Chemical substances are categorized as acids or bases, each with distinct properties. This article will explore the nature of chemical bases and specifically investigate if calcium hydroxide (Ca(OH)2) qualifies as an Arrhenius base.
Defining Arrhenius Bases
The Arrhenius theory, proposed by Swedish chemist Svante Arrhenius in 1884, defines acids and bases by their behavior in aqueous solutions. An Arrhenius base is any substance that increases the concentration of hydroxide ions (OH⁻) when dissolved in water. This occurs as the substance dissociates into its constituent ions.
Sodium hydroxide (NaOH) is a common example of an Arrhenius base. When added to water, it fully dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). The chemical equation for this dissociation is NaOH(aq) → Na⁺(aq) + OH⁻(aq). This process directly contributes to a higher concentration of hydroxide ions in the solution.
Other Arrhenius bases include lithium hydroxide (LiOH) and potassium hydroxide (KOH), both Group 1 metal hydroxides. These compounds release hydroxide ions into the solution upon dissociation. The presence of these hydroxide ions is the defining characteristic of an Arrhenius base, enabling the solution to exhibit basic properties.
Calcium Hydroxide Meets the Definition
Calcium hydroxide (Ca(OH)₂) meets the Arrhenius definition of a base. When it dissolves in water, it dissociates to produce calcium ions (Ca²⁺) and hydroxide ions (OH⁻). The dissociation equation is: Ca(OH)₂(aq) → Ca²⁺(aq) + 2OH⁻(aq). This shows that for every unit of Ca(OH)₂ that dissolves, two hydroxide ions are released.
Although calcium hydroxide is sparingly soluble in water, the portion that does dissolve completely dissociates. For instance, its solubility at 20°C is approximately 1.73 grams per liter. This dissolution, even if limited, is sufficient to increase the concentration of hydroxide ions in the aqueous solution, fulfilling the criteria for an Arrhenius base.
The production of hydroxide ions as the only negative ions further confirms its classification as an Arrhenius base. The increased hydroxide ion concentration leads to a rise in the solution’s pH, indicating its basic nature. Thus, despite its moderate solubility, calcium hydroxide effectively acts as an Arrhenius base due to its ability to release hydroxide ions into water.
Practical Uses of Calcium Hydroxide
Calcium hydroxide, known as slaked lime or hydrated lime, finds widespread application across various industries due to its basic properties. In agriculture, it is used as a liming agent to neutralize acidic soils, improving nutrient availability for crops and promoting healthier plant growth.
In water treatment, calcium hydroxide serves multiple functions. It adjusts the pH of acidic water, preventing pipe corrosion. It also acts as a flocculant, clumping suspended particles in water, which then settle out, leading to clearer water. It aids in removing heavy metals and phosphates from wastewater through precipitation.
The construction industry utilizes calcium hydroxide extensively in mortar, plaster, and cement production. When mixed with sand and water, it forms a paste that hardens by reacting with atmospheric carbon dioxide, contributing to the strength and durability of building materials. Its ability to improve workability and strength makes it a valuable component.
Calcium hydroxide, identified as food additive E526, also plays a role in the food industry. It is used to clarify sugar cane and sugar beet juices during refining. It also enhances crispness in pickling vegetables and aids in maize preparation to remove kernels’ hulls.