Question

State as to why (a) a solution of \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) is alkaline? (b) alkali metals are prepared by electrolysis of their fused chlorides? (c) sodium is found to be more useful than potassium?

Short answer

(a) Formation of \\(\mathrm{OH^-}\\) ions makes \\(\mathrm{Na_2CO_3}\\) alkaline. (b) Electrolysis avoids oxidation of alkali metals. (c) Sodium is safer and more abundant than potassium.

Step-by-step solution

- Understanding \\(\mathrm{Na_2CO_3}\\) and its Alkalinity

A solution of \(\mathrm{Na_2CO_3}\) is alkaline because it dissociates in water to form \(\mathrm{Na^+}\) ions and \(\mathrm{CO_3^{2-}}\) ions. The carbonate ion (\(\mathrm{CO_3^{2-}}\)) readily reacts with water (which is neutral) to form bicarbonate (\(\mathrm{HCO_3^-}\)) and hydroxide ions (\(\mathrm{OH^-}\)), increasing the hydroxide ion concentration in the solution and making it alkaline.

- Electrolysis for Alkali Metal Preparation

Alkali metals are prepared by electrolysis of their fused chlorides because these metals are highly reactive and cannot be produced by chemical reduction of their oxides with carbon. The electrolysis of fused chlorides helps in obtaining these metals in their pure form due to the high melting points that prevent their oxidation at elevated temperatures and allow efficient separation of the metal from the chloride ions.

- Comparing the Usefulness of Sodium and Potassium

Sodium is found to be more useful than potassium because it is more abundant, less reactive with water, and thus safer to handle. Sodium is widely used in various industries, including in the synthesis of organic compounds, as a heat exchanger fluid, and in sodium vapor lamps, while potassium's higher reactivity limits its practical applications outside of specific contexts such as fertilizers.

Key concepts

Alkalinity of Sodium Carbonate

Sodium carbonate, often known as washing soda, exemplifies alkalinity owing to its interaction with water. When dissolved, it separates into sodium ions \((\mathrm{Na^+})\) and carbonate ions \((\mathrm{CO_3^{2-}})\). The pivotal role is played by the carbonate ion. It reacts with water molecules in the solution to form bicarbonate ions \((\mathrm{HCO_3^-})\) and hydroxide ions \((\mathrm{OH^-})\). The production of hydroxide ions is crucial here since it characterizes the solution as alkaline. This is because hydroxide ions increase the basicity and raise the pH above the neutral point of 7.
Understanding this reaction is vital for recognizing why sodium carbonate is often used in processes like water softening and pH regulation.

• The presence of more hydroxide ions contributes to the solution being more basic.
• Sodium carbonate's alkaline nature makes it effective in neutralizing acidic substances.

Electrolysis of Fused Chlorides

Electrolysis is an essential process used for extracting alkali metals like sodium and lithium from their chlorides. These metals cannot be extracted by chemical reduction due to their high reactivity even with reducing agents like carbon. In the electrolysis process, molten or fused chlorides serve as the medium, which prevents interaction with atmospheric oxygen and thus oxidation.
During electrolysis, the metal ions move to the cathode where they gain electrons and transform into pure metal, while chlorine gas is released at the anode. This technique allows the extraction of alkali metals in their elemental form efficiently.

• Fused chlorides have relatively high melting points, which help in electrolyzing without further oxidation.
• Chlorine produced during this process is often captured and used industrially.

This method plays a significant role especially because of the high demand for pure reactive metals in various applications and the necessity of avoiding their oxidation during preparation.

Comparison of Sodium and Potassium

Sodium and potassium both belong to the alkali metal group but differ significantly in their practical applications. Sodium is favored over potassium due to several reasons. Firstly, sodium is found abundantly in nature in forms like sodium chloride (common salt), making it more cost-effective.
Secondly, sodium is less reactive with water compared to potassium, which reacts vigorously, even explosively, with water, posing safety risks in its handling and usage.
Furthermore, sodium's properties make it suitable for use in diverse industries. For instance:

• It acts as a crucial component in the manufacture of glass and detergents.
• Its role as a heat exchanger fluid is pivotal in nuclear reactors.
• Sodium vapor lamps benefit from its luminous efficiency, providing bright street lighting.

Meanwhile, potassium finds limited application—primarily in agriculture as a fertilizer component—due to its higher reactivity and lesser abundance, making sodium often more versatile and widely applied.