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									CHAPTER 15


 Solutions
Solute
A solute is the dissolved substance in a
solution.
   Salt in salt water     Sugar in soda drinks
         Carbon dioxide in soda drinks
Solvent
A solvent is the dissolving medium in a
solution.
   Water in salt water     Water in soda
Concentrated vs. Dilute
     Saturation of Solutions
 A solution that contains the maximum amount of
  solute that may be dissolved under existing
  conditions is saturated.

 A solution that contains less solute than a
  saturated solution under existing conditions is
  unsaturated.

 A solution that contains more dissolved solute
  than a saturated solution under the same
  conditions is supersaturated.
Saturation and Equilibrium
Solubility Rules

 Reference Tables
          Solubility Values
• Solubility of a substance is the amount of
  that substance required to form a
  saturated solution with a specific amount
  of solvent at a specified temperature

• The rate at which a substance dissolves
  does not alter the substances solubility
 Factors that Affect Solubility
• Temperature

  – Solubility of solids increases with temperature

  – Solubility of gases decreases with temperature


• Pressure

  – has no real effect on the solubility of liquids and solids in liquid
    solvents

  – Increasing pressure increases the solubility of gases in liquids
         Solubility Curves
• Each line represents a solute

• Higher curves mean that the solute is
  more soluble, lower curves are less
  soluble

• ABOVE the curve is SUPERsaturated,
  on the curve is saturated, and UNDER
  the curve is UNsaturated
Solubility Chart
          Solubility Trends
 The solubility of MOST solids increases
  with temperature.

 The rate at which solids dissolve
  increases with increasing surface area of
  the solid.

 The solubility of gases decreases with
  increases in temperature.

 The solubility of gases increases with
  the pressure above the solution.
Therefore…
Solids tend to dissolve best when:
      o Heated
      o Stirred
      o Ground into small particles

Gases tend to dissolve best when:
      o The solution is cold
      o Pressure is high
Review Questions
              Problem 18
     A physical change occurs when

– A a peach spoils


– B a bracelet turns your wrist green


– C a copper bowl tarnishes


– D a glue gun melts a glue stick
                 Problem 19
What substance has a melting point of -94°C
        and a boiling point of 65°C?

 – a. Ethanol

 – b. Chlorine

 – c. Hexane

 – d. Methanol
                 Problem 20
22.4 liters of a gas has a mass of 36.5 grams.
          What is the identity of the gas?

 – a. Chlorine

 – b. Hydrogen chloride

 – c. Nitrogen

 – d. Hydrogen
Day 2
Molarity and Dilutions
           Heat of Solution
The Heat of Solution is the amount of heat
energy absorbed (endothermic) or released
(exothermic) when a specific amount of
solute dissolves in a solvent.



  •Endothermic: absorbs heat so it feels cool

  •Exothermic: releases heat so it feels hot
               Molarity
The concentration of a solution
measured in moles of solute per liter of
solution.

         mol of solute = M
         L of solution
              Example
What is the molarity of 2.5 mol KCl in 1.0L
                 solution?

                 M= mol
                     L

                M= 2.5mol
                     1L

                 M= 2.5M
             Example 2
What is the molarity of 0.96g MgCl2 in 500mL of
                    solution?

                    M= mol
                       L

    0.96g MgCl2 1mol MgCl2 = .01 mol MgCl2
                 95g MgCl2

               M= .01 mol MgCl2
                    .500L

                   M= .02M
              Example
How many moles of solute are contained in
   15.25mL of a 2.1M solution of CaCl2?

                M = mol
                     L

     # of mol = molarity x L of solution

         # of mol = 2.1M (.01525L)

        # of mol = .032 mol CaCl2
Practice Problems
        Practice 1
What is the molarity of 1.35 mol
  H2SO4 in 245mL solution?


           M= 5.51M
         Practice 2

What is the molarity 9.33g Na2S in 450
             mL solution?


              M= 0.27M
      Practice 3
 How many moles of solute are
contained in 125mL of a 0.050M
      solution of Ba(OH)2?


         .00625mol
        Practice 4

  How many grams of solute are
contained in 64.3mL of a 0.0238M
        solution of KOH?


            .0859g
          Practice 5
   How many grams of solute are
contained in 142mL of a 1.4M solution
              of K2SO4?


               34.6g
                          Dilutions
• Because the # of moles of solute does not change
  during a dilution

   Moles of solute in the stock solution = moles of solute after dilution


                             M1V1=M2V2

M1V1 is the molarity and volume of the stock solution
  and M2V2 is the molarity and volume of the diluted
                        solution
                    Example
• How many milliliters of 2.55M NaOH is needed to make
  125ml 0.75M NaOH?

                     M1V1 = M2V2

                       V1= M2V2
                           M1

                     V1=(.75)(125)
                           2.55

                      V1= 36.76L
Practice Problems
         Practice 1
How would you prepare 500mL of 3 M
     HCl using 6 M HCl from the
             stockroom?


             250mL
         Practice 2
How much 12 M HCl must be used to
     prepare 500 ml of a 1 M HCl
              solution?


            41.67mL
       Homework

Molarity and Dilution Problems
Review Questions
                Problem 21
• Which of the following substances best
  illustrates polar covalent bonding?

  – a. HCl

  – b. NaBr

  – c. CsF

  – d. Cl2
                  Problem 22
• The methane, CH4, gas molecule exhibits what
  type of geometric shape?

  – a. trigonal planar

  – b. tetrahedral

  – c. bent or V-shaped

  – d. trigonal pyramidal
               Problem 23
• Which substance would have London
  dispersion forces as the main type of
  intermolecular forces of attraction?

  – a. H2O

  – b. F2

  – c. HCl

  – d. NaCl
               Problem 24
• Which of the following compounds is an
  exception to the octet rule?

  – a.BH3

  – b.CH4

  – c.NH3

  – d.H2O

								
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