Question

An electrochemical cell that produces a current from an oxidation-reduction reaction is often called a(n) ________ cell.

Short answer

A(n) \(\underline{\text{galvanic (voltaic)}}\) cell.

Step-by-step solution

Recall the types of electrochemical cells

There are two main types of electrochemical cells: galvanic (voltaic) cells and electrolytic cells. Galvanic cells produce a spontaneous redox reaction to generate an electrical current, while electrolytic cells use an external electrical current to drive a non-spontaneous redox reaction.

Identify the correct type

The exercise mentions that the electrochemical cell produces a current from an oxidation-reduction reaction. From the types of cells discussed above, it's clear that the required electrochemical cell is a galvanic (voltaic) cell, as it generates an electrical current through a spontaneous redox reaction. Therefore, the answer is: A(n) \(\underline{\text{galvanic (voltaic)}}\) cell.

Key concepts

Galvanic Cell

A galvanic cell, also known as a voltaic cell, is a type of electrochemical power source that generates electricity through spontaneous redox reactions. It's fascinating to know that this process is the chemical foundation of battery technology. Inside a galvanic cell, two different metals, called electrodes, are immersed in electrolyte solutions and are connected externally by a conductive wire and internally by a salt bridge.

The beauty of galvanic cells lies in their ability to convert chemical energy directly into electrical energy. The two electrodes each experience different half-reactions: one metal undergoes oxidation (losing electrons) and the other undergoes reduction (gaining electrons). The flow of electrons from the oxidizing to the reducing agent through the wire is what generates the current.

To further explain, consider the classic example of a zinc-copper galvanic cell, where zinc is the anode and copper is the cathode:

• Zinc electrode (anode): Zn → Zn²⁺ + 2e⁻ (oxidation)
• Copper electrode (cathode): Cu²⁺ + 2e⁻ → Cu (reduction)

By connecting devices to this flow, we can harness this electric current for practical use.

Redox Reaction

Redox reactions, short for reduction-oxidation reactions, are processes where electrons are transferred between substances. They are the heart of understanding how electrochemical cells work. In any redox reaction, two processes occur simultaneously: oxidation, where a substance loses electrons, and reduction, where another substance gains those electrons. The substance that gives away electrons is called the reducing agent, while the receiver is termed the oxidizing agent.

An easy way to remember this is with the mnemonic 'OIL RIG' – Oxidation Is Loss, Reduction Is Gain. When writing redox reactions, we depict the movement of electrons and show how the charge on atoms or molecules changes. A nice example is the reaction between hydrogen and oxygen to form water:

• Oxidation: 2H₂ → 4H⁺ + 4e⁻
• Reduction: O₂ + 4e⁻ → 2O²⁻

From a student's perspective, balancing redox reactions involves ensuring that the same number of electrons are lost and gained, thus maintaining charge neutrality. Complex as it may seem, mastering redox reactions is essential for solving many chemistry problems and understanding electron transfer in biology, geology, and environmental science.

Electrolytic Cell

An electrolytic cell is the reverse cousin of the galvanic cell. In this setup, electrical energy is consumed to drive a non-spontaneous chemical reaction. Imagine having to push a ball uphill instead of watching it roll down by gravity – that's what external energy does in an electrolytic cell. This process is widely used in industry for things like electroplating, refining metals, and even producing elements like chlorine and sodium through the electrolysis of saltwater.

Here's how an electrolytic cell works: when external voltage is applied across the electrodes, positively charged ions (cations) move to the cathode to gain electrons (reduce), and negatively charged ions (anions) move to the anode to lose electrons (oxidize). Unlike galvanic cells, the anode in an electrolytic cell is positive because it is attached to the positive terminal of the power source, and the cathode is negative.

For example, during the electrolysis of molten sodium chloride (NaCl), we see:

• Cathode (reduction): Na⁺ + e⁻ → Na
• Anode (oxidation): 2Cl⁻ → Cl₂(g) + 2e⁻

Through understanding electrolytic cells, students gain insight into the practical applications of chemistry in technology and manufacturing. Being able to predict the outcome of electrolysis by knowing the reactants and the type of cell gives a significant edge in chemical sciences.