Mixtures and Solutions
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Mixtures and Solutions Chemistry Matter and Change Chapter 14 Chapter 14 Main Idea Nearly all of the gases, liquids and solids that make up our world are mixtures. Types of Mixtures Chemistry- Matter and Change 14.4 14.1 Main Idea Mixtures can be either heterogeneous or homogeneous. 14.1 Objectives Compare the properties of suspensions, colloids and solutions Identify the types of colloids and types of solutions Describe the electrostatic forces in colloids Predict whether a solution is an electrolyte or nonelectrolyte Test your prediction Review Vocabulary Solute Solvent Molar mass Concentration New Vocabulary Suspension Colloid Brownian motion Tyndall effect Soluble Miscible Insoluble Immiscible Electrolyte Nonelectrolyte Heterogeneous mixtures Mixture- a combination of two or more substances that each retain their individual chemical properties Not the same composition throughout the substance Suspensions Type of heterogeneous mixture Large particles settle if left undisturbed Filter out Colloids Medium sized particles do not settle out, but remain visibly different Cannot filter out Categories of Colloids Particles Solid Liquid Gas Medium Solid Solid sol Solid emulsion or gel Solid foam Liquid Sol Emulsion Foam Gas Solid aerosol Liquid aerosol Examples of Colloids Category Example Dispersed particles Dispersion medium Solid sol Ruby, sapphire Solid Solid Sol Blood, gelatin Solid Liquid Solid emulsion Butter, cheese Liquid Solid Emulsion Milk, mayonnaise Liquid Liquid Solid foam Marshmallow, Dove Gas Solid Foam Whipped cream Gas Liquid Solid aerosol Smoke, dust in air Solid Gas Liquid aerosol Fog, hairspray Liquid Gas Brownian Motion Movement of particles in a colloid Erratic Particles may repel preventing settling Tyndall effect Small particles that do not settle out Too small to be seen unaided Create a visible line when a laser is shined through them (scatter light) Classification of Matter Solutions are homogeneous mixtures Homogeneous mixtures Solvent- material in greater quantity Solute- material in lesser quantity Do not disperse laser light Forming solutions Not all materials will form solutions Soluble- the two substances will form a solution Miscible- two liquids that will form a solution no matter their proportions (tea and water) Insoluble- two materials that never form a solution (sand in water) Immiscible- may be mixed, but will separate quickly (oil and vinegar) Electrolytes vs. Nonelectrolytes The ammeter measures the flow of electrons (current) through the circuit. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter measures a current, and the bulb glows, then the solution conducts. If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting. Definition of Electrolytes and Nonelectrolytes An electrolyte is: A substance whose aqueous solution conducts an electric current. A nonelectrolyte is: A substance whose aqueous solution does not conduct an electric current. Electrolytes? 1. Pure water 2. Tap water 3. Sugar solution 4. Sodium chloride solution 5. Hydrochloric acid solution 6. Lactic acid solution 7. Ethyl alcohol solution 8. Pure sodium chloride ELECTROLYTES: NONELECTROLYTES: Tap water (weak) Pure water NaCl solution Sugar solution HCl solution Ethanol solution Lactate solution (weak) Pure NaCl But why do some compounds conduct electricity in solution while others do not…? Answers to Electrolytes Can you… Compare the properties of suspensions, colloids and solutions Identify the types of colloids and types of solutions Describe the electrostatic forces in colloids Predict whether a solution is an electrolyte or nonelectrolyte Test your prediction Solution Concentration Chemistry- Matter and Change 14.2 14.2 Main Idea Concentration can be expressed in terms of percent or in terms of moles 14.2 Objectives Describe concentration using different units Determine the concentration of solutions Calculate the molarity of a solution Prepare different solutions with given molarity, percent by mass, percent by volume, molality, and mole ratio. Review Vocabulary Solvent Ratio Mass Mole New Vocabulary Concentration Molarity Molality Mole fraction Dilution Concentrated vs. Dilute Expressing Concentration Concentration Description Ratio Percent by mass m assof solute 100 m assof solution Percent by volume volum eof solute 100 m assof solution Molarity m oles of solute liter of solution Molality m oles of solute kg of solution Mole fraction m oles of solute m olesof solute m oles of solution Percent by mass The mass of the solute divided by the mass of the solution In order to maintain a sodium chloride concentration similar to ocean water, an aquarium must contain 3.6 g sodium chloride per 100.0 g of water. What is the percent by mass of NaCl in the solution? Mass of solute: 3.6 g Mass of solution: 100.0 g + 3.6 g =103.6 g Percent by mass = (3.6g/103.6g) x 100 = 3.5% Percent by volume The volume of the solute divided by the volume of the solution What is the percent by volume of ethanol in a solution that contains 35mL of ethanol distributed in 155mL of water? Volume of solute: 35mL Volume of solution: 155mL+35mL = 190mL Percent by volume = (35mL/190mL) x100 = 18% Molarity Most commonly used The moles of solute/liters of solution Represented by M n M V Important Notes Q: What do you call a tooth in a glass of water? A: One molar solution. One way to measure the strength of a solution moles of solute per liter of solution. mole solute M liter solvent Important Notes You must switch all units to moles and liters! Recall 1000 mL = 1 L Important Notes You have 3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that solution? 