The
Breathalyzer
The
Breathalyzer
The Breathalyzer Reaction
C2H5OH
H2O
Ethanol
+
Cr2O72- + H+ →
Orange
Acid
CH3COOH
Acetic Acid
+ Cr3+ +
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
Legal Limit New Driver
0.08 mg/mL
0.00 mg/mL
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.
0.000 %
0.05 %
0.10 %
0.15 %
0.20 %
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
FB
IC
SO42D
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 +
0.00675 L
0.0250L
0.100 M
?M
0.00675 L MnO4- x
[Fe2+]
=
0.100 mole x
1L
0.0250 L
=
0.135 M
5Fe3+
5 moles Fe2+
1 mole MnO4-
Write the anode and cathode reactions.
voltmeter
NaNO3aq)
Pt
Pt
Inert electrodes- look at the solution for the reactions
MnO4- in acid
H2O2(aq)
Cathode
Anode
Cathode:
MnO4- + 8H+ + 5e-
Anode:
H2O2
→
→
O2 + 2H+ +
What happens to the mass of the cathode?
Constant
What happens to the mass of the anode?
Constant
What happens to the pH of the cathode?
Increases
What happens to the pH of the anode?
Decreases
Mn2+ + 4H2O
2e-
Non-Inert Electrodes
The Cathode will stay inert
A non-inert Anode might oxidize
DC Power
Cu
Cathode
Reduction
2H2O + 2e-→H2 +2OH-0.41 v
-
+
K+
SO42H2O
K2SO4(aq)
Cu might oxidize
Cu
You must look at the
possible oxidation of:
SO42H2O
Cu
Strongest Reducing Agent
Non-Inert Electrodes
The Cathode will stay inert
A non-inert Anode might oxidize
DC Power
Cu
Cathode
Reduction
2H2O + 2e-→H2 +2OH-0.41 v
+
Cu
K+
SO4
Cu might oxidize
2-
H2O
K2SO4(aq)
+
Anode
Oxidation
Cu(s) → Cu2+ + 2e-0.34 v
Review of Cells
Electrochemical
Electrolytic
Is a power supply
Spontaneous (+)
Makes electricity
Requires power supply
Nonspontaneous (-)
Makes chemicals
Reduction is highest on Chart
Reduction is the –ve
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:
Zn
Reaction: Zn(s) → Zn2+ + 2e-
0.76 v
Cathode:
Cu
Reaction: Cu2+ + 2e- → Cu(s)
0.34 v
E0
1.10 v
=
Higher on reduction Chart
Electrolytic Cell: Molten AlCl3
Al3+
Cl-
Anode:
C
Reaction:
2Cl- → Cl2(g) + 2e-
-1.36 v
Cathode:
C
Reaction:
Al3+ + 3e- → Al(s)
-1.66 v
E0
-3.02 v
=
MTV =
+3.02 v
The anode and cathode are inert C or Pt
Vowels:
Consonants:
Anode
Cathode
Anion
Cation
Oxidation
Reduction
Electrolytic Cell: KBr(aq)
Anode:
C
Cathode:
C
Anode
Oxidation
K+
Br-
Anion or Water
H2O
Oxidation of water
K+
Electrolytic Cell: KBr(aq)
Br-
2Br- → Br2(g) + 2e-
Anode:
C
Cathode:
C
Anode
Oxidation
Anion or Water
Cathode
Reduction
Cation or water
H2O
-1.09 v
K+
Electrolytic Cell: KBr(aq)
Br-
H2O
Anode:
C
2Br- → Br2(g) + 2e-
-1.09 v
Cathode:
C
2H2O + 2e- → H2(g) + 2OH-
-0.41 v
E0
-1.50 v
=
MTV =
+1.50 v
Anode
Oxidation
Anion or Water
Cathode
Reduction
Cation or water
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