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Solutions

Solutions. Solutions. Definition: Homogeneous mixture of two or more substances in a single phase. Like Dissolves Like (i.e. nonpolar molecules dissolve in nonpolar molecules) Solid mixtures: alloys (brass, sterling silver) Liquid mixtures: alcohol & water Gas mixtures: air. Other Terms.

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Solutions

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  1. Solutions

  2. Solutions • Definition: Homogeneous mixture of two or more substances in a single phase. • Like Dissolves Like (i.e. nonpolar molecules dissolve in nonpolar molecules) • Solid mixtures: alloys (brass, sterling silver) • Liquid mixtures: alcohol & water • Gas mixtures: air

  3. Other Terms • Soluble: capable of dissolving • Insoluble: incapable of dissolving • Miscible: 2 liquids dissolve into each other • Immiscible: 2 liquids do not dissolve into each other • Solubility: how much of a given solute a certain solvent can dissolve at a certain temperature & pressure

  4. Components of Solutions • Solute: is dissolved by the solvent. • Found in lesser quantities • May be electrolytes (conduct electricity) or non-electrolytes (does not conduct electricity) • Solvent: does the dissolving • Water is the universal solvent • http://www.dlt.ncssm.edu/TIGER/chem2.htm#stoich

  5. Rates of Dissolving Rate of dissolving may speed up due to the following: • Increased Surface Area: breaking the solute up into smaller pieces • Increased Stirring: increases particle collisions • Heating: particles move faster = more collisions.

  6. Solubility • Varies with temperature • Solids & Liquids: Temp ↑, solubility ↑ • Gases: Temp ↑, solubility ↓ • Henry’s Law: Solubility of a gas in liquid is directly proportional to pressure

  7. Solubility • Saturated: The maximum amount of a solute that can be dissolved into a solvent. • Unsaturated: less than the maximum amount of solute that can be dissolved. • Supersaturated: More dissolved solute than a saturated solution at the same temperature • Must be heated, then cooled slowly • Very unstable

  8. Solubility Curve • The lines represent the different saturation points for different compounds • Notice, the solubilities are measured in g/100 g H2O • Under the line is unsaturated, over the line is supersaturated

  9. Solution Concentration • The concentration of a solution is measured in Molarity (M) • M = moles / liter • M = mol/L • (moles of solute per liters of solution) • Diluting solutions: • M1V1 = M2V2

  10. Practice Problems • You have 3.50 L of solution that contains 90.0 g of NaCl. What is the molarity of this solution? Answer: 0.44 M • You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl are present? • Answer: 0.4 mol HCl • What volume of 3.00 M NaCl is needed for a reaction that requires 146.3 g of NaCl? • Answer: 0.834 L

  11. Dilutions Practice Problems • You want to make 2.3 L of a 3.5 M H2SO4 solution. If you only have 12 M sulfuric acid in stock, how much must be added to water to make the solution you need? • Answer: • In lab you produce 2.5 L of 6 M HNO3. If you added 0.5 L of a concentrated solution to get this solution, what was the original concentration of the acid?

  12. Molality: • Another way to measure concentration. • Moles of solute per kilogram of solvent m = mol / kg • Notice: solvent must be in kg! • Example: A solution was prepared by dissolving 17.1 g of sucrose (C12H22O11) in 125 g of water. Find the molal concentration. • Answer: 0.400 m

  13. Molality Examples • A solution of I2 in CCl4 is used when iodine is needed for certain chemical tests. How much iodine must be aded to prepare a 0.480 m solution of iodine in CCl4 if 100.0 g of CCl4 is used? • Answer: 12.2 g of I2 • What is the molality of a solution composed of 255 g (CH3)2CO dissolved in 200. g of water? • Answer: 22 m

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