Factors Affecting Solubility As To , rate 1. temperature As size , rate 2. particle size More mixing, rate 3. mixing 4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

Measuring Concentration Concentration…a measure of solute-to-solvent ratio concentrated vs. dilute “lots of solute” “not much solute” “watery” Add water to dilute a solution; boil water off to concentrate it.

Measuring Concentration “The amount of solute in a solution” A. Parts per million (ppm)  also, ppb and ppt = g solute/1,000,000 g solution – commonly used for minerals or contaminants in water supplies B. Molarity (M) = moles of solute L of solution – used most often mol L M C. Molality (m) = moles of solute kg of solvent

One mole, in solution.

Molarity liter of solution

Molarity Find the molarity of a solution containing 75 g of MgCl2 in 250 ml of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 L water = 3.2M MgCl2

Molality mass of solvent only 1 kg water = 1 L water

Molality Find the molality of a solution containing 75 g of MgCl2 in 250 ml of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

Molality How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

Factors Affecting Solubility As To , rate 1. temperature As size , rate 2. particle size More mixing, rate 3. mixing 4. nature of solvent/solute (“like dissolves like”, polar dissolves polar)

Solubility (“Dissolution”) Temperature -The solubility of most solids in water increases as the temperature of the sol’n increases. -The solubility of gases in water decreases with increasing temperature

Solubility (“Dissolution”) Experiment 1: Add 1 drop of red food coloring Before AFTER Miscible – “mixable” two gases or two liquids that mix evenly Water COLD Water HOT Water COLD Water HOT You should observe that temperature effects the rate of solution. As the temperature of the liquid solvent increases, the molecules move faster, and the food coloring dissolves more quickly. A B A B 12

Solubility (“Dissolution”) Experiment 2: Add oil to water and shake AFTER Before Immiscible – “does not mix” two liquids or two gases that DO NOT MIX Oil You should observe that for solutions to mix they must be chemically similar. Polar and polar molecules will mix, non-polar and non-polar molecules will mix, but polar and non-polar molecules will not mix. The reasons for this will be explained later. Remember, ‘like dissolves like’. polar dissolves polar non-polar dissolves non-polar Water Water T0 sec T30 sec 13

Gas Solubility Higher Temperature …Gas is LESS Soluble CH4 O2 2.0 O2 Higher Temperature …Gas is LESS Soluble Solubility CO 1.0 The general rule of thumb is that the solubility of gases decreases when temperature increases. He 10 20 30 40 50 Temperature (oC)

Solubility: forming a “saturated” solution in equilibrium UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form increasing concentration

“Oil and Water Don’t Mix” Oil is nonpolar Water is polar “Like dissolves like”, nonpolar dissolves nonpolar, nonpolar does not dissolve polar Lycopodium Powder demonstration. Lycopodium powder is a nonpolar hydrocarbon that doesn’t mix with water. It is dry to the touch and not oily feeling. Sprinkle lycopodium powder on top of a beaker of water. Slowly, push your finger through the surface of the lycopodium powder into the water. Slowly withdraw your finger, it remains dry the entire time. Why? Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 470

Water Molecule H2O d+ d+ d- d- Water is a POLAR molecule O2- H+ H+ Draw the Lewis dot structure of a water molecule. Recall, oxygen has 6 valence electrons and hydrogen has one valence electron. The ‘electron cloud’ is more dense around the oxygen than the hydrogen. Therefore, the oxygen side of the molecule is more negatively charged and has a partial negative charge. The hydrogen have a lower electron density around them and receive a partial positive charge. This molecule does not have a formal (+) and (-) charge – as in an ionic compound.

Dissolving of NaCl in Water ions Na+ Water molecules When sodium chloride crystals are dissolved in water, the polar water molecules exert attracting forces which weaken the ionic bonds. The process of solution occurs the ions of sodium and chloride become hydrated. NaCl(s) + H2O  Na+(aq) + Cl-(aq)

Ethanol is Polar d - O d + Polar bond C C H H H H H H Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 469

Ethanol and Water are Soluble C ‘Like dissolves like’ Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 469

Lava Lamp a philosophy an art form progressive post-modern

Cleaning Action of Soap Micelle Timberlake, Chemistry 7th Edition, page 573

MODEL OF A SOAP MOLECULE emulsifying agent (emulsifier): -- molecules w/both a polar AND a nonpolar end -- allows polar and nonpolar substances to mix e.g., soap detergent lecithin eggs MODEL OF A SOAP MOLECULE Na1+ NONPOLAR HYDROCARBON TAIL POLAR HEAD

Interstitial Spaces Oil Non-polar "immiscible" Polar dissolved solid Layer Water Water Polar This is an overly simplified model of spaces between water molecules. However, it is in these interstitial spaces that gases (e.g. oxygen and carbon dioxide) dissolve and solids also dissolve. red food coloring

