chem 1151: ch. 7 solutions and colloids. seager sl, slabaugh mr, chemistry for today: general,...
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Chem 1151: Ch. 7
Solutions and Colloids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011; http://en.wikipedia.org/; http://www.medfinity.com/index.php?cPath=704_737
Solutions: Homogeneous mixtures of two or more substancesParticles uniformly distributed and transparent (clear)Particles in constant motion (KE), don’t settle under influence of gravity
Solution = Solvent + Dissolved Solute
Solvent is most abundant substance comprising solutionSolute(s) is/are other substance(s) that are not the solvent
Solutions usually liquids but may be gases or solids
Physical States of SolutionsPhysical States of Solutions
SolubilitySolubilitySoluble substances: Dissolve completely in solventInsoluble substances: Do not dissolve in solventImmiscible: Liquid solute that does not dissolve in a liquid solvent
The extent of solubility can varyIsopropyl alcohol and water are completely soluble in any proportionLimit on how much sugar will dissolveOil and water form distinct, separate layers
Saturated solution: Solution with max amount of dissolved soluteSupersaturated solution: Solutions where amount of solute dissolved is greater than solute solubility
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Calcium carbonate
SupersaturationSupersaturationPreparation of a Supersaturated solution1.Form a nearly saturated solution at high temp (higher solubility)
• Cool solution to lower temperature (lower solubility)2.“Seed” the solution with some solid solute excess solute (above saturation) crystallizes3.The remaining solution is saturated
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011;http://www.myrecipes.com/recipe/rock-candy-10000001176193/
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Solubility of gases in water decreases as temp increases CO2 is less soluble in warm soda than cold soda
Gas solubility is directly proportional to gas pressure If gas pressure is doubled, solubility is doubled
Effects of Pressure and Temperature on Gas SolubilityEffects of Pressure and Temperature on Gas Solubility
Ex.1 Why your champagne is bubblyCold champagne (wine) is saturated with CO2, sealed under pressurePressure is relieved when bottle opened
Ex.2 The bendsDivers breath air under pressure that causes N2 to be more soluble in blood than occurs at 1 atmIf divers swims to surface too fast, N2 bubbles form in blood and joints
Joint pain Paralysis Death
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
When solid, ionic compounds placed in water, polar water molecules orient themselves by charge along surface of solid
Produces a shielding effect, allows water to remove ions from matrix (i.e., ions become hydrated)
Hydrated ions become evenly distributed throughout solution
Formation of SolutionsFormation of Solutions
Process continues until number of ions in solution results in saturation.
Ions begin to reform solid equilibrium.
Similar results are observed with polar, non-ionic solids (e.g., sugar)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Two reasons why solute won’t dissolve in solvent:1.Forces between solute particles stronger than solvent particles2.Solvent particles more attractive to each other than solute particles
“Like dissolves like”Polar molecules dissolve in polar solvents (e.g., water)Non-polar molecules dissolve in non-polar solvents (e.g., CCl4)
Formation of a SolutionFormation of a Solution
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Predict the solubility of the following:1.NH3 in water2.O2 in water3.Ca(NO3)2 in water4.Mg3(PO4)2 in water5.Paraffin wax (nonpolar) in CCl4
6.BaCO3 in water7.Li3PO4 in water
Predicting SolubilityPredicting Solubility
1.Soluble, NH3 is polar2.Insoluble, O2 is nonpolar3.Soluble4.Insoluble5.Soluble6.Insoluble7.Soluble
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
Insoluble compounds may be soluble over long periods of time (chemical weathering)Normally soluble solutes may dissolve slowly (rock candy dissolves slower than granulated sugar)Dissolving rate may be increased1.Crushing or grinding solute (increases surface area exposure)2.Heating solvent (molecules move faster, more collisions)3.Stirring or agitating
Rate of SolubilityRate of Solubility
Heat is usually absorbed or released when solute dissolves in solvent1.In endothermic processes, heat is absorbed by interaction between solute and solvent molecules
Removes heat from bulk solvent2.In exothermic processes, heat is release by interaction between solute and solvent molecules
Adds heat to bulk solvent
Heat of SolubilityHeat of Solubility
Concentration: How much solute is in a solvent
Solution ConcentrationsSolution Concentrations
Molarity
Percentage
% w/w
% w/v
% v/v
2.00 L of solution contains 1.50 mol of solute.
Calculating Solution Concentrations (Molarity)Calculating Solution Concentrations (Molarity)
Molarity
150 mL of solution contains 0.210 mol of solute.
315 mL of solution contains 10.3 g of C3H7OH.
A solution contains 100 g of water and 1.20 g of solute. What is the %(w/w) concentration?