90.0 g NaCl 1 mol NaCl 3.50 L Solution 58.44 g NaCl = 0.440 M NaCl A 100.5mL intravenous solution contains 5.10g of glucose. What is the molarity of this solution? (The molar mass of glucose is 180.16 g/mol) Moles of solute = 0.0283 mol C6H12O6 5.10 g glucose 1 mol glucose 180.16 g glucose Liters of solution = 100.5 mL 1L = 0.1005 L 1000mL Molarity = 0.0283 mol/0.1005 L = 0.282M Dilution of molar solutions M1V1=M2V2 Important Notes M is molarity; V is volume What volume in milliliters, of a 2.00M calcium chloride stock solution would you use to make 0.50 L of 0.300M calcium chloride solution? M1=2.00M V1=? M2 = 0.300M V2=0.50L V1= 0.50L 0.300M 2.00M V1=75mL = 0.0750L 1000mL 1L Molality Used when volume of solution is highly variable due to temperature differences The moles of solute/kg of solvent Represented by m mol m kg Important Notes Molality The concentration of a solution in moles of solute per kilogram of solvent. n m kg Important Notes You must switch all units to moles and kilograms! Recall 1000 g = 1 kg Important Notes In the lab, a student adds 4.5 g of sodium chloride to 100.0 g of water. Calculate the molality of the solution. Mass of water = 100.0 g = 0.1000 kg Mass of sodium chloride = 4.5g Moles of NaCl 4.5g NaCl 1 mol NaCl 58.44g NaCl = 0.077 mol NaCl Molality =0.077 mol/0.1000 kg = 0.77m Mole fraction Represented by XA and XB and X… Important Notes nA nB XA ; XB nA nB nA nB Mole Fraction 10% 9% 23% 58% A B C D A hydrochloric acid solution contains 36g HCl and 64g H2O. What is the mole fraction for the solution? 36g HCl = 1.0 mol HCl 64g H2O = 3.6 mol H2O XHCl = 0.1mol /4.6 mol = 0.22 XH2O = 3.6 mol/4.6 mol = 0.78 14.2 Can you… Describe concentration using different units Determine the concentration of solutions Calculate the molarity of a solution Prepare different solutions with given molarity, percent by mass, percent by volume, molality, and mole ratio. Factors Affecting Solvation Chemistry- Matter and Change 14.3 14.3 Main Idea Factors such as temperature, pressure and polarity affect the formation of solutions 14.3 Objectives Describe how intermolecular forces affect solvation Define solubility Predict how different factors affect solubility Create solutions that are unsaturated, saturated and supersaturated Review Vocabulary Exothermic Endothermic Solution Polarity Ionic bond Covalent bond Ionization New Vocabulary Solvation Heat of solution Unsaturated solution Saturated solution Supersaturated solution Henry’s law Dissociation The solvation process Like dissolves like Only substances that can become enmeshed in the other substance will dissolve Polar solutes require polar solvents Nonpolar solutes require nonpolar solvents Important Notes Solvation of ionic compounds Charged ends of the polar water molecules get in between the ions in the crystal and force them apart Solvation of molecular compounds Dissolve only when the attractive forces between the molecules of the compound are weaker than the attractive forces between the polar water molecules and the polar solute molecules Water molecules form hydrogen bonds with the polar portions of the solute Heat of solution Energy change during the formation of a solution Some solutions absorb energy during formation while others release energy Factors that affect the rate of solvation Agitation Surface area Temperature Degrees of solubility Solubility of a substance can change with temperature or pressure Saturated A solution that contains the exact amount of solute at a specific temperature and pressure The addition of more solute results in undissolved particles Unsaturated A solution that contains less than the exact amount of solute at a specific temperature and pressure The addition of more solute will result in a greater concentration of the solution Supersaturated A solution that contains more than the exact amount of solute at a specific temperature and pressure Highly unstable Created at a higher temperature or pressure Degrees of saturation UNSATURATED SOLUTION more solute dissolves SATURATED SUPERSATURATED SOLUTION SOLUTION no more solutebecomes unstable, dissolves crystals form concentration Solubility of gases As temperature increases, the solubility of gases decreases As pressure increases, the solubility of gases also increases Henry’s law At a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid S1 S 2 P1 P2 14.3 Can you… Describe how intermolecular forces affect solvation Define solubility Predict how different factors affect solubility Create solutions that are unsaturated, saturated and supersaturated Colligative Properties of Solutions Chemistry- Matter and Change 14.4 14.4 Main Idea Colligative properties depend on the number of solute particles in a solution 14.4 Objectives Describe colligative properties Identify four colligative properties of solutions Determine the boiling point elevation and freezing point depression of a solution 14.4 Review Vocabulary Ion Boiling point Freezing point 14.4 New Vocabulary Colligative property Vapor pressure lowering Boiling point elevation Freezing point depression Osmosis Electrolytes and Colligative Properties Colligative properties depend on the numbers of particles in a solution rather than the identity of the particles Electrolytes Allow electrons to flow Can conduct electricity Vapor Pressure Lowering Reduced number of solvent molecules exposed reduces the vapor pressure above a solution Boiling point elevation Addition of solutes requires more energy to release molecules from a solution, thereby elevating the boiling point. Freezing Point Depression Solute particles interfere with intermolecular bonding, requiring more energy to return to a solid state Equations Freezing point depression Tf K f m Boiling point elevation Tb Kb m Sodium chloride is often used to prevent icy roads and to freeze ice cream. What are the boiling and freezing points of a 0.029m aqueous solution of sodium chloride? Look up on tables Kf (H2O) = 1.86 °C/m Kb (H2O) = 0.512 °C/m Tf = 0.00°C Tb=100°C Given in problem m= 0.029m Tf K f m ΔTf = (1.86 °C/m)(0.029m)=0.11°C Tf =-0.11°C Tb = 100.030°C Osmosis Diffusion of water through a semi-permeable membrane Osmotic pressure Pressure resulting from osmosis 14.4 Can you… Describe colligative properties Identify four colligative properties of solutions Determine the boiling point elevation and freezing point depression of a solution
