II III I Thanks to C. Johannesson The Nature of Solutions Solutions

Matter Flowchart MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes ColloidsSuspensions IPC-Solutions-Borders

A. Definitions  Solution -  Solution - homogeneous and stable mixture  Aqueous solutions: solution where something has been dissolved in water Solvent Solvent - present in greater amount. Water is the universal solvent Solute Solute - substance being dissolved. The substance in the smaller amount

C. Johannesson A. Definitions Solute Solute - KMnO 4 Solvent Solvent - H 2 O

C. Johannesson

Prentice-Hall © 2002General Chemistry: Chapter 14Slide 6 of 46 Solution Formation and Equilibrium saturated The rate of dissolving = rate of crystallization

C. Johannesson B. Solvation  Solvation – A chemical reaction between the solute and the solvent whereby a solution is formed.  Solvation – the process of dissolving. A chemical reaction between the solute and the solvent whereby a solution is formed. solute particles are separated and pulled into solution solute particles are surrounded by solvent particles

C. Johannesson B. Solvation  Dissociation  Dissociation: separation of an ionic solid(crystal) into it component ions through the breakdown of the crystal lattice NaHCO 3 (s)  Na + (aq) + HCO 3 –1 (aq)

Na + Cl - NaCl solid salt NaCl (aq) = Na + = Cl - Dissolving of solid NaCl Animation by Raymond Chang All rights reserved.

Polar water molecules interact with positive and negative ions Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 468 Animation

C. Johannesson B. Solvation NONPOLAR POLAR General rule: Polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes “Like Dissolves Like” General rule: Polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes “Like Dissolves Like”

Water HOT Solubility A B Before Water COLD Add 1 drop of red food coloring Miscible – “mixable” two gases or two liquids that mix evenly Experiment 1: Water HOT AFTER Water COLD A B

Solubility Water Oil T 30 sec AFTER Before Add oil to water and shake Immiscible – “does not mix” two liquids or two gases that DO NOT MIX Experiment 2: T 0 sec

C. Johannesson Solvation Strong Electrolyte Non- Electrolyte solute exists as ions only. Conducts current - + salt - + sugar solute exists as molecules only. Does not conduct electric current - + acetic acid Weak Electrolyte solute exists as ions and Molecules. Doesn’t conduct well DISSOCIATIONIONIZATION View animation online.animation

Solution, Suspension, Colloid Timberlake, Chemistry 7 th Edition, page 309

Suspensions: mixture from which the particles settle out when it is allowed to stand -are heterogeneous because you can see at least two different substances -particles are large enough to be filtered out -the large size of the particles(when compared to solutions) is why they settle out if the suspension is left to stand -Example: mud and water, some medications

Colloids: heterogeneous mixtures containing particles of intermediate size that remain suspended in the mixture. -generally appear milky or cloudy when concentrated but relatively clear when dilute -Particles are too small to be filtered out and they remain suspended in the mixture(they don’t settle out) -The particles are large enough to scatter light -Example: milk solids in water

Tyndall Effect Put a beam of light through a mixture Reflection of light off undissolved particles A) Solution - no Tyndall effect- can’t see the beam B) Suspensions - sparkle off big particles C) Colloids – continuous beam A B C

Brownian Motion Chaotic movement of colloidal particles caused by the collision of the particles with the solvent in which they are dispersed-this causes them not to settle.

Matter Flowchart MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompoundElement MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes ColloidsSuspensions

Types of Solutions SoluteSolventSolution Gaseous Solutions gas liquid gas air (nitrogen, oxygen, argon gases) humid air (water vapor in air) Liquid Solutions gas liquid solid liquid carbonated drinks (CO 2 in water) vinegar (CH 3 COOH in water) salt water (NaCl in water) Solid Solutions liquid solid dental amalgam (Hg in Ag) sterling silver (Cu in Ag) Charles H.Corwin, Introductory Chemistry 2005, page 369