Calculating Solution ConcentrationsCalculating Solution Concentrations
% w/w
A solution is made by mixing 90.0 mL of alcohol with enough water to give 250.0 mL of solution. What is the %(v/v) concentration of alcohol in the solution?
A 150.0 mL sample of saltwater is evaporated to dryness. A residue of salt weighing 27.9 g is left behind. Calculate the % (w/v) of the original saltwater.
Calculating Solution ConcentrationsCalculating Solution Concentrations
A solution is made by dissolving 0.900 g of salt in 100.0 mL of water. Assume that 1.0 mL of water weighs 1.00 g, and the final solution volume is 100.0 mL. Calculate the %(w/w) and %(w/v) for the solution.
Method 1: Mix solute and solventMethod 2: Dilute a concentrated solution with solvent
Solution PreparationSolution Preparation
Moles/L%(w/w)%(v/v)%(w/v)
Measurements may be volumetric, gravimetric or both, depending on your concentration objective
Mass may be converted by volume based on density, so that volume can be measured, not mass
Volume not as accurate as mass
D = m/V
Solution PreparationSolution Preparation
Describe how to prepare 1.00 L of 1.50 M CoCl2 solution
Describe how to prepare 1.50 L of 0.50 M CoCl2 solution
Describe how to prepare 200 mL of 0.200 M CoCl2 solution
Describe how to prepare 500 mL of 1.6 × 10-4 M Pb(NO3)2 solution
Solution PreparationSolution PreparationDescribe how to prepare 250 mL of 0.900% (w/v) NaCl solution
Describe how to prepare 100 mL of 12.0% (w/v) MgCl2 solution
Solution Preparation - DilutionSolution Preparation - Dilution
This equation works for any form of concentration based on volume
Describe how to prepare 250 mL of 0.100 M NaCl solution from 2.00 M NaCl
Describe how to prepare 500 mL of 0.250 M NaOH solution from 6.00 M NaOH
Solution StoichiometrySolution Stoichiometry Stoichiometry deals with relative quantities of reactants and products in
balanced chemical equation We can now apply everything learned about mass, moles,
concentrations and balancing equations to solutions
Ex. 01: What volume of 0.200 M NaOH solution is needed to exactly react with 0.150 moles of HCl?
We need 0.150 moles of NaOH for 0.150 moles of HCl (1:1 stoichiometry)NaOH solution is 0.200 M (moles/L)
Solution StoichiometrySolution Stoichiometry
Ex. 01: What volume of 0.185 M NaOH solution is needed to exactly react with 25.0 mL of 0.255 M HCl?
We need to figure out moles in 25.0 mL of 0.255 M HCl
Now we can find volume of of 0.185 M NaOH from moles HCl and stoichiometry
Solution Properties – Electrical ConductivitySolution Properties – Electrical ConductivityElectrolytes: Solutes that form water solutions capable of conducting electricitySolutes dissociate to form ions
Strong Electrolytes (e.g., HCl) dissociate completely, strong conductorsWeak Electrolytes (e.g., Acetic acid) dissociate slightly, weak conductors
Electrolytes maintain precise osmotic gradients at the cellular level. These regulate body hydration and blood pH, and are critical for nerve and muscle function.
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Colligative PropertiesColligative PropertiesDepend only on concentration of solute particles present, not identity of soluteSolutions containing 1 mol sugar and 1 mol salt would have identical colligative propertiesClosely-related colligative properties include:
Vapor pressure Boiling point (BP) Freezing point (FP)
Colligative properties differ between solutions and pure solvents:Vapor pressure of water (solvent) above solution is lower than vapor pressure of pure waterCauses higher BP and lower FP of solutions, compared with pure solventThese differences can be calculated with the following equations:
m = solution molality (same as molarity for dilute solutions)K = Derived constant (°C/M) related to BP or FP of solventn = number solute moles in solution when 1 mol solute dissolves
Colligative Property: Osmotic PressureColligative Property: Osmotic Pressure Water can pass through membrane but sugar cannot Net flow into sugar side to increase vapor pressure Continues until osmotic pressure balances tendency of water to flow to
sugar side (until equilibrium)
In general, net flow of solvent through semipermeable membranes is always from more dilute solution into more concentrated solution
Osmotic pressure can be calculated with the following:
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011
ColloidsColloids Similar to solutions
Homogeneous mixtures of 2 or more components More of one component than others
Colloids defined by: Dispersing medium: Like solvent Dispersed phase: Like solute
Main differences: Colloids have much larger particles (up to 10X larger) than solutions Gives them cloudy appearance
Colloids: Glues Gels (shaving cream) Cheese