The Breathalyzer
The Breathalyzer
The Breathalyzer Reaction
C2H5OH + Cr2O72- + H+ → CH3COOH + Cr3+ +
H2OEthanol Orange Acid Acetic Acid Green Water If the orange colour decreases there is alcohol present. It is measured with a spectrophotometer. The more it decreases, the higher the blood alcohol content. Legal Limit Class 5 Licence 0.08 mg/mLLegal Limit New Driver 0.00 mg/mL
0.000 % 0.05 % 0.10 % 0.15 % 0.20 %
Test tubes each contain 5 mL 0.25 M K2Cr2O7 + 5 mL of 6.0 M H2SO4 + 1 drop of 0.10 M AgNO3 (catalyst) and 0, 1, 2, 3, 4, drops respectively of 10.0 % ethanol.
Redox Titrations A redox titration is the same as an acid-base titration except it involves a redox reaction. Reagents are chosen so that the reaction is spontaneous.
Pick a suitable reagent for redox titration involving IO3- in acid
solution.A F-
B I-
C SO42-
D Cl-
Pick the spontaneous reaction
6.75 mL of 0.100 M KMnO4 is required to titrate 25.0 mL of FeCl2.
Calculate the [Fe2+].
MnO4- + 8H+ + 5Fe2+ → Mn2+ + 4H2O + 5Fe3+
0.00675 L 0.0250L0.100 M ? M
[Fe2+] =
0.00675 L MnO4- x 0.100 mole
1 L
x 5 moles Fe2+
1 mole MnO4-
0.0250 L
= 0.135 M
Write the anode and cathode reactions.
Pt Pt
H2O2(aq)MnO4- in acid
NaNO3aq)
voltmeter
Inert electrodes- look at the solution for the reactions
Cathode
Anode
Cathode: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O
Anode: H2O2 → O2 + 2H+ + 2e-
What happens to the mass of the cathode?ConstantWhat happens to the mass of the anode?ConstantWhat happens to the pH of the cathode?IncreasesWhat happens to the pH of the anode?Decreases
-CathodeReduction2H2O + 2e-→H2 +2OH-
-0.41 v
Non-Inert Electrodes
DC Power
- +
K2SO4(aq)
Cu
Cu might oxidize
K+
SO42-
H2O
Cu
The Cathode will stay inert A non-inert Anode might oxidize
You must look at the possible oxidation of:
SO42-
H2O Cu
Strongest Reducing Agent
-CathodeReduction2H2O + 2e-→H2 +2OH-
-0.41 v
Non-Inert Electrodes
DC Power
- +
K2SO4(aq)
Cu
Cu might oxidize
K+
SO42-
H2O
Cu
The Cathode will stay inert A non-inert Anode might oxidize
+AnodeOxidationCu(s) → Cu2+ + 2e-
-0.34 v
Review of Cells
Electrochemical Electrolytic Is a power supply Requires power supplySpontaneous (+) Nonspontaneous (-)Makes electricity Makes chemicals
Reduction is the –ve Reduction is highest on Chart
For all cells:
Cations migrate to the cathode, which is the site of reduction. Anions migrate to the anode, which is the site of oxidation. Electrons travel through the wire from anode to cathode.
Complete the Chart Electrochemical Cell: Zn, Zn(NO3)2 II Cu, CuSO4
Anode: Reaction:
Cathode: Reaction:
E0 = Higher on reduction Chart
Zn
Cu
0.76 vZn(s) → Zn2+ + 2e-
Cu2+ + 2e- → Cu(s) 0.34 v
1.10 v
Electrolytic Cell: Molten AlCl3
Anode: Reaction: Cathode: Reaction:
Consonants: Cathode Cation ReductionVowels: Anode Anion Oxidation
The anode and cathode are inert C or Pt
C
C
2Cl- → Cl2(g) + 2e- -1.36 v
Al3+ + 3e- → Al(s) -1.66 v
E0 = -3.02 v MTV = +3.02 v
Al3+ Cl-
Electrolytic Cell: KBr(aq) K+ Br- H2O
Anode: Cathode:
Anode Oxidation Anion or Water
C
C
Oxidation of water
Electrolytic Cell: KBr(aq) K+ Br- H2O
Anode: 2Br- → Br2(g) + 2e- -1.09 v
Cathode:
Anode Oxidation Anion or Water
C
C
Cathode Reduction Cation or water
Electrolytic Cell: KBr(aq) K+ Br- H2O
Anode: 2Br- → Br2(g) + 2e- -1.09 v
Cathode: 2H2O + 2e- → H2(g) + 2OH- -0.41 v
Anode Oxidation Anion or Water
C
C
Cathode Reduction Cation or water
E0 = -1.50 v MTV = +1.50 v
Is Al a reactive or non-reactive metal?
Look on page 8
Reactive as Al is a relatively strong reducing agent.
Why is Al used for boats, patio furniture, swing sets, and trucks boxes?
Al makes a clear transparent Al2O3 paint like coating that prevents further oxidation.
How to Fail a Breathalyzer Video 1
Breathalyzer Video 2
Drunks
Jeff Dunham