Question

Correct order of hydrolysis is: (a) \(\mathrm{PCl}_{5}<\mathrm{A} 1 \mathrm{Cl}_{3}<\mathrm{CCl}_{4}<\mathrm{SiCl}_{4}\) (b) \(\mathrm{CCl}_{4}<\mathrm{AlCl}_{3}<\mathrm{SiCl}_{4}<\mathrm{PCl}_{5}\) (c) \(\mathrm{AICl}_{3}<\mathrm{PCl}_{3}<\mathrm{CCl}_{4}<\mathrm{SiCl}_{4}\) (d) \(\mathrm{CCl}_{4}<\mathrm{AICl}_{3}<\mathrm{PCl}_{5}<\mathrm{SiCl}_{4}\)

Short answer

The correct order of hydrolysis is option (d): \( ext{CCl}_4 < ext{AlCl}_3 < ext{PCl}_5 < ext{SiCl}_4 \).

Step-by-step solution

Understanding Hydrolysis

Hydrolysis is a chemical reaction that involves the interaction of water with a compound. Typically in metal chlorides like \( ext{SiCl}_4 \) or \( ext{AlCl}_3 \), the metal can form a bond with the oxygen from water, causing the chlorine to be released and forming a hydroxide or an acid.

Analyzing Hydrolysis Tendency

The hydrolysis rate is influenced by the compound's structure, bonding, and the metal's ability to form stable products with water. Lewis acids like \( ext{AlCl}_3 \) or \( ext{SiCl}_4 \) tend to hydrolyze easily because they readily accept the lone pair of electrons from water.

Comparing Compounds

\( ext{CCl}_4 \) does not undergo hydrolysis due to the absence of empty orbitals, making it very stable and least reactive. \( ext{AlCl}_3 \) and \( ext{SiCl}_4 \) undergo hydrolysis due to their ability to form stronger bonds with oxygen, while \( ext{PCl}_5 \) hydrolyzes slowly as it partly forms \( ext{POCl}_3 \) first.

Correct Order of Hydrolysis

Based on the ease of hydrolysis, the order generally is from less reactive to more reactive: \( ext{CCl}_4 < ext{AlCl}_3 < ext{PCl}_5 < ext{SiCl}_4 \). \( ext{SiCl}_4 \) has the ability to form the Si-O bond most readily, making it the fastest to hydrolyze.

Key concepts

Chemical Reactivity

Chemical reactivity is a measure of how readily a substance undergoes a chemical reaction. In the context of hydrolysis, it indicates how easily a compound reacts with water. The structure of the molecule, including the types of bonds and the presence of functional groups, plays a significant role in determining reactivity.
- **Stable Compounds**: Compounds with strong covalent bonds or stable electronic configurations tend to be less reactive.
- **Reactive Compounds**: Compounds that can easily form new bonds, such as those with empty orbitals or positive charge centers, are more reactive.
For example, carbon tetrachloride (\(\mathrm{CCl}_4\)) does not hydrolyze easily due to its stable tetrahedral structure with no empty orbitals. In contrast, compounds like silicon tetrachloride (\(\mathrm{SiCl}_4\)) are highly reactive, making them more susceptible to hydrolysis.

Lewis Acids

Lewis acids are chemical species that have the ability to accept a pair of electrons, often due to having an empty orbital. They are crucial in many reactions, including hydrolysis of metal chlorides.
- **Characteristics**: A typical Lewis acid often has less than a full octet and a positive or neutral charge that creates an electron-deficient center.
- **Example in Hydrolysis**: Aluminium chloride (\(\mathrm{AlCl}_3\)) is a potent Lewis acid because it can easily accept electron pairs from water molecules during hydrolysis. This tendency makes \(\mathrm{AlCl}_3\) more reactive compared to organic compounds like \(\mathrm{CCl}_4\).
The role of Lewis acids can be crucial in understanding which compounds will hydrolyze more rapidly, driven by their need to achieve a stable electronic configuration.

Metal Chlorides

Metal chlorides are compounds composed of a metal and chlorine. Their interaction with water varies depending on their molecular structure and the properties of the metal.
- **Hydrolyzing Capability**: Metal chlorides with metals that readily accept oxygen atoms in their structure, such as silicons and aluminums, are more prone to hydrolysis.
- **Example Analysis**: \(\mathrm{SiCl}_4\) hydrolyzes rapidly due to silicon's ability to form strong bonds with oxygen. Meanwhile, \(\mathrm{CCl}_4\), having no such metallic bond character and empty orbitals, remains unreactive with water.
Understanding the nature of metal chlorides helps predict their reactivity patterns, especially in educational settings where knowing the order of hydrolysis can enhance comprehension of chemical behaviors.

Hydrolysis Reaction

Hydrolysis is a type of chemical reaction wherein a molecule is split into two parts through the addition of water. This reaction is essential for understanding the behavior of many inorganic compounds.
- **Mechanism**: During hydrolysis, a bond in the reacting compound is cleaved, and a water molecule splits, usually into hydrogen cations and hydroxide anions. This process involves the attacking of electron-deficient sites of the compounds.
- **Importance in Metal Chlorides**: The hydrolysis of metal chlorides like \(\mathrm{SiCl}_4\) results in the formation of silicon dioxide and hydrochloric acid. Such reactions are not only fascinating but also pivotal in industrial applications.
Knowing how hydrolysis works can help in predicting the resultant products and the order of reactivity among various metal chlorides, which is fundamental in both academic and practical chemical contexts.