Alkali Metal Hydroxides

Definition

Alkali metal hydroxides are a class of strong ionic compounds formed by the combination of an alkali metal (such as lithium, sodium, potassium, rubidium, or cesium) and a hydroxide ion (OH-). These highly basic compounds are characterized by their ability to dissociate in water, producing a high concentration of hydroxide ions and resulting in a pH greater than 7.

5 Must Know Facts For Your Next Test

1. Alkali metal hydroxides are highly soluble in water, producing solutions with a high pH due to the abundance of hydroxide ions.
2. These compounds are strong bases, capable of neutralizing acids and undergoing acid-base reactions.
3. Alkali metal hydroxides are commonly used in various industrial and commercial applications, such as in the production of soaps, detergents, and cleaning agents.
4. The strength of the basicity of alkali metal hydroxides increases from lithium hydroxide to cesium hydroxide, with sodium hydroxide and potassium hydroxide being the most commonly used.
5. Alkali metal hydroxides can react with alkynes to form acetylide anions, which are important intermediates in organic synthesis.

Review Questions

• Explain the formation of acetylide anions from the reaction of alkynes with alkali metal hydroxides.
  • Alkynes, which are organic compounds containing a carbon-carbon triple bond, can undergo a reaction with alkali metal hydroxides to form acetylide anions. In this process, the highly basic hydroxide ion (OH-) from the alkali metal hydroxide deprotonates the terminal hydrogen of the alkyne, resulting in the formation of a negatively charged acetylide anion. This acetylide anion can then participate in further organic reactions, making it an important intermediate in organic synthesis.
• Describe the relationship between the strength of alkali metal hydroxides and their ability to form acetylide anions.
  • The strength of the basicity of alkali metal hydroxides is directly related to their ability to form acetylide anions from alkynes. As the alkali metal hydroxides become more basic, moving down the periodic table from lithium to cesium, their ability to deprotonate the terminal hydrogen of alkynes and generate the acetylide anion intermediates increases. This is because the more basic the hydroxide ion, the more readily it can accept a proton from the alkyne, facilitating the formation of the desired acetylide anion.
• Analyze the role of alkali metal hydroxides in the context of 9.7 Alkyne Acidity: Formation of Acetylide Anions, and explain how their properties contribute to this process.
  • In the context of 9.7 Alkyne Acidity: Formation of Acetylide Anions, alkali metal hydroxides play a crucial role. The high basicity of these compounds, stemming from their ability to dissociate in water and produce a high concentration of hydroxide ions, allows them to effectively deprotonate the terminal hydrogen of alkynes. This deprotonation step leads to the formation of acetylide anions, which are important intermediates in organic synthesis. The strength of the basicity of the alkali metal hydroxides, increasing from lithium to cesium, directly influences their capacity to facilitate this key step in the formation of acetylide anions, making them essential reagents in this context.

Related terms

Alkali Metals: The alkali metals are a group of highly reactive elements in the periodic table, including lithium, sodium, potassium, rubidium, and cesium. They are known for their low ionization energies and tendency to form positive ions.

Hydroxide Ion:

The hydroxide ion (OH-) is a negatively charged species consisting of an oxygen atom bonded to a hydrogen atom. It is a strong base that can accept protons, leading to the formation of water.

pH:

pH is a measure of the acidity or basicity of a solution, with a range from 0 to 14. Solutions with a pH greater than 7 are considered basic, and those with a pH less than 7 are considered acidic.