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Mixtures and Solutions

Mixtures and Solutions. Types of mixtures. Heterogeneous mixture: Heterogeneous mixtures do not blend smoothly. Individual substances can still be seen Suspension: A suspension is a heterogeneous mixture where particles will settle to the bottom if left undisturbed. Example: sand in water.

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Mixtures and Solutions

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  1. Mixtures and Solutions

  2. Types of mixtures • Heterogeneous mixture: • Heterogeneous mixtures do not blend smoothly. Individual substances can still be seen • Suspension: • A suspension is a heterogeneous mixture where particles will settle to the bottom if left undisturbed. • Example: sand in water. • Colloids: • Colloids are heterogeneous mixtures where particles will not settle to the bottom. • Example: Milk

  3. Homogeneous Mixtures • Homogeneous mixtures are mixtures where a substance is dissolved in another substance. These are also called solutions. • Parts of a solution: • Solute: The substance that is dissolved • Solvent: The substance that does the dissolving • When a solute readily dissolves in a solvent it is said to be soluble. • Two liquids that can be combined to make a solution are said to be miscible.

  4. A solute that does not readily dissolve in a solvent is said to be insoluble. • Two liquids that do no mix to form a new solution are said to be immiscible.

  5. Solution Concentration • Concentration is the measure of how much solute is dissolved in the solution. • There are many ways to measure concentration • Percent by mass: • (Mass of solute/Mass of solution) x 100 • Percent by volume: • (Volume of solute/Volume of solution) x 100 • Molarity: • Moles of solute/Liter of solution • Molality: • Moles of solute/Kilograms of solvent • Mole Fraction: • Moles of solute/Moles of solute + Moles of solvent

  6. Percent by mass • In order to maintain a sodium chloride concentration similar to ocean water, an aquarium must contain 3.6g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution? • 3.5% • What is the percent by mass of NaHCO3 in a solution containing 20.0 g of NaHCO3 dissolved in 600.0 mL of H2O? • 3%

  7. Percent by Volume • What is the percent by volume of ethanol in a solution that contains 35mL of ethanol dissolved in 155mL of water? • 18%

  8. Molarity • A 100.5 mL intravenous solution contains 5.10 g of glucose. What is the molarity of the solution? The molar mass of glucoes is 180.6 g/mol • 0.282M

  9. If you have 1500 g of a bleach solution with a percent by mass of NaOCl of 3.62 % how many grams of NaCOl are in the solution? • 54.3 g • What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL of isopropyl alcohol in 1.1 L of water? • 2.1 % • Calculate the molarity of 1.6 L of a solution containing 1.55 g of KBr. • 8.13 x 10-3

  10. Molality • In the lab a student adds 4.5 g of NaCl to 100.0 g of water. Calculate the molaity of the solution. • 0.77 mol/kg

  11. Preparing Solutions • How would you prepare 1 L of a 1.5 molar CuSO4 Solution? • Diluting Solutions: • Dilution equation M1V1 = M2V2 • Calculate the new volume if you wanted to dilute the above solution to 0.5 molar.

  12. Diluting Solutions • Remember • Molarity = (Moles of solute/Liters of solvent) • The Dilution Equation: • M1V1 = M2V2 • Example: • What volume of a 2.00M CaCl2 solution would you use to make 0.50 L of a 0.300M solution? • M1 = 2.00M • V1 = ? • M2 = 0.300M • V2 = 0.5L • (2.00M)(V1) = (0.300M)(0.5L) • V1 = 0.075 L

  13. What volume of a 3.00M KI solution would you use to make 0.300 L of a 1.25M KI solution? • 125mL • How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100.0mL of 0.25M H2SO4? • 5.0mL

  14. Mole Fraction • To express concentration as a mole fraction we need to know the number of moles of solute and the number of moles of solvent. • The mole fraction is calculated by dividing the number of moles of either the solute or solvent by the total number of moles in the solution.

