georgia performance standard sc7: students will characterize the properties that describe solutions...
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Georgia Performance Standard SC7: Students will characterize the properties that describe solutions and the nature of acids and
bases.
•Triatomic
•Covalent
•Polar bonds & polar overall
•Bent at 105° angle
Intermolecular ForcesPolar molecules
are attracted to one another by dipole forces
Water is attracted to other water molecules by a special dipole force, a hydrogen bond
Water Solutions“Chemically pure water never exists in
nature because water dissolves so many substances.” textbook
Universal solventAqueous solutions
Water SolutionsIonic compounds
most readily dissolve in water due to extreme polarity
Polar covalent compounds also dissolve in water
Nonpolar compounds don’t
Solvation of Ionic Compounds
A Few Exceptions...Remember the
solubility rules...In some ionic
compounds, the ions are so attracted to each other that they won’t break apart and dissolve.
These are INSOLUBLE ionic compounds.
Solvation of Covalent CompoundsCovalent compounds do NOT break apart in
water when dissolving.Solvation of covalent compounds means that
each solute molecule is surrounded by water molecules.
ConductorsIn general,
aqueous solutions of ionic compounds are electrolytes.
Generally, aqueous solutions of covalent compounds are nonelectrolytes.
Solution VocabularySolute: Dissolves in the solvent
Soluble: Able to be dissolved in the solvent (applicable to any states of matter)
Insoluble: Unable to be dissolved in the solvent (applicable to any states of matter)
Miscible: Able to be dissolved in the solvent (applicable to liquid/liquid solutions)
Immiscible: Unable to be dissolved in the solvent (applicable to liquid/liquid solutions)
Solubility VocabUnsaturated: less than maximum
amount of solute is dissolved in the solvent
Saturated: maximum amount of solute is dissolved in the solvent
Supersaturated: special conditions have been created to dissolve more than maximum amount of solute in the solvent
Determines IF Solute Will Dissolve...The nature of the solvent and solute
governs whether a solute will solvate in a particular solvent. Specifically, the nature of the intramolecular bond. Polar molecules will solvate with polar molecules. Nonpolar molecules will solvate with nonpolar molecules. BUT, polar and nonpolar will not form solutions together.
Determines Speed of Dissolving
1. Agitation: Create more collisions mechanically
2. Temperature: More kinetic energy creates more collisions
3. Surface Area: Dissolving process is a surface phenomenon, the more surface of the solute that is exposed the faster the solvation
BRING SOLUTE IN CONTACT WITH SOLVENT
Determines How Much Will Dissolve
1. Temperature: solubility of solid solute increases as the temp. increases; solubility of gaseous solute decreases as temp increases ex. Hot water bubbles, thermal pollution
2. Pressure: solubility of gaseous solute increases as the pressure increases
-Henry’s Law ex. Soft drinks
SOLUBILITY: HOW MUCH WILL DISSOLVE
Temperature & SolubilityHigher the
temperature, the more solid will dissolve in a liquid
Higher the temperature, the less gas will dissolve in a liquid
Henry’s Law: Pressure & Solubility
At a given temperature, the solubility of a gas is proportional to the pressure of the gas above the liquid.
Page 506
The higher the pressure, the more carbon dioxide will dissolve in the syrup giving a less “flat” taste.
Solubility Graph
Concentration of SolutionsThe concentration of a solution is a measure of
how much solute is dissolved in a specific amount of solvent or solution.
Molarity: most common units of solution concentration; # of moles solute dissolved in one liter of the solution
Molarity: moles of solute liter of solution
If given grams, remember to change it to moles.
Example 15.3 (page 531)
Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50L of solution.
Example 15.4 (page 532)
Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8 mL of solution.
molality: moles of solute kg of solvent
If given grams, remember to change it to moles.
The most common concentration term in chemistry is Molarity (M),
but chemists also report concentration in molality (m)
sometimes.
The front of the last page in the calculations packet refers to Molality. Complete 1 (a), 2 (a), 3 (b), and 4 (b).
NOTE: Questions 3 and 4 will require you to manipulate the equation. Question 4 might even require that you change the units of your answer at the end of the calculation.
Preparing a Solution in the LabYou’ve learned about concentration (Molarity
and molality). Therefore, you should be able to create your own solutions for use in the lab from now on.Example:
0.5 M HCl reacts with Mg(s) If I gave you HCl powder, what would you do to make
the solution? Watch these kids, and assess your plan. Choose a lab group and station. Draw an assignment
from the cup, and make the solution. Write your steps (including materials) as you go.
ALSO: Solve 15-2 Practice Problems WS 6, 8, 10-12, 14-16.
Diluting SolutionsIf you already have a solution molarity, but you
want a different molarity:Example: Your lab asks you to use 250 mL of 0.25M HCl, but you only find a jug of 6M HCl in the stockroom.
USE THIS EQUATION: M1V1 = M2V2
Example 15.8 (page 539)
What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H2SO4 solution?
*Be sure to solve the Dilution Worksheet in your practice packet!
Using Molarity as a Conversion FactorYou have learned to calculate molarity using
the equation: Molarity = moles of solute / liter of solution
Did you realize that the calculation is simply a ratio of solute to solution?
Ratios (ie mole ratios, energy to mole ratios) can be used as conversion factors in stoichiometry.
THEREFORE, molarity can be written into our dimensional analysis charts to solve stoichiometry problems.
Solutions StoichiometryWhat volume of 1.5 M HCl is needed to react with
21.5 grams of NaOH?What is the molarity of a solution of H2S if 48.5mL
are required to titrate 35.6mL of 0.35M Fe(OH)3 solution?
A white precipitate forms when 200 mL of 0.200M K3PO4 solution is mixed with 300 mL of 0.250 M CaCl2 solution. What mass of precipitate will form?
BE SURE TO SOLVE THE PRACTICE PROBLEMS IN YOUR PACKET!
Physical properties of solution are different from the physical properties of the solvent. Some properties are different simply because there are “foreign” particles (solute) in the solvent. Colligative properties of solutions depend only on the number of solute particles.
Boiling Point ElevationMore solute particles means that vapor
pressure is lower which means that more kinetic energy is needed to make vapor pressure equal atmospheric pressure!
Change in temperature is calculated:∆Tb = Kb m i
Since boiling point increases...ADD the change.
Kb will be given.
Freezing Point DepressionLiquid particles get into an orderly
pattern to become a solid. The solute particles disrupt the orderly pattern causing more kinetic energy to be drawn from the solution for it to freeze!∆Tf = Kf m i
Since freezing point decreases...SUBTRACT the change. Kf will be given
About.com Chemistry Ice has to absorb energy in order to melt, changing the
phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using 'ice cream salt', which is just salt sold as large crystals instead of the small crystals you see in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.
MolalityAnother unit for concentrationm=moles of solute per kilogram of solventpage 520
Solutions StoichiometryA white precipitate forms when 200 mL of
0.200M K3PO4 solution is mixed with 300 mL of 0.250 M CaCl2 solution. What mass of precipitate will form?
What volume of 1.5 M HCl is needed to react with 21.5 grams of NaOH?
What is the molarity of a solution of H2S if 48.5mL are required to titrate 35.6mL of 0.35M Fe(OH)3 solution?