Solid Brass An alloy is a homogeneous mixture of metals. Brass = Copper + Zinc Solid brass homogeneous mixture Copper Zinc

As size, rate Allows more solute particles to be in contact with solvent particles As T o, rate More collisions with solute and solvent 3. mixing/agitation Factors Affecting the Rate of Dissolution 1. temperature 2. particle size More mixing, rate not the quantity

C. Johannesson Solubility  Solubility maximum grams of solute that will dissolve in 100 g of solvent at a given temperature and pressure varies with temp based on a saturated solution

Degree of saturation Saturated solution  Solvent holds as much solute as is possible at that temperature.  Undissolved solid remains in flask.  Dissolved solute is in dynamic equilibrium with solid solute particles. IPC-Solutions-Borders

Saturated Solution IPC-Solutions-Borders

Saturation Types saturated A solution containing the maximum amount of solute for a given amount of solute at constant temperature and pressures; an equilibrium exists between the solution and any undissolved solute. unsaturated solution containing less than the maximum amount of solute supersaturated solution containing more solute than is normally allowed

C. Johannesson Solubility SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Degree of saturation Supersaturated Solution  Solvent holds more solute than is normally possible at that temperature. An essential condition for the growth of crystals  These solutions are unstable; crystallization can often be caused by adding a “seed crystal” or scratching the side of the flask.

.. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate. IPC-Solutions-Borders

C. Johannesson Solubility  Solubility Curve shows the dependence of solubility on temperature

Temp. ( o C) Solubility (g/100 g H 2 O) KNO 3 (s) KCl (s) HCl (g) SOLUBILITY CURVE Solubility  how much solute dissolves in a given amt.of solvent at a given temp. below unsaturated:solution could hold more solute; below line on saturated:solution has “just right” amt. of solute; on line supersaturated:solution has “too much” solute dissolved in it; above the line

Solubility of Sodium Acetate Temperature ( o C) Solubility(g/100 g H 2 O) Supersaturated solution Unsaturated solution Saturated Video Clip Charles H.Corwin, Introductory Chemistry 2005, page 378 A single crystal of sodium acetate, NaC 2 H 3 O 2, is dropped into a supersatureated solution The small crystal causes extensive crystallization, and eventually the solute forms a solid mass of NaC 2 H 3 O 2.

C. Johannesson Solubility  Solids are more soluble at... high temperatures.  Gases are more soluble at... low temperatures & high pressures (Henry’s Law). EX: nitrogen narcosis, the “bends,” soda

Solid Solubility vs. Temperature Timberlake, Chemistry 7 th Edition, page 297 KI NaNO 3 KNO 3 Na 3 PO 4 NaCl Temperature ( o C) Solubility (g solute / 100 g H 2 O)

Gas Solubility CH 4 O2O2 CO He Temperature ( o C) Solubility (mM) Higher Temperature …Gas is LESS Soluble

Gases in Solution The solubility of liquids and solids does not change appreciably with pressure. But, the solubility of a gas in a liquid is directly proportional to its pressure. Increasing pressure above solution forces more gas to dissolve. IPC-Solutions-Borders

Prentice-Hall © 2002General Chemistry: Chapter 14Slide 38 of 46 Henry’s Law Solubility of a gas increases with increasing pressure. S 1 /P 1 = S 2 /P g/ml 3.5 atm = S2S atm = 0.22 ml g/L Rearrange the formula and substitute in and solve or show all algebra work!

Real world applications : Henry’s Law and soda  The quantity of gas dissolved in a liquid depends directly on the pressure of that gas above the liquid  Under pressure the CO 2 in the liquid is kept in solution  Open the cap and the CO 2 rapidly escapes

Prentice-Hall © 2002General Chemistry: Chapter 14 Henry’s Law

Questions… 1. How does the solubility of a gas affected by pressure above the liquid? 2. What could you do to change: –(A) a saturated solution to unsaturated? –(B) an unsaturated solution to a saturated solution? 3. Can a solution with undissolved solute at the bottom be supersaturated?