Question

What is the shorthand notation for a galvanic cell that uses the reaction shown below?

1) 3Zn(s)+Cr2O72−(aq)+14H+(aq)→3Zn2+(aq)+2Cr3+(aq)+7H2O(l)

2) 2Al(s)+3Fe2+(aq)→2Al3+(aq)+3Fe(s)

Answer 1

Okr, first some rules:

1. The anode (electrons at products) half-cell is described first; the cathode (electrons al reactants) half-cell follows. Within a given half-cell, the reactants are specified first and the products last. The description of the oxidation reaction is first, and the reduction reaction is last; when you read it, your eyes move in the direction of electron flow. Spectator ions are not included.

2. A single vertical line ( | ) is drawn between two chemical species that are in different phases but in physical contact with each other (e.g., solid electrode | liquid with electrolyte). A double vertical line ( || ) represents a salt bridge or porous membrane separating the individual half-cells.

3. The phase of each chemical (s, l, g, aq) is shown in parentheses. If the electrolytes in the cells are not at standard conditions, concentrations and/or pressure, they are included in parentheses with the phase notation. If no concentration or pressure is noted, the electrolytes in the cells are assumed to be at standard conditions (1.00 M or 1.00 atm and 298 K).

1) 3Zn_(s)+Cr₂O₇²⁻_(aq)+14H⁺_(aq)→3Zn²⁺_(aq)+2Cr³⁺_(aq)+7H₂O_(l)

Anode: 3Zn_(s)→3Zn²⁺_(aq) + 6 e^-

Cathode: Cr₂O₇²⁻_(aq)+14H⁺_(aq) + 6e^-→2Cr³⁺_(aq)+7H₂O_(l)

Shorthand notation: Zn_(s)|Zn²⁺_(aq) || Cr₂O₇²⁻_(aq)|Cr³⁺_(aq)|H₂O_(l)|H⁺_(aq)

2) 2Al_(s)+3Fe²⁺_(aq)→2Al³⁺_(aq)+3Fe_(s)

Anode:2Al_(s)→2Al³⁺_(aq) + 6e^-

Cathode:3Fe²⁺_(aq)+6e^-→3Fe_(s)

Shorthand Notation: Al_(s)|Al³⁺_(aq)||Fe²⁺_(aq)|Fe_(s)