Solutions
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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

Solutions


Solutions1

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

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


Components of solutions

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


Rates of dissolving

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.


Solubility

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


Solubility1

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


Solubility curve

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


Solution concentration

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


Practice problems

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


Dilutions practice problems

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?


Molality

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


Molality examples

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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