UCSD Chemistry & Biochemistry - Lecture Demonstrations

DEMONSTRATIONS

Lecture Room Volt Meter

Procedure

Cut wedges out of a piece of 9cm filter paper so that three equal spokes ~1cm wide are left (should look like a 'Y'). Cut the tips off so the 'Y' fits into the dispo petri dish. .
Place 2-3 drops 1M CuSO₄ at one end of the 'Y', repeat with 1M ZnSO₄, and 1M Pb(NO₃)₂. The solutions will start to wick along the paper. Before they merge add 1-2 drops 1M Na₂SO₄ (salt bridge) to the center of the 'Y' to stop the wicking. .
Position 1cm² pieces of Zn, Cu, and Pb over their salts at the tips of the 'Y'. .
With the meter set on center zero, measure the voltage. Switching leads shows direction of electron flow. Be sure the 3V module is in place.
Reactions E (volts)

Cu²⁺ + 2e- --> Cu (s) 0.337
Pb²⁺ + 2e- --> Pb (s) -0.126
Zn²⁺ + 2e- --> Zn (s) -0.7628
  
Lead
        
Voltage Observed
(-) (+) Lecture Meter Fluka Meter Literature*
Zn Cu 1.1 1.091 1.0998
PB 0.6 0.599 0.6368
   
Pb Zn 0.6 0.599 0.6368
Cu -0.5 -0.488 -0.463
   
Cu Zn -1.1 -1.091 -1.0998
Pb -0.5 -0.488 -0.463
*Quantitative Chemistry, Jurg Waser

Reactions	E (volts)
Cu²⁺ + 2e- --> Cu (s)	0.337
Pb²⁺ + 2e- --> Pb (s)	-0.126
Zn²⁺ + 2e- --> Zn (s)	-0.7628

Lead			Voltage Observed
(-)	(+)	Lecture Meter	Fluka Meter	Literature*
Zn	Cu	1.1	1.091	1.0998
	PB	0.6	0.599	0.6368

Pb	Zn	0.6	0.599	0.6368
	Cu	-0.5	-0.488	-0.463

Cu	Zn	-1.1	-1.091	-1.0998
	Pb	-0.5	-0.488	-0.463

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Last Updated: 5/23/02