Clogged Pipes – Hard Water Step 1: Acid rain is formed H2O + CO2 H2CO3 carbonic acid Step 2: Acid rain dissolves limestone H2CO3 + CaCO3 Ca(HCO3)2 Water softner H2CO3 + MgCO3 Mg(HCO3)2 ‘hard’ water

Pipes develop Scales Ca(HCO3)2 CaCO3(s) + H2O + CO2 Step 3: Hard water is heated and deposits scales Ca(HCO3)2 CaCO3(s) + H2O + CO2 Mg(HCO3)2 MgCO3(s) + H2O + CO2 D scales on pipes D

Water Purification Cation Exchanger Anion Exchanger Hard Water Deionized Water H+ OH- H+ OH- H+ Mg2+ OH- Na+ H+ (a) (b) OH- (c) OH- Fe3+ Ca2+ H+ H+ OH- H+ In some areas of the country, the minerals dissolved in water give it a high concentration of various ions that make the water suitable neither for drinking nor for agriculture. Such water is called hard water. Sometimes the mineral content in hard water is so great that it causes plumbing and corrosion problems. Hard water typically contains a high concentration of the following ions: Ca2+, Mg2+, Fe3+, Cl1-, CO32-, SO42-, and PO43-. Water is deionized (softened) by removing the minerals using an ion exchange system. Water is passed through a resin that has both cation and anion exchange components. First, cations such as Na+ in the water are exchanged for hydrogen ions on the resin. Second, anions such as Cl- in the water are exchanged for hydroxide ions. The net result is that the resin removes all ions from water passing through the deionizing system. OH- H+ OH- Hard water is softened by exchanging Na+ for Ca2+, Mg2+, and Fe3+. The cations in hard water are exchanged for H+. The anions in hard water are exchanged for OH-. The H+ and OH- combine to give H2O. Corwin, Introductory Chemistry 2005, page 361

Pure water does not conduct an electric current Source of electric power Pure water Pure water doesn’t conduct electricity because it contains no ions. Ions (cations have (+) charges) carry electrons in solution. The flow of electrons is called electricity. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

Ionic Solutions conduct a Current Source of electric power Free ions present in water To make a solution that conducts electricity (an electrolyte) – an ionic salt is added. An alternative method is to add acid. In truth, most acids are oxysalts dissolved in water. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 215

electrolytes: solutes that dissociate in solution -- conduct electric current because of free-moving ions e.g., acids, bases, most ionic compounds -- are crucial for many cellular processes -- obtained in a healthy diet -- For sustained exercise or a bout of the flu, sports drinks ensure adequate electrolytes. nonelectrolytes: solutes that DO NOT dissociate -- DO NOT conduct electric current (not enough ions) e.g., any type of sugar

Strong electrolytes exhibit nearly 100% dissociation. NaCl Na1+ + Cl1– NOT in water: 1000 0 0 in aq. solution: 1 999 999 Weak electrolytes exhibit little dissociation. CH3COOH CH3COO1– + H1+ NOT in water: 1000 0 0 in aq. solution: 980 20 20 “Strong” or “weak” is a property of the substance. We can’t change one into the other.

Electrolytes Electrolytes - solutions that carry an electric current strong electrolyte weak electrolyte nonelectrolyte NaCl(aq) Na+ + Cl- HF(aq) H+ + F- Timberlake, Chemistry 7th Edition, page 290

Colligative Properties  depend on concentration of a solution Compared to solvent’s… a solution w/that solvent has a… …normal freezing point (NFP) …lower FP FREEZING PT. DEPRESSION …normal boiling point (NBP) …higher BP BOILING PT. ELEVATION 33

Applications (NOTE: Data are fictitious.) 1. salting roads in winter FP BP water 0oC (NFP) 100oC (NBP) water + a little salt –11oC 103oC water + more salt –18oC 105oC 2. antifreeze (AF) /coolant FP BP water 0oC (NFP) 100oC (NBP) water + a little AF –10oC 110oC 50% water + 50% AF –35oC 130oC Why do you think some towns use calcium chloride on roads in the winter versus sodium chloride? CaCl2 yields three ions while NaCl yields only two ions. Calcium chloride will work in colder weather. Calcium chloride will work better than sodium chloride. Secondly, calcium chloride doesn’t kill grass like sodium chloride.

Effect of Pressure on Boiling Point Boiling Point of Water at Various Locations Location Feet above sea level Patm (kPa) Boiling Point (C) Top of Mt. Everest, Tibet 29,028 32 70 Top of Mt. Denali, Alaska 20,320 45.3 79 Top of Mt. Whitney, California 14,494 57.3 85 Leadville, Colorado 10,150 68 89 Top of Mt. Washington, N.H. 6,293 78.6 93 Boulder, Colorado 5,430 81.3 94 Madison, Wisconsin 900 97.3 99 New York City, New York 10 101.3 100 Death Valley, California -282 102.6 100.3