Presentation on theme: "Solutions & Concentration. Water Polar molecule w/ polar bonds Causes surface tension & ability to dissolve polar molecules and ionic compounds."— Presentation transcript:
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