Chapter 21: Electrochemistry Table of Contents Chapter 21: Electrochemistry 21.1 – Voltaic Cells

Review Zn + NiSO4 → Ni + ZnSO4 Basic Assessment Questions Review Identify what is oxidized and what is reduced. Zn + NiSO4 → Ni + ZnSO4 Ox: Zn Red: Ni2+ Define Redox reactions Oxidation Reduction Half-reactions

Electrochemistry is using chemistry to create electricity Electrochemistry: Basic Concepts Electrochemistry is using chemistry to create electricity Electrical current: The flow of electrons in a certain direction Redox reactions can produce an electrical current. This is what occurs in a battery—one form of an electrochemical cell

Electrochemical cell: a device that uses Electrochemistry: Basic Concepts Definitions Electrochemical cell: a device that uses redox reactions to create electricity OR electric energy to cause chemical reactions Voltaic or galvanic cell: creates electricity by a spontaneous redox reaction. a type of electrochemical cell.

Balanced: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) Total ionic: Zn(s) + Cu2+(aq) + SO42-(aq) → Zn2+(aq) + SO42-(aq) + Cu(s) Net ionic: Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) ox red Half Reactions: Zn(s) → Zn2+(aq) + 2e- Half Reactions: Zn(s) → Zn2+(aq) + 2e- Cu2+(aq) + 2e-→ Cu(s)

Electrochemical Cell Zinc strip Copper strip Cannot transfer e- SO42- SO42- CuSO4(aq) ZnSO4(aq) Zn2+ Cu2+ Zn(s) → Zn2+(aq) + 2e- Cu2+(aq) + 2e-→ Cu(s)

Electrochemical Cell Allows e- transfer Copper wire (+) charge builds up in one solution, (-) charge builds up in the other

Allows ions to pass from one side to the other Electrochemical Cell Allows ions to pass from one side to the other Ions pass through plugs in the bridge, but solutions do not mix Salt bridge KCl Circles = plug, algae gel

Electrochemical Cell Zn → Zn2+ + 2e- Cu2+ + 2e- → Cu e- flow K+ Cl- e- e- Cl- K+ e- e- Zn Cl- K+ Cu Circles = plug, algae gel Zn2+ Cu2+ Zn → Zn2+ + 2e- Cu2+ + 2e- → Cu

What is this called? What does it do? Why can redox reactions create electricity? e- flow KCl Zn Cu Circles = plug, algae gel 1M Zn2+ 1M Cu2+ Zn → Zn2+ + 2e- Cu2+ + 2e- → Cu

Voltaic/Galvanic Cell e- flow KCl electrodes electrodes half-cells Zn Cu Circles = plug, algae gel Zn2+ Cu2+ electrolytes

Electrolytes: a solution of ions Electrochemistry: Basic Concepts Definitions Half-cells: Where oxidation and reduction reactions separately take place (2 parts) Electrode: an object in the half-cell that conducts electrons to or from another substance – immersed in electrolytes Electrolytes: a solution of ions

Voltaic/Galvanic Cell Voltaic Cell e- flow KCl Zn Cu oxidation ANODE Circles = plug, algae gel reduction CATHODE 1M Zn2+ 1M Cu2+ Zn → Zn2+ + 2e- Cu2+ + 2e- → Cu

Anode: The electrode where oxidation takes place Electrochemistry: Basic Concepts Definitions Anode: The electrode where oxidation takes place Cathode: The electrode where reduction takes place Electrons always flow from the anode to the cathode

Let’s see it

On the following slides, identify… Salt bridge What is oxidized Electrochemistry: Basic Concepts Practice On the following slides, identify… Salt bridge What is oxidized What is reduced Cathode Anode Direction of e- flow through wire

Voltaic/Galvanic Cell oxidized reduced

Voltaic/Galvanic Cell e- flow

Voltaic/Galvanic Cell Salt bridge