Question

Identify the false statement about the extraction of alkali metals. (1) They cannot be extracted by thermal decomposition because their compounds are stable. (2) They cannot be extracted by chemical reduction because they themselves are strong reducing agents. (3) They cannot be extracted by clectrolysis of their aqueous solutions of salts becausc they arc morc clectropositive than the hydrogen (4) They cannot be extracted by clectrolysis of the fuscd salts becausc of thcir high melting points.

Short answer

Statement (4) is false. Alkali metals can be extracted by electrolysis of their fused salts.

Step-by-step solution

Understand the nature of alkali metals

Alkali metals are highly reactive and are usually found in nature in compound form rather than in their pure state.

Analyze statement (1)

Alkali metals cannot be extracted by thermal decomposition because their compounds are stable under high temperatures.

Analyze statement (2)

Alkali metals cannot be extracted by chemical reduction because they are strong reducing agents themselves, which makes it difficult to find another substance that can reduce them.

Analyze statement (3)

They cannot be extracted by electrolysis of their aqueous solutions of salts because they are more electropositive than hydrogen. This means in an aqueous solution, they would cause the formation of hydrogen gas instead of releasing the metal.

Analyze statement (4)

The statement claims that alkali metals cannot be extracted by electrolysis of their fused salts because of their high melting points. This is incorrect. While they have high melting points, electrolysis of fused salts is still the standard method used to extract alkali metals.

Key concepts

chemical reduction

In chemistry, the process of chemical reduction involves the gain of electrons by one of the atoms involved in the reaction. For alkali metals, they themselves are strong reducing agents. This means they readily lose electrons and become oxidized. Because of this property, it is challenging to find a substance that can reduce them further. Therefore, chemical reduction is not viable for the extraction of alkali metals from their compounds. Instead, other methods like electrolysis are preferred, given the highly reactive nature of alkali metals.

electrolysis of fused salts

Electrolysis is a method of using a direct electric current (DC) to drive a non-spontaneous chemical reaction. For alkali metals, electrolysis of fused salts is an effective extraction method. Despite their high melting points, fused salt electrolysis is commonly used to extract alkali metals.

The process involves heating the alkali metal compound until it melts and then passing an electric current through it. Electrolysis causes the alkali metal cations to migrate to and be reduced at the cathode (negative electrode), forming the pure metal. An example can be seen with sodium chloride (common table salt); when it is melted and subjected to electrolysis, it produces metallic sodium and chlorine gas.

stability of alkali metal compounds

Alkali metal compounds are known for their stability, especially under high temperatures. This stability makes thermal decomposition an ineffective method for extracting alkali metals because their compounds do not easily decompose when heated.

For example, compounds like sodium chloride or potassium chloride have high melting and boiling points, meaning they remain stable and do not break down into simpler substances under heat alone. This is why alternative processes like electrolysis are necessary to successfully extract alkali metals from their stable compounds.

electropositive nature

Electropositivity refers to the ability of an element to donate electrons and form positive ions (cations). Alkali metals are highly electropositive. This characteristic means they easily lose their single valence electron to form ions.

Due to their electropositive nature, alkali metals are more likely to form ionic bonds and react vigorously. When trying to extract them from an aqueous solution of their salts through electrolysis, instead of the metal being deposited, hydrogen is usually released. This is because alkali metals are more electropositive than hydrogen, leading to the reduction of water to form hydrogen gas rather than the metal.