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