Chemistry Class 11 NCERT Solutions: Chapter 9 Hydrogen Part 3

Q: 10. Do you expect the carbon hydrides of the type Equation to act as ‘Lewis’ acid or base? Justify your answer:

Answer:

For carbon hydrides of type Equation , the following hydrides are possible for

Equation

Equation

Equation

For a hydride to act as a Lewis acid i.e., electron accepting, it should be electron- deficient. Also, for it to act as a Lewis base i.e., electron donating, it should be electron-rich.

Taking Equation as an example, the total number of electrons are 14 and the total covalent bonds are seven. Hence, the bonds are regular Equation centered bonds.

Q 10 Hydride C2 H6 has Sufficient Electrons to be Represented by a Conventional Lewis Structure

Hydride Has Sufficient Electrons for Lewis Structure

Q 10 Hydride C2 H6 has Sufficient Electrons to be Represented by a Conventional Lewis Structure

Hence, hydride Equation has sufficient electrons to be represented by a conventional Lewis structure. Therefore, it is an electron-precise hydride, having all atoms with complete octets. Thus, it can neither donate nor accept electrons to act as a Lewis acid or Lewis base.

Q: 11. What do you understand by the term “non-stoichiometric hydrides”? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Answer:

Non-Stoichiometric hydrides are hydrogen-deficient compounds formed by the reaction of dihydrogen with d-block and f-block elements. These hydrides do not follow the law of constant composition. For example: Equation etc.

Alkali metals form stoichiometric hydrides. These hydrides are ionic in nature. Hydride ions have comparable sizes Equation with alkali metal ions. Hence, strong binding forces exist between the constituting metal and hydride ion. As a result, stoichiometric hydrides are formed. Alkali metals will not form non-stoichiometric hydrides.

Q: 12. How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

Answer:

Metallic hydrides are hydrogen deficient, i.e., they do not hold the law of constant composition. It has been established that in the hydrides of Ni, Pd, Ce, and Ac, hydrogen occupies the interstitial position in lattices allowing further absorption of hydrogen on these metals. Metals like Pd, Pt, etc. have the capacity to accommodate a large volume of hydrogen. Therefore, they are used for the storage of hydrogen and serve as a source of energy.

Q: 13. How does the atomic hydrogen or oxy-hydrogen torch function for cutting and welding purposes? Explain.

Answer:

Atomic hydrogen atoms are produced by the dissociation of dihydrogen with the help of an electric arc. This releases a huge amount of energy Equation This energy can be used to generate a temperature of 4000 K, which is ideal for welding and cutting metals. Hence, atomic hydrogen or oxy-hydrogen torches are used for these purposes. For this reason, atomic hydrogen is allowed to recombine on the surface to be welded to generate the desired temperature.

Q: 14. Among Equation and HF, which would you expect to have highest magnitude of hydrogen bonding and why?

Answer:

The extent of hydrogen bonding depends upon electronegativity and the number of hydrogen atoms available for bonding. Among nitrogen, fluorine, and oxygen, the increasing order of their electronegativities are Equation . Hence, the expected order of the extent of hydrogen bonding is Equation . But, the actual order is Equation

Although fluorine is more electronegative than oxygen, the extent of hydrogen bonding is higher in water. There is a shortage of hydrogens in HF, whereas there are exactly the right numbers of hydrogens in water. As a result, only straight chain bonding takes place. 0n the other hand, oxygen forms a huge ring-like structure through its high ability of hydrogen bonding.

In case of ammonia, the extent of hydrogen bonding is limited because nitrogen has only one lone pair. Therefore, it cannot satisfy all hydrogens.

Q 11 The Extent of Hydrogen Bonding is Limited Because Nitrogen has Only one Lone Pair

Hydrogen Bonding Is Limited

Q 11 The Extent of Hydrogen Bonding is Limited Because Nitrogen has Only one Lone Pair

Q: 15. Saline hydrides are known to react with water violently producing fire. Can Equation , a well-known fire extinguisher, be used in this case? Explain.

Answer

Saline hydrides (i.e., Equation , etc.) react with water to form a base and hydrogen gas. The chemical equation used to represent the reaction can be written as:

Equation

The reaction is violent and produces fire.

Equation is heavier than dioxygen. It is used as a fire extinguisher because it covers the fire as a blanket and inhibits the supply of dioxygen, thereby dousing the fire. Equation can be used in the present case as well. It is heavier than dihydrogen and will be effective in isolating the burning surface from dihydrogen and dioxygen.

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