  15. Example • If we have a solution that contains 36 g of HCl and 64 g of H2O. What are the mole fractions of HCl and H2O? • HCl: • H2O:

  16. Practice • What is the mole fraction of NaOH in an aqueous solution that contains 22.8% NaOH by mass? • If the mole fraction of H2SO4 is an aqueous solution is 0.325, what is the percent by mass of H2SO4

  17. Factors Affecting Solvation • Many physical factors affect the solubility of a solute. • Such as: • Temperature • Pressure • Polarity • Solvation is the process of surrounding solute particles with solvent particles.

  18. Aqueous ionic solutions • Many ionic compounds are soluble in water. Why? • Water is a polar molecule. • Why might an ionic compound not be water soluble?

  19. Heat of solution • The overall energy change that occurs during the formation of a solution is called the heat of solution. • certain solvation processes are exothermic while others are endothermic.

  20. Factors that affect solvation • Agitation: • Stirring or shaking moves solvated particles away from the surface of the solid and allows more solute particles to move into solution. • Surface Area: • Breaking the solute into small pieces increases the available surface area and increase the rate of solvation. • Temperature: • As temperature increase so does the rate of solvation.

  21. Types of solutions • Unsaturated: • A solution that more solute could be dissolved in. • Saturated: • In a saturated solution the rate of solvation and the rate of crystallization are in equilibrium. • Supersaturated solution: • A super saturated solution is a solution that has more solute dissolved in it that it would normally allow.

  22. Solubility of Gases • Unlike solid solutes the solubility of gases (CO2, or O2 for example) increases as the temperature of the solvent goes down. • The solubility of gases is also affected by pressure. How? • Think about soda.

  23. Henry’s Law • Henry’s Law states that at a constant temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. • Henry’s Law • S1/P1 = S2/P2 • Example: • If 0.85g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25o C, how much will dissolve in 1.0 L at 1.0 atm at the same temperature? • 0.21 g

  24. Decompression Sickness • Decompression sickness is a term used to describe the effects of a drop in external pressure on a persons body. • One common symptom of decompression sickness is AGE, Arterial Gas Embolism. • The bubbles that form in the blood stream from gas leaving solution can restrict blood flow.

  25. Boiling Point Elevation • Dissolving a solute in a solution raises the boiling point of the solution. • This is called boiling point elevation. • We can calculate the difference in boiling point (Δ Tb) by multiplying a solutions molality by a constant we look up for our particular solvent (Kb). • Δ Tb = Kbm

  26. What is the boiling point of a 0.625m aqueous solution of a nonelectrolyte?

  27. What is the boiling point of a 0.4m aqueous solution of Ca(OH)2 (A strong electrolyte) Kb = 0.512 oC/m

  28. Molal Boiling Point Elevation Constants.

  29. Freezing Point Depression • Adding a solute to a solvent also lowers the solvents freezing point. • The equation is very similar to boiling point elevation. • ΔTf = Kfm

  30. Example • Sodium chloride is often used to prevent icy roads and to freeze ice cream. What are the boiling point and freezing point of a 0.029m AQUEOUS solution of sodium chloride? • BP: 100.03 0C • FP: -0.11 oC

  31. Calculate the freezing and boiling point of a solution containing 6.42 g of sucrose (a nonelectrolyte) in 100.0 g of water. • Tf = -0.350 oC • Tb = 100.096 oC • Calculate the freezing and boiling point of a solution containing 23.7 g of Copper (II) sulfate (A strong electrolyte) in 250 g of water • Tf = -2.02 oC • Tb = 100.606 oC • Calculate the freezing and boiling point of a solution containing 0.15 moles of the compound naphthalene, a nonelectrolyte in 175 g of benzene (Normal F.P. = 5.5, Normal B.P. = 80.1, Kf = 5.12, Kb = 2.53) • Tf = 1.1 oC • Tb = 82.3 oC

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