Solutions & Concentration

Water  Polar molecule w/ polar bonds  Causes surface tension & ability to dissolve polar molecules and ionic compounds

Solutions  a.k.a. homogeneous mixture  Solutions can exist in any of the phases of matter.  Gases = Air (Nitrogen and Oxygen)  Liquids = Vinegar (Water and Acetic Acid)  Solids = Steel (Iron and Carbon)

What happens at the molecular level? The solvent molecules surround the solute molecules, in a process called solvation. Random motion of molecules causes mixing Go to animation

Ionic compounds  Ions dissociate when they dissolve!  This is what allows them to conduct electricity when dissolved  Called electrolytes

Heterogeneous Mixtures  Suspensions - mixture with large particles that settle out if left undisturbed  Colloids - mixture with medium size particles… larger than solution particles, but smaller than suspension particles

Amounts of Solute  Specific amounts of solute can be dissolved at each temperature and pressure.  Unsaturated = more solute can dissolve  Saturated = maximum amount of solute dissolved  Supersaturated = more than maximum amount is dissolved  Achieved by increasing temperature, adding solute, then slowly bringing temperature back down. Sodium acetate demo!

^ supersaturated ^ unsaturated sToP & tHinK: If you have 20 grams of KNO 3 in 100 g of H 2 O at 50 C, is it unsaturated, saturated, or supersaturated?

1) How many grams of NaNO 3 can dissolve in 100 g of water at 10 C? 2) At what temperature can 80 grams of KNO 3 dissolve into100 grams of water? 3) How many grams of KNO 3 can dissolve into 50 g of water at 40 C?

To Mix or Not To Mix… Not all substance combinations dissolve! Depends on polarity/charge…  For a solid/gas solute in a liquid solvent: If it dissolves…soluble If it doesn’t…insoluble  For a liquid solute in a liquid solvent: If it dissolves…miscible If it doesn’t…immiscible Oil / water

Factors that Affect Solubility SOLID SOLUTE   the temperature =  solubility (usually, but NOT always)   the surface area =  solubility GAS SOLUTE   temperature =  solubility   the pressure =  solubility (like in the gas in soda pop lab!) Alka-seltzer demo

Solubility Video (5 min)

Calculating Concentration 1. Molarity (M) 2. percent composition (%) 3. parts per million (ppm) 4. grams/liter (g/L)

Molarity  M = moles of solute / liters of solution  Example: What is the molarity of 5 moles of iodine dissolved in water, making 50 L of solution?

2 fish / 2 Liter 2 fish / 4 Liter Molarity looks at the number of solute particles / volume of solution

Percent Composition  percent by mass = (mass of solute/mass of solution) x 100  percent by volume = (volume of solute/volume of solution) x 100  Example: You pack a suitcase that weighs 50 kg. You add 10 kg of t-shirts. What is the percent by mass of t-shirts?  Example: You add 5 mL of acetic acid to 95 mL of water. What is the percent by volume of acetic acid?

Parts per Million  Parts per million is a measure of how many parts of solute are in a million parts of solution.  ppm = (mass solute / total mass of solution) x 10 6  Imagine a jar that has a million jelly beans in it. (Yummie!) If 14 of the jelly beans were yellow we could say that the yellow jelly beans had a concentration of 14 parts per million. Melamine audio ->

Grams per Liter  Grams per liter represents the mass of the solute divided by the volume of the solution.  g/L = grams of solute / liters of solution  Example: You have 20 grams of sodium chloride dissolved in water with a total volume of 5 liters. What is the concentration of NaCl in grams/liter?

Molar Dilutions  Making solutions of lower concentrations from higher concentrations  M 1 V 1 = M 2 V 2  Example: What volume of a 3 M HCl solution is needed to make 2 L of 1 M HCl?  Example: How many liters of 6 M NaOH is required to make 2 L of 4 M NaOH?

Colligative Properties  physical properties affected by the NUMBER of solute particles, NOT the solute identity  vapor pressure lowering  boiling point elevation  freezing point depression  How would dissolving 1 mole of CaCl 2 differ from 1 mole of NaCl in affecting colligative properties? Club soda demo!

solutions have a wider range of P & T where they are in liquid phase