Chem 1151: Ch. 7 Solutions and Colloids. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011;

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

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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


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


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)


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


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


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:


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

Documents

Chem 1151: Ch. 7 Solutions and Colloids. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7 th Edition, 2011;