General Chemistry Review

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Lecture 7

• General Chemistry Review

2
Section 5.1

• Using the symbols for the quantities, we have
• n m/(f wt) or m n x f wt or f wt m/n
• Using the symbols for the units, we have
• mol g/(g/mol) or g mol x g/mol or g/mol
  g/mol
• Can insert milli-, work with mg, mmol, etc.
• mg mmol x mg/mmol or mg mmol x g/mol, for
  example

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Section 5.2

• Using the symbols for the quantities, we have
• C n/V or n C x V or V n/C
• Using the symbols for the units, we have
• M mol/L or mol M x L or L mol/M
• Where molarity, M, has units of mol/L
• Can insert milli- as before
• M mmol/mL or mmol M x mL, etc.
• I personally prefer learning a relationship and
  using algebra as opposed to dimensional analysis,
  but both of them work fine

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Other Concentration Terms

• Normality (N) See Section 5.6
• Formality (F) Not used much now
• Same as analytical concentration
• Molality (m) We wont need
• Analytical concentration (well use C x)
• What you put in the bottle
• Put 1 mol MgCl2 in 1 L solution, analytical
  concentration is 1 M MgCl2
• Equilibrium concentration (well use X)
• What it turns into
• MgCl2 0 M, Mg2 1 M, Cl- 2 M

5
Density of Solutions

• Volume changes with temperature, density changes,
  concentrations change (except molality)
• Now is a good time to look at Example 2.4 and the
  effect of T on concentration
• Relate by mass, molarity, and density
• M x D x 1000/f wt of solute
• Can you make the units work out?

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Dilutions

• C x V (conc.) C x V (dilute)
• or M x L (conc.) M x L (dilute)
• Use mL both sides to make it even easier
• Ill ask for questions on Examples 5.9 through
  5.13
• If there are none, well move on
• Dilutions are covered in Ch. 3 of the Whitten
  Chem 105 text

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Section 5.3

• Ways to express analytical results
• by mass
• Can use any mass or weight units
• For trace amounts (on a weight/weight basis)
• ppt mg/g g/kg
• ppm µg/g mg/kg
• ppb ng/g µg/kg
• ppt also can mean parts per trillion these days
• When using ppt, clarify which one you mean
• 0.0002 0.002 ppt 2 ppm 2,000 ppb
• Know these relationships

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More Concentration Terms

• Weight/volume basis
• Common in medicinal and clinical chemistry
• 5 glucose IV 5 g glucose/100 mL solution
• At trace levels in water solution, mg/L mg/kg
  since 1 L of water has a mass of 1 kg
• 2 mg/L ? ppm ? ppb
• Volume/volume basis
• Rarely used except for miscible liquids like
  alcohol and water (100 proof 50 (v/v))

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Section 5.4

• Titrations
• Can be highly accurate, but a bit tedious
• Typically the analyte is in the flask, the
  titrant is in the buret
• Titrant is a standard solution (known M)
• Prepared directly from a primary standard or
• Standardized against a primary standard
• Whats a primary standard?
• Reaction should be stoichiometric, rapid,
  quantitative, specific
• Visual indicator color change (the end point)
  should be close to the equivalence point

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Types of Volumetric Methods

• Acid-Base
• Experiment3
• Precipitation
• Experiment 2
• Complexometric
• We wont do one of these this year
• Redox
• Experiment 4

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Section 5.5

• Lots of practice in Chem 105 stoichiometry!
• Ill ask for questions on Examples 5.18 through
  5.29 (but omit Example 5.27)
• Some errors and clarification
• 5.19 0.1288 M hydrochloric acid
• 5.24 2 equations just above this example are
  missing the mL term
• 5.24 EDTA H2Y2- in this example
• 5.28 Now EDTA is H4Y

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Section 5.6

• We probably wont have time to cover this section
• The concept of equivalents is not typically
  taught these days
• But is still used in commercial analytical labs
  and in medicine
• What follows can be a reference for you if we
  dont have time to cover it

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The Equivalents/Mole Factor

• For acid-base reactions, look at H and OH-
• HCl and NaOH have 1 eq/mol
• H2SO4 and Ba(OH)2 have 2 eq/mol
• H3PO4 and Al(OH)3 have 3 eq/mol
• For redox reactions, look at electrons or change
  in oxidation number
• Fe3 to Fe2 has 1 eq/mol
• Fe3 to Fe has 3 eq/mol
• MnO4- to Mn2 has 5 eq/mol
• For other situations, look at charge
• Na has 1 eq/mol
• Mg2 has 2 eq/mol

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Normality (Equivalents/Liter)

• Molarity x eq/mol Normality (N)
• 1 M HCl is 1 N, 1 M NaOH is 1 N
• 1 M H2SO4 is 2 N
• 1 M KMnO4 is 5 N (when Mn2 is product)
• 1 M Ca2 2 N
• For any reaction, regardless of the balanced
  equation, N x L N x L
• No mole ratio is needed

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Equivalent Weights (g/eq)

• Eq wt f wt/(eq/mol)
• Eq wt of NaOH is (40 g/mol)/(1 eq/mol) 40 g/eq
• Eq wt of H2SO4 (98 g/mol)/(2 eq/mol) 49 g/eq
• Guess what? 40 g of NaOH reacts with 49 g of
  H2SO4! Their weights are equivalent get it?
• Historically, equivalent weights were used before
  chemists knew the formulas for compounds
• They figured out that, for example, that 26 g of
  aluminum hydroxide reacted with 36.5 g of HCl,
  and called those weights equivalent

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Equivalents in Medicine

• Still commonly used to describe electrolyte
  balance in body fluids
• Total charge from cations must equal total charge
  from anions
• Concentrations of Na, Ca2, etc. often expressed
  as mEq/dL (milliequivalents per deciliter)
• Total mEq/dL cations total mEq/dL anions

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Section 5.7 and 5.8

• Titer g analyte/mL titrant
• Just a stoichiometric shortcut
• Makes repetitive calculations faster
• Gravimetric factor
• Weve already seen this in Ch. 10
• Another stoichiometric shortcut
• Makes repetitive calculations faster
• Can use plain old Chem 105 stoichiometry for both
  and not worry about them

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Lecture 8 Assignment

• Read Section 11.4, Sections 8.2 and 8.3, Sections
  2.5 and 2.6, Section 12.1, and Sections 14.4
  through 14.8
• Sorry to have you hopping around so much, but I
  must give you the background for several upcoming
  experiments