The Breathalyzer

The Breathalyzer

The Breathalyzer Reaction C2H5OH + Cr2O72- + H+ → CH3COOH + Cr3+ + H2O Ethanol 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/mL Legal Limit New Driver 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 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 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 0.0250L 0.100 M ? M 0.00675 L MnO4- x 0.100 mole 1 L x 5 moles Fe2+ 1 mole MnO4- [Fe2+] = 0.0250 L = 0.135 M

Inert electrodes- look at the solution for the reactions 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- → Mn2+ + 4H2O Anode: H2O2 → O2 + 2H+ + 2e- What happens to the mass of the cathode? Constant What happens to the mass of the anode? What happens to the pH of the cathode? Increases What happens to the pH of the anode? Decreases

The Cathode will stay inert A non-inert Anode might oxidize Non-Inert Electrodes The Cathode will stay inert A non-inert Anode might oxidize DC Power - + Cu might oxidize - Cathode Reduction 2H2O + 2e-→H2 +2OH- -0.41 v Cu Cu K+ SO42- H2O K2SO4(aq)

You must look at the possible oxidation of: SO42- H2O Cu Strongest Reducing Agent

The Cathode will stay inert A non-inert Anode might oxidize Non-Inert Electrodes The Cathode will stay inert A non-inert Anode might oxidize DC Power - + Cu might oxidize Cu Cu K+ SO42- H2O - Cathode Reduction 2H2O + 2e-→H2 +2OH- -0.41 v + Anode Oxidation Cu(s) → Cu2+ + 2e- -0.34 v K2SO4(aq)

Review of Cells Electrochemical Electrolytic   Is a power supply Requires power supply Spontaneous (+) Nonspontaneous (-) Makes electricity 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.

Electrochemical Cell: Zn, Zn(NO3)2 II Cu, CuSO4 Complete the Chart   Electrochemical Cell: Zn, Zn(NO3)2 II Cu, CuSO4 Anode: Reaction: Cathode: Reaction: E0 =   Zn Zn(s) → Zn2+ + 2e- 0.76 v Cu Cu2+ + 2e- → Cu(s) 0.34 v 1.10 v Higher on reduction Chart

Electrolytic Cell: Molten AlCl3 Anode: Reaction: Cathode: Reaction:   Anode: Reaction: Cathode: Reaction: Al3+ Cl- C 2Cl- → Cl2(g) + 2e- -1.36 v   Al3+ + 3e- → Al(s) -1.66 v C E0 = -3.02 v MTV = +3.02 v The anode and cathode are inert C or Pt Vowels: Anode Anion Oxidation Consonants: Cathode Cation Reduction

Anode: Cathode: C C Anode Oxidation Anion or Water  Electrolytic Cell: KBr(aq) K+ Br- H2O   Anode: Cathode:    C C Anode Oxidation Anion or Water

Oxidation of water

Anode: 2Br- → Br2(g) + 2e- -1.09 v Cathode: C C  Electrolytic Cell: KBr(aq) K+ Br- H2O   Anode: 2Br- → Br2(g) + 2e- -1.09 v Cathode:    C C Anode Oxidation Anion or Water Cathode Reduction Cation or water

Anode: 2Br- → Br2(g) + 2e- -1.09 v  Electrolytic Cell: KBr(aq) K+ Br- H2O   Anode: 2Br- → Br2(g) + 2e- -1.09 v Cathode: 2H2O + 2e- → H2(g) + 2OH- -0.41 v    C C 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 Drunks Jeff Dunham