions
5] Colloids
6] Alloys
Question…
HOW do we create solutions?
C. Forming Solutions
Polar solvents mix best with __________solutes!
How do IMF’s relate to this concept?
Nonpolar solvents mix best with ________________ solutes!
Examples…
Like Dissolves Like…
See Table 7.1 on pg. 119 of Review book!
SoluteNonpolar Solvent
Polar Solvent
Nonpolar
Polar
Ionic
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?
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!
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
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
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
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…?
II. Solubility Curves and Guidelines
A. Table G: Solubility Guidelines for Aqueous Solutions
Supersaturated = ABOVEABOVE
Saturated = ONON the line
Unsaturated = BELOWBELOW
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!
Determine solubility…
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
IV. Measuring Concentrations
A. Percent Mass (w/w)
B. Percent Volume (v/v)
C. Parts per Million (ppm)
D. Parts per Billion (ppb)
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?
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.]
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
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?
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!!!
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?
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
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
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.]
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
Web demos
http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/propOfSoln/colligative.html
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
Table H Vapor Pressure of Four
Liquids
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]
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 […?]
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
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
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
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-
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+
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+
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.
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
Acid-Base Reactions
Acid + Base = Salt + water
Acids and bases neutralize each other
H+ + OH- H2O
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
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
Relating pH and pOH
pH + pOH = 14 always!
pH = -log[H+]
pOH = -log[OH-]
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?
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!
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
Expanded Indicators Chart
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
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
top related