CHAPTER 13 Mixtures and Concentrations

Types of Mixtures Solutions Suspensions Colloids

Solutions Soluble –Capable of being dissolved Solution –Homogenous mixture – thoroughly mixed Solvent –Dissolving medium – “doing” the dissolving –Often Water = the universal solvent Solute –Substance being dissolved Example – Sugar Water

Solutions Electrolyte –Conducts electric current when in solution –Example – NaCl – IONICS, Acids, Bases Nonelectrolyte –Does NOT conduct electricity –Example – Sugar – MOLECULAR SUBSTANCES

Solutions Types of solutions –Gas solutions Gas with gas – quickly intermingle – air Constant motion –Liquid solutions Liquid with gas – Soda (CO 2 in sugar water) Liquid with liquid – Vinegar (acetic acid + water) –Solid solutions Alloy – two or more metals are mixed –Sterling silver (Cu + Ag) –Brass (Cu + Zn) –Bronze (Cu + Sn)

Solutions Evidence that it is a solution –Cannot be filtered –NO light scattering

Suspensions Heterogeneous mixture with particles that settle out –Water particles are not strong enough to keep other particles from settling out –Example - Muddy water Evidence that it is a suspension –Can be filtered –Particles settle –May scatter light –Not transparent

Colloids In-between a solution and a suspension –Medium size particles –Small enough to be kept in “permanent” suspension Dispersed phase –Solute-like particles Dispersing phase –Solvent-like particles

Colloids Evidence that it is a colloid –Scatters light –Does not settle Tyndall Effect –Light scattered by colloidal particles Examples – Jello; Cool Whip Time: 5:39-6:26

Making Solutions Factors affecting rate of dissolving – ways to speed up dissolving –Increase surface area of solute More solute touches solvent Ex – crush, spread out –Agitate solution Spreads out already dissolved solute to bring in more fresh solvent in contact with solute Ex – stir, shake –Heat solvent Particles move faster as energy increases More collisions between solute and solvent

Solubility Solution equilibrium – opposing rates of dissolving and crystallizing are equal –Unsaturated Contains less than maximum amount of solute –Saturated Contains maximum amount of solute More will NOT dissolve –Supersaturated Has more solute than a saturated solution at same conditions

Supersaturated solutions Steps to make –Heat saturated solution –Add more solute –Cool slowly –Addition of one more crystal? Will crystallize entire solution!! Video

Factors affecting solubility Solubility = Ability to dissolve Type of solute/solvent –“like dissolves like” –Immiscible – Liquids NOT soluble in each other Water and oil –Miscible – Liquids are soluble in each other Vinegar

Factors affecting solubility Pressure –Increase pressure = increase amount of gas dissolved –Example – Soda –Henry’s Law Increase pressure = Increase solubility of a gas

Factors affecting solubility Temperature –If solute is gas Increase temp = Decrease solubility –If solute is solid usually… Increase temp = Increase solubility

Heat of Solution Amount of energy released/absorbed when solute dissolves in solvent (kJ/mol) –Endothermic Absorbs heat Positive (+) heat of solution –Exothermic Releases heat Negative (-) heat of solution –Solvated – solute particles surrounded by solvent

Bond changes during solution formation Solute-solute attractions broken –REQUIRES ENERGY Solvent-solvent attractions broken –REQUIRES ENERGY Solute-solvent attractions formed –RELEASES ENERGY

Compare energies Process is ENDOTHERMIC if: –Steps > Step 3 Process is EXOTHERMIC if: –Step 3 > Steps 1 + 2

Concentrations Percent by Mass Mole Fraction (needs to be added) Molarity (M) Molality (m)

Percent by mass % Mass = Mass solute x 100% Mass total solution Solution = solute + solvent !!!! Examples

Mole Fraction Mole Fraction (X) = Moles substance A Total moles solution Examples

Molarity Molarity (M) = Moles solute Liters solution Examples

Molality Molality (m) = Moles solute kg solvent Examples

Colligative Properties A property that depends of number of solute particles –Vapor-Pressure Lowering –Boiling Point Elevation –Freezing Point Depression Nonvolatile – a substance that does NOT evaporate very much

Vapor-Pressure Lowering Adding a nonvolatile substance lowers the vapor pressure –Increase solute = Decrease VP SIMPLIFIED Reason – Less solvent at the surface

Boiling Point Elevation Increase solute = Increase BP –Boiling occurs when VP = P atm –If VP is lowered by adding a solute, it will take more energy to make VP = P atm, so the temperature will be higher –Ex – Add salt to cook (not enough to notice, though)

Boiling Point Elevation ∆T = K b * m –K b = Boiling point elevation constant –K b of water = 0.51°C/m Examples

Freezing Point Depression Increase solute = Decrease FP –When freezing occurs, the solvent solidifies –Adding solute, you must cool the solution to a lower temp to freeze –Ex – antifreeze, salt on roads (most now also give off heat), homemade ice cream - htm htm

Freezing Point Depression ∆T = K f * m –K f = Freezing Point Depression Constant –K f of water = 1.86°C/m Examples

Molar Mass Calculations Steps: 1. Use ∆T = K * m to find m 2. Use m equation to find moles solute 3. Use MM = mass solute / moles solute to find MM Examples: