Electrochemistry, Corrosion, and Acid-Base Chemistry

Galvanic Reaction in the Mouth

Biting on aluminum foil can be painful and is usually noticed if you have metal in your mouth from dental work (e.g., fillings, crowns). Basically, when you bite on foil, you set up a battery in your mouth, and the electrical current stimulates nerve endings in your tooth. Here is what happens:

• Pressure from biting brings two dissimilar metals (aluminum foil, mercury in fillings, or gold in crowns) in contact in a moist, salty environment (saliva).
• The two metals have an **electrochemical potential difference** or voltage across them.
• Electrons flow from the foil into the tooth (i.e., **electrical current**).
• The current gets conducted into the tooth's root, usually by the filling or crown.
• The current sets off a nerve impulse in the root's nerve.
• The nerve impulse is sent to the brain.
• The brain interprets the impulse as pain.

Climate Effects on Oxidation

**Wet climates** obviously have **more** water **than** drier **climates**. Metals, when subject to water, have the tendency to oxidize (**rust**). Therefore, if water is barely present in a **climate**, then oxidation is also least likely to occur.

Primary and Secondary Cells Explained

A **primary cell** cannot be recharged, whereas a **secondary cell** can be recharged. In a **primary cell**, the chemical reaction is irreversible, whereas in a **secondary cell**, the chemical reaction is reversible. Examples include a remote control battery (**primary**) and a phone battery (**secondary**).

Methods to Prevent Corrosion

• **Metal Type**: Choosing corrosion-resistant metals.
• **Protective Coating**: Applying barriers like paint or plating.

Understanding Acid Concentration

The **concentration** tells you about how much of the original **acid** is dissolved in the solution. It is perfectly **possible to have a concentrated** solution of a **weak acid**, or a dilute solution of a strong **acid**.

Ammonia: A Bronsted-Lowry Base

Since ammonia does NOT contain hydroxide ions (OH^–), i.e., its chemical formula is **NH₃**, it does not fall under the Arrhenius' umbrella. We classify ammonia as a **Bronsted-Lowry base**, and its **conjugate acid** is the ammonium ion, **NH₄⁺**.

Arrhenius Acid and Base Definitions

An **Arrhenius acid** increases the concentration of hydrogen (H⁺) ions **in an** aqueous solution, while an **Arrhenius base** increases the concentration of hydroxide (OH^–) ions **in an** aqueous solution.

Conjugate Acid-Base Pairs

The term **conjugate** refers to an acid and base that differ from each other by a proton. When an acid and base react, the acid forms its **conjugate base**, while the base forms its **conjugate acid**.