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Reactions in Aqueous Solutions II_11

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					Reactions in Aqueous Solutions
       II: Calculations
           Chapter 11
 Calculations Involving Molarity
• Review sections on molarity and percent by mass
  (Chapter 3)
• If 100.0 mL of 1.00 M NaOH solution and 100.0
  mL of 0.500 M H2SO4 solution are mixed, what
  will be the resulting molarity of the salt? Assume
  that the amount of water produced the reaction is
  negligible. What if it’s not? Does anything else
  remain?
   – Volumes are additive
                               mil lim oles of solute
                  Molarity 
                               milliters of solution
 Calculations Involving Molarity
• If 130 mL of 1.00 M KOH and 100 mL of 0.500
  M H2SO4 solutions are mixed, what will be the
  concentration of the products in solution?
   – You need to remember how to determine the limiting reaction. This will
     determine the amount of product formed. From the amount of limiting
     reactant, the amount of excess reactant can be determined.
• In a flask, 1.29 grams of Mg(OH)2 is added to
  50.0 mL of water. This is reacted with 35.0 mL of
  a 1.50 M HCl solution, what will be the
  concentration of the products in the solution?
Note: Write the reactions for the formation of the
  normal salts.
 Calculations Involving Molarity
• What volume of 0.750 M NaOH solution
  would be required to neutralize completely
  100 mL of 0.250 M H3PO4?
  – This is a complete neutralization.
  – What type of reaction is this? What will be the
    products and direction of the arrows?
  There are multiple ways to solve these problems.
  Always start with the balanced equation.
                       Titrations
• Titration - process in which a solution of one reactant, the
  titrant, is carefully added to a solution of another reactant,
  and the volume of titrant required for complete reaction is
  measured.
• Equivalence point – The point at which stoichiometrically
  equivalent amounts of an acid and base have reacted.
• Indicator – A compound that exhibits its different colors in
  solutions of different acidities. Used to determine the
  point at which an acid-base reaction is complete.
• End point – The point at which an indicator changes color
  and a titration is stopped. The end point should coincide
  with the equivalence point.
DEMO: Titration with an indicator. Use the numbers for a
  future problem.
                   Titrations
• What is the molarity of a freshly-made HCl
  solution if 36.7 mL of the HCl solution is
  neutralized with 28.2 mL of 0.355 M NaOH
  solution?
• Previous titration.
• What is the molarity of a calcium hydroxide
  solution if 41.9 mL of the solution is neutralized
  with 19.1 mL of 0.418 M HCl solution?
                       Titrations
• Standard solutions – solutions of accurately known
  concentrations.
   – Primary standard – A substance of a known high degree
     of purity that undergoes one invariable reaction with the
     other reactant.
      • Look at page 408 for the properties of a primary standard
   – Secondary standard – A solution that has been titrated
     against a primary standard.
• Standardization – The process by which the
  concentration of a solution is accurately determined
  by titrating with a primary standard.
    Using Primary Standards for
             Titrations
• A commonly primary standard for solutions of
  acids is Na2CO3. Even though this is a ____ salt,
  it reacts with acids.
   – H2SO4 + Na2CO3  Na2SO4 + CO2 + H2O
      • How does the reaction produce CO2 and H2O?
   – Calculate the molarity of a sulfuric acid solution if 23.2
     mL of it reacts with 0.212 g of Na2CO3.
   – Calculate the molarity of a HCl solution if 28.5 mL of it
     reacts with 0.458 grams of Na2CO3.
    Using Primary Standards for
             Titrations
• A common primary standard for solutions of bases
  is the acidic salt, potassium hydrogen phthalate,
  KC6H4(COO)(COOH) or KHP.
   – This acidic salt is obtained by reacting phthalic acid
     with KOH (see page 409). One hydrogen remains to
     neutralize bases.
   – The salt is highly soluble and can be obtained in a high
     state of purity.
   – Molecular weight is ____
    Using Primary Standards for
             Titrations
• Calculate the molarity of a NaOH solution if 27.3
  mL of it reacts with 0.4084 g of KHP.
• What if Sr(OH)2 reacts with KHP? Write the
  balanced equation.
• An impure sample of oxalic acid, (COOH)2, had a
  mass of 0.1743 g. It was dissolved in water and
  titrated with 39.82 mL of 0.08915 M NaOH
  solution. Calculate the percent purity of the
  (COOH)2 sample.
   Equivalent Weights and Normality
• Normality is the number of equivalent
  weights of solute per liter of solution.
              number of equivalent weights of solute no. eq no. meq
Normality                                                
                        liter of solution              L      mL

• Equivalent weight of an acid is the mass in
  grams necessary to furnish NA of H+ ions.
    – Monoprotic (HCl) 1 mol = 1 eq
    – Diprotic (H2SO4) 1 mol = 2 eq
    – Triprotic (H3PO4) 1 mole = 3 eq
 Equivalent Weights and Normality
• Works the same way for bases
  – NaOH, Ca(OH)2, and Al(OH)3
• Table 11-1 in textbooks
  – What is the mass of one equivalent of H2SO4?
  – What is the mass of one equivalent of Al(OH)3?
• Calculate the normality of a solution that
  contains 196 g of sulfuric acid in 1500 mL
  of solution.
 Equivalent Weights and Normality

• Calculate the molarity and normality of a
  solution that contains 34.2 g of barium
  hydroxide in 8.00 liters of solution.
• One equivalent of an acid reacts with one
  equivalent of a base. It follows that for an
  acid-base reaction that goes to completion.
  Number of equivalents of acid = Number of equivalents of base
 Equivalent Weights and Normality

• The product of the volume and its normality
  is equal to the number of equivalents of
  solute contained in the solution.
                                    eq acid
       L acid  N acid    L acid           eq acid
                                     L acid
  – This relationship also works for a base.
• What volume of 6.0 M phosphoric acid
  solution is required to prepare 900 mL of
  0.200 N phosphoric acid solution?
 Equivalent Weights and Normality

• What is the normality of a sulfuric acid
  solution if 31.3 mL of it reacts with 0.318 g
  of sodium carbonate?
• 30.0 mL of 0.750 N nitric acid solution
  required 22.5 mL of calcium hydroxide
  solution for neutralization. Calculate the
  normality and the molarity of the calcium
  hydroxide solution.

				
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