Yes, OH$^{-}$ (hydroxide ion) is indeed considered a strong base. This means that when hydroxide compounds dissolve in water, they completely dissociate, releasing all their hydroxide ions into the solution.
What Makes a Base Strong?
A strong base is fundamentally characterized by its ability to completely ionize or dissociate in an aqueous solution. This process releases hydroxide ions (OH$^{-}$), which are powerful proton acceptors. The greater the concentration of free OH$^{-}$ ions in a solution, the higher its alkalinity and pH value.
Key characteristics of strong bases include:
- Complete Dissociation: When a strong base dissolves in water, every molecule breaks apart into its constituent ions. For hydroxides, this means 100% of the base forms metal cations and hydroxide anions.
- High pH Value: Solutions of strong bases typically have a pH of 13 or 14 (at standard concentrations), indicating a very high concentration of hydroxide ions.
- Strong Electrolytes: Due to their complete dissociation into ions, strong bases are excellent conductors of electricity in solution.
- Corrosive Nature: Strong bases are highly corrosive and can cause severe chemical burns to skin and damage to many materials.
The Role of Hydroxide Ions (OH⁻)
The hydroxide ion (OH⁻) itself is the active component responsible for the basic properties. When a compound like sodium hydroxide (NaOH) dissolves in water, it breaks down into Na⁺ and OH⁻ ions. It is the presence of these freely available OH⁻ ions that makes the solution basic. The higher the concentration of these ions, the stronger the base.
Common Strong Bases
Most strong bases are hydroxides of Group 1 and Group 2 metals from the periodic table. Here are some prominent examples:
- Group 1 Hydroxides (Alkali Metal Hydroxides):
- Sodium Hydroxide (NaOH): Commonly known as lye or caustic soda.
- Potassium Hydroxide (KOH): Also known as caustic potash.
- Lithium Hydroxide (LiOH):
- Rubidium Hydroxide (RbOH):
- Cesium Hydroxide (CsOH):
- Group 2 Hydroxides (Alkaline Earth Metal Hydroxides): These are generally less soluble than Group 1 hydroxides but are still considered strong bases because the portion that does dissolve dissociates completely.
- Calcium Hydroxide (Ca(OH)₂): Known as slaked lime.
- Strontium Hydroxide (Sr(OH)₂):
- Barium Hydroxide (Ba(OH)₂):
| Feature | Strong Base | Weak Base |
|---|---|---|
| Dissociation | Complete (100%) in water | Partial (less than 100%) in water |
| OH⁻ Release | High concentration of free OH⁻ | Low concentration of free OH⁻ |
| pH Range | Typically 13-14 | Typically 8-11 |
| Conductivity | Strong electrolyte (high conductivity) | Weak electrolyte (low conductivity) |
| Examples | NaOH, KOH, Ca(OH)₂ | NH₃ (Ammonia), C₅H₅N (Pyridine) |
Properties and Applications of Strong Bases
Strong bases like those containing the hydroxide ion are crucial in various industrial, laboratory, and household applications due to their reactive nature and ability to neutralize acids.
- Neutralization Reactions: They are used to neutralize acidic solutions, producing salt and water.
- Industrial Manufacturing: Employed in the production of soaps, detergents, paper, textiles, and various chemicals. For example, NaOH is vital in the saponification process.
- Drain Cleaners: The corrosive nature of strong bases (like NaOH in drain cleaners) helps dissolve grease and organic matter in clogged pipes.
- Water Treatment: Used to adjust the pH of water and precipitate heavy metals.
- Laboratory Reagents: Essential reagents in many chemical experiments and titrations to determine acid concentrations.
Safety Precautions
Given their highly corrosive nature, strong bases containing the hydroxide ion require careful handling.
- Always wear appropriate personal protective equipment (PPE) such as safety goggles, gloves, and lab coats.
- Avoid direct skin or eye contact. In case of contact, rinse immediately with plenty of water and seek medical attention.
- When diluting, always add the base slowly to water, never the other way around, to control the exothermic reaction.
- Store in appropriate, labeled containers away from acids and incompatible materials.
Chemistry
