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9.19  Consider the reaction of water with F2 and suggest, in terms of oxidation and reduction, which species are oxidized/reduced.

Answer-  The reaction of fluorine with water-  -----------reduction (O.N of F changes from 0 to -1)    ------------- Oxidation( O.N of O changes from -2 to 0) Fluorine reduced by gaining an electron and water oxidized by losing an electron.

9.18 What do you understand by the term ’auto-protolysis’ of water? What is its significance?

Answer-  It means water molecules can react with each other and form hydronium ion and hydroxide ion. (self-ionization) it indicates its amphoteric nature; means behave as acid as well as the base. the Hydronium Ion - conjugate acid  the hydroxide ion - conjugate base

9.17  Compare the structures of H2O and H2O2.

Answer-  In the gaseous phase water is a bent molecule with a bond angle of 104.5 degree, and O-H bond length of 95.7 pm. It is a highly polar molecule. Hydrogen peroxide has a non-planner structure both in the gas phase and solid phase. The dihedral angle in the gas phase is 115.5 degree and in the solid phase is 90.2 degree. fig-

Arrange the following  $NaH, MgH_2,$ and $H_2O$ in order of increasing reducing property

Answer- increasing order of reducing property-   Na can easily donate electrons so it has a higher reducing property. Both   are covalent hydrides. water has less reducing property because it has high bond dissociation energy than

9.16 arrange the following

(iii) H–H, D–D and F–F in order of increasing bond dissociation enthalpy

Answer-   increasing order of bond dissociation enthalpy In F-F high repulsion force is acting so breaking should be easy. while in case of H-H and D-D, bond pair of D-D is more strongly attracted by the nucleus because of the higher nucleus mass in D2. we know that higher the attraction high is the bond strength.

9.16 Arrange the following

(ii) LiH, NaH and CsH in order of increasing ionic character

Answer- the increasing order of ionic character - The ionic character can be measured by the electronegativity difference between the atom. we know that down the group electronegativity decreases. Therefore, Cs has most electronegative character then Na then Li.

9.16  Arrange the following

(i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance

Answer- increasing order of electrical conductance- electrical conductivity depends on its ionic nature. more is the ionic more is the conductivity. Berrium hydride is covalent in nature so it has least conductivity. Titanium hydride is metallic in nature so it will also conduct. we also know that greater is the size of cation more is the ionic in nature.

9.15  Saline hydrides are known to react with water violently producing fire. Can CO2, a well-known fire extinguisher, be used in this case? Explain.

9.14 Among NH3, H2O and HF, which would you expect to have highest magnitude of hydrogen bonding and why?

Answer- The strength of hydrogen bonding depends on the electronegativity of an atom electronegativity order  The expected order should be  But the  actual order is  This is because of the extent of H bonding in a water molecule is more due to the presence of one extra hydrogen atom. Also, Oxygen atom forms a huge ring like structure through its high ability of hydrogen bonding

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

Answer- Atomic hydrogen can be prepared by dissociation of a bond of dihydrogen with the help of an electric arc. This release a huge amount of energy around 135 kJ/mol and this energy can be used to generate a high temperature of 4000K,  which is desirable for welding and cutting of metals. Therefore, atomic hydrogen or oxy-hydrogen torch are used for welding purpose.

9.12  How do you expect the metallic hydrides to be useful for hydrogen storage? Explain

Answer- Metallic hydrides are hydrogen deficient and they don't hold the law of constant composition.it is established that hydrides of nickel, