Question

Which of the properties of interstitial hydrides is correct? (a) They give rise to metals fit for fabrication (b) They generally form non-stoichiometric species (c) They can be used as hydrogenation catalysts (d) The hydrogen dissolved in titanium improves its mechanical properties.

Short answer

Option B is correct; interstitial hydrides are generally non-stoichiometric.

Step-by-step solution

Understanding Interstitial Hydrides

Interstitial hydrides are formed when hydrogen atoms occupy the interstices (spaces) in the metal lattice without significantly affecting the metal structure.

Analyzing Option A

Option A states that hydrides give rise to metals fit for fabrication. Interstitial hydrides often possess metallic properties due to the retention of the metal lattice, allowing them to be useful in various ways, including applications in metallurgy.

Evaluating Non-Stoichiometric Nature

Option B mentions that interstitial hydrides generally form non-stoichiometric species. This is characteristic of interstitial hydrides as the hydrogen atoms occupy interstitial spaces irregularly.

Hydrogenation Catalyst Use

Option C states that they can be used as hydrogenation catalysts. Many transition metals, which form interstitial hydrides, can serve as catalysts in hydrogenation reactions because the absorbed hydrogen can revert to gaseous form, facilitating reactivity.

Improvement of Mechanical Properties by Hydrogen

Option D suggests hydrogen dissolved in titanium improves its mechanical properties. However, hydrogen can make metals brittle (known as hydrogen embrittlement), which can be detrimental to mechanical properties.

Conclusion by Elimination and Understanding

Option B is the correct property of interstitial hydrides, as they commonly display non-stoichiometric behavior, where the ratio of hydrogen to metal is not fixed.

Key concepts

Non-stoichiometric Species

Interstitial hydrides are often associated with non-stoichiometric species. This term refers to a situation where the proportion of elements in a compound does not adhere to a simple integer ratio. In interstitial hydrides, hydrogen atoms occupy spaces within a metal lattice but do not follow a strict ratio relative to the metal atoms. This irregular and variable occupancy results in the non-stoichiometric nature. Such hydrides, found in transition metals like titanium or palladium, can vary in hydrogen content depending on conditions like temperature and pressure. This variability can be useful in tailoring materials for specific engineering applications, especially where varying hydrogen contents can alter physical or chemical properties. The presence of non-stoichiometric species causes unpredictability in crystal structure and bonding. These shifts can lead to changes in properties such as electrical conductivity and magnetism, which are essential for various technological applications.

Metal Lattice

In interstitial hydrides, hydrogen atoms are incorporated into the metal lattice of host metals. A metal lattice is a three-dimensional, highly ordered structure where metal atoms share electrons, creating bonds that confer a metallic nature. The incorporation of hydrogen occurs in the spaces or interstices, which are small voids within this lattice. By occupying these interstices, hydrogen atoms do not radically alter the metallic structure. They are small enough to fit into these spaces without significantly disrupting the lattice, allowing the metal's inherent properties to remain largely intact. This process is crucial because it permits metals to retain their strength and ductility while gaining new functionalities. Such hydrides can thus maintain their metallic shine and conductivity. The metal lattice’s integrity is key for applications where preservation of the metal's original properties is needed, even as additional characteristics provided by hydrogen, like storage and catalytic abilities, are harnessed.

Hydrogenation Catalysts

Hydrogenation catalysts are crucial in a vast range of chemical reactions, particularly those involving the addition of hydrogen to other compounds. Interstitial hydrides, especially those involving transition metals, act as effective catalysts in hydrogenation reactions. The underlying process involves hydrogen atoms entering and leaving the metal lattice with relative ease. This ability facilitates the conversion of absorbed hydrogen into a reactive form that can readily engage in chemical reactions. Interstitial hydrides offer a large surface area for these reactions, enhancing their effectiveness as catalysts. Many industrial processes, like the production of margarine through the hydrogenation of vegetable oils, rely on such catalysts. Transition metals like nickel, palladium, and platinum are renowned for forming interstitial hydrides that perform exceptionally well in this context. These hydrides improve efficiency by lowering the energy required to initiate reactions, making them indispensable in a variety of chemical industries.