Lec' 16 Quantitative Analysis

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Fred J. Grieman
Lec. 16 Quantitative Analysis HW
Problem Set 5
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5 Anions and 5 Reagents 25 possible rxns (4
types NR) Qualitative Analysis Reagents
Typical Reaction HNO3 Acid/Base,
Redox OH- Acid/Base Ba2 Precipitation
Co2 Complexation, Precipitation, Redox (Co3)
H2O2 (H) Redox, Acid/Base H2O2 Good
Reducing and Oxidizing Agent In Acid ? Oxidizing
Agent ½ reactions ______________________________
Oxidizing Agent
_______________________________ Reducing
Agent Can Disproportionate as well in
Acid Solution
Anions
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Solution Stoichiometry ____ ____
Quantitative Analysis
VA nA
mA Precipitation Usually measure mass of
solid to determine mass (e.g.,
CaC2O4) Acid/Base, Redox, Complexation
Usually use _____________ Titration
_____________________________________________
______________________________________
__________ ________ for accurate volume
measurement __________to show end of reaction
Buret filled with titrant
Acid/Base ________ Strong Base with _______
Weak Acid Must know OH- _____________ (with
known Weak Acid) potassium hydrogen phthalate
KHC8H4O4 (____) M 204.2 g/mol ________ used
to make base titrant (very difficult to measure
mass) __________________________________________
at endpoint all HC8H4O4? reacts, small excess OH-
turns indicator pink. Suppose 25.00 mL of (OH-)
to reach endpoint of 0.765 g KHP n(KHP)
_____________ 0.765 g / 204.2 g/mol(KHP) 3.75
x10-3 mol KOH _________ ____________
(3.75x10-3) / 0.02500L) 0.150 M
we can now use to determine Acid amounts
Sample with indicator to show endpoint
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Example Environmental Chemist wants to know
amount of benzoic acid in
effluent in industrial process What mass
? Takes 0.0350 g sample, dissolves it in
water Using buret with ________ NaOH,
neutralizes (end of rxn.) with _________ Net
ionic eq. OH-(aq) C6H5CO2H(aq) ?
H2O(l) C6H5CO2-(aq)
_________ __________ ?
___________ ??? n(OH-) n(C6H5CO2H)
________________ n(OH-) ___________
(0.150 M) (10.60 mL) (1L/1000mL)
1.59 x 10-3
mol ______________ m(C6H5CO2H)
??? ____________________________ (1.59 x 10-3
mol)(122.125 g/mol)
0.194 g Mass ______________________ x 100
0.194 g / 0.350 g x 100 55.5
Structure M 122.125 g/mol
weak acid
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• Balancing Redox Reactions Half Rxn Method
  (__________) (My method below)
• MnO4- C2O42- ? MnO2 CO32-
  in acid
• 1) Assign ox.s ? oxdzd rdcd species
• Write unbalanced ½ rxns. for oxdzd rdcd species
• 
  
• _____________________
  
• 
  
• _____________________
  
• 3) Balance elements except O H
• 4) Add e- to balance ox. change
• 5) Multiply ½ rxns. by factors to balance e-s
• _____________________
  _____
• _________________________________
  _

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Find a rock. Want to know what it is (made of
_________) Redox Titration !!!
- Grind up ______ of rock Via reducing agent
turn all Fe into Fe2 in acid solution Use
________ , a dark purple solution in buret Rxn.
_________________________________________
endpoint solution stays purple 26.00 mL of
titrant to endpoint. ??? m(Fe) ??? Use
_______________________ n(MnO4-)
______________________ (0.02600 L) (0.100)
2.6 x 10-3 mol n(Fe2) ____________________
________ 5 (2.60 x 10-3 mol) 1.30 x 10-2
mol m(Fe) _______________________ (1.30 x
10-2 mol) (55.847 g/mol) 0.726 g Mass(Fe)
____________ x 100 69.8 If rest is O
m(O) 1.04 g 0.726 g 0.314 g n(O)
________ (0.314 g) / 115.9994 g/mol 1.96
x 10-2 mol n(O) / n(Fe) (1.96 x 10-2 mol) /
(1.30 x 10-2 mol) 1.51 ? _____

? _____


_________ Next Time _________________