Electrochemical Cells Using Sodium Silicate

20.5 Electrochemical Cells Using Sodium Silicate

Chemical Concepts Demonstrated: Galvanic and voltaic cells

Demonstration:

The silicate gel is made up of sodium silicate dissolved in water and a Cu²⁺solution made of Cu(NO₃)₂ * H₂O dissolved in water with acetic acid.

A copper metal electrode is inside the gel.
A metal ion solution (Ag⁺, Zn²⁺, or Pb²⁺) is poured over the gel.
A corresponding metal electrode is placed in the solution.

Observations:

The gel allows the copper metal to act as a voltaic cell with the metal ion solution.

Explanation (including chemical equations):

The Ag⁺/Ag half-cell coupled with the Cu²⁺/Cu half-cell yields a standard-state cell potential of 0.46 V.

anode:	Cu (s) ---> Cu²⁺ (aq) + 2 e^-	E^o= - 0.34 V
cathode:	Ag⁺ (aq) + e^----> Ag(s)	E^o= 0.80 V
	Cu (s) + 2 Ag⁺ (aq) ---> Cu²⁺ (aq) + 2 Ag(s)	E^o_cell = 0.46 V

If the Ag⁺/Ag half-cell is replaced using the Pb²⁺/Pb or the Zn²⁺/ Zn half reactions, the leads to the voltmeter would need to be reversed in order to set up a volaic cell:

anode:	Cu (s) ---> Cu²⁺ (aq) + 2 e^-	E^o= - 0.34 V
cathode:	Pb²⁺ (aq) + 2 e^----> Pb (s)	E^o= - 0.13 V
	Cu (s) + Pb²⁺ (aq) ---> Cu²⁺ (aq) + Pb (s)	E^o_cell = -0.47 V

or:

anode:	Cu (s) ---> Cu²⁺ (aq) + 2 e^-	E^o= - 0.34 V
cathode:	Zn²⁺ (aq) + 2 e^----> Zn (s)	E^o= - 0.76 V
	Cu (s) + Zn²⁺ (aq) ---> Cu²⁺ (aq) + Zn (s)	E^o_cell = -1.10 V