Identifying Bases Which Of The Following Is A Base AgO $Ca ( OH )_2$ HF NaCl

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Determining which of the following is a base is a fundamental concept in chemistry. In this comprehensive guide, we will delve into the definition of bases, explore the properties that characterize them, and then analyze the given options—AgO, $Ca(OH)_2$, HF, and NaCl—to identify the correct base. Understanding bases is crucial for grasping acid-base chemistry, which plays a vital role in numerous chemical reactions and biological processes. This article aims to provide a clear and thorough explanation, ensuring that you can confidently identify bases in various chemical contexts.

Defining Bases in Chemistry

In chemistry, a base is a substance that can accept hydrogen ions ($H^+$) or donate hydroxide ions ($OH^-$) in aqueous solutions. This definition, while seemingly simple, encompasses a wide range of chemical compounds with diverse properties. Bases are essential components of acid-base reactions, which are ubiquitous in both natural and synthetic chemical systems. To fully understand what constitutes a base, it is important to explore different definitions and theories that describe their behavior.

Arrhenius Definition of Bases

The Arrhenius definition was one of the earliest attempts to classify acids and bases. According to Svante Arrhenius, a Swedish scientist, an Arrhenius base is a substance that, when dissolved in water, increases the concentration of hydroxide ions ($OH^-$). Common examples of Arrhenius bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH). These compounds dissociate in water to release hydroxide ions, thereby increasing the basicity of the solution. The Arrhenius definition, while useful, is limited because it only applies to aqueous solutions and does not account for bases that do not contain hydroxide ions.

Brønsted-Lowry Definition of Bases

The Brønsted-Lowry definition offers a broader perspective on acids and bases. Proposed independently by Johannes Brønsted and Thomas Lowry, this definition states that a Brønsted-Lowry base is any substance that can accept a proton ($H^+$). This definition expands the scope of what can be considered a base, as it includes substances that do not necessarily produce hydroxide ions in solution. For example, ammonia ($NH_3$) is a Brønsted-Lowry base because it can accept a proton to form ammonium ion ($NH_4^+$). This definition is particularly useful in non-aqueous solutions and in understanding reactions where proton transfer occurs.

Lewis Definition of Bases

The Lewis definition provides the most comprehensive view of acids and bases. According to Gilbert N. Lewis, a Lewis base is any substance that can donate a pair of electrons to form a chemical bond. This definition encompasses all Brønsted-Lowry bases and extends to substances that do not even contain hydrogen. For example, the hydroxide ion ($OH^-$), ammonia ($NH_3$), and water ($H_2O$) are all Lewis bases because they have lone pairs of electrons that can be donated. This definition is crucial in understanding reactions involving coordination complexes and other chemical interactions where electron donation is central.

Properties of Bases

Understanding the properties of bases is essential for identifying them. Bases exhibit several characteristic traits that distinguish them from acids and other chemical compounds. These properties include:

  1. Taste: Bases typically have a bitter taste. However, tasting chemicals in a lab setting is dangerous and should never be done.
  2. Feel: Bases often feel slippery or soapy to the touch. This is due to their reaction with the oils on the skin.
  3. Reaction with Acids: Bases neutralize acids, forming a salt and water. This is the fundamental principle behind acid-base titrations.
  4. pH: Bases have a pH greater than 7. A pH of 7 is neutral, values below 7 indicate acidity, and values above 7 indicate basicity.
  5. Litmus Paper Test: Bases turn red litmus paper blue.
  6. Phenolphthalein Indicator: Bases turn phenolphthalein indicator pink.

Analyzing the Given Options

Now, let's apply our understanding of bases to the given options: AgO, $Ca(OH)_2$, HF, and NaCl. We will analyze each option based on the definitions and properties discussed to determine which one is a base.

A. AgO (Silver Oxide)

AgO, or silver oxide, is a compound of silver and oxygen. While it might seem like a metallic oxide could exhibit basic properties, AgO is amphoteric, meaning it can act as both an acid and a base under different conditions. However, it does not readily dissociate to produce hydroxide ions in water, nor does it strongly accept protons. Therefore, AgO is not typically considered a strong base. Its amphoteric nature is more complex, and its behavior depends on the specific reaction conditions. In most common scenarios, it does not behave as a typical base like hydroxides of alkali or alkaline earth metals.

B. $Ca(OH)_2$ (Calcium Hydroxide)

Ca(OH)_2$, or **calcium hydroxide**, is a classic example of a base. According to the Arrhenius definition, it is a base because it dissociates in water to produce hydroxide ions ($OH^-$): $Ca(OH)_2 (s) ightleftharpoons Ca^{2+}(aq) + 2OH^-(aq)

Calcium hydroxide is also a Brønsted-Lowry base because the hydroxide ions can accept protons. Furthermore, it exhibits the characteristic properties of bases, such as a bitter taste (though tasting it is not recommended), a slippery feel in solution, and the ability to turn red litmus paper blue. It is commonly used in various applications, including the production of cement and in agriculture to neutralize acidic soils. The presence of hydroxide ions directly classifies it as a base, making it a clear-cut example.

C. HF (Hydrofluoric Acid)

HF, or hydrofluoric acid, is an acid, not a base. It is a weak acid, meaning it does not completely dissociate in water, but it still donates protons ($H^+$) rather than accepting them. The dissociation of HF in water can be represented as:

HF(aq)+H2O(l)ightleftharpoonsH3O+(aq)+F−(aq)HF(aq) + H_2O(l) ightleftharpoons H_3O^+(aq) + F^-(aq)

Hydrofluoric acid is known for its corrosive properties and its ability to dissolve glass. It is used in various industrial applications, including etching glass and cleaning metal. Due to its acidic nature, HF is not a base and is, in fact, the opposite; it is a proton donor rather than a proton acceptor.

D. NaCl (Sodium Chloride)

NaCl, or sodium chloride, is common table salt. It is a neutral salt formed from the reaction of a strong acid (HCl) and a strong base (NaOH). When dissolved in water, it dissociates into sodium ions ($Na^+$) and chloride ions ($Cl^-$):

NaCl(s)ightarrowNa+(aq)+Cl−(aq)NaCl(s) ightarrow Na^+(aq) + Cl^-(aq)

Neither of these ions significantly affects the pH of the solution, so NaCl is considered neutral. It does not produce hydroxide ions nor does it accept protons, thus it is neither an acid nor a base. Sodium chloride is essential for various biological and industrial processes, but it does not exhibit basic properties.

Conclusion

In summary, when evaluating which of the options is a base, the correct answer is $Ca(OH)_2$ (calcium hydroxide). Calcium hydroxide fits the definitions of a base by Arrhenius, Brønsted-Lowry, and Lewis, as it dissociates to produce hydroxide ions in water and can accept protons. The other options, AgO, HF, and NaCl, do not exhibit the characteristics of bases. AgO is amphoteric but not a strong base, HF is an acid, and NaCl is a neutral salt. Understanding the definitions and properties of bases is crucial for identifying them accurately in various chemical contexts.

This discussion should provide a comprehensive understanding of bases and help in identifying them in chemical problems. By reviewing the definitions of Arrhenius, Brønsted-Lowry, and Lewis bases, along with the characteristic properties of bases, you can confidently determine whether a given substance is a base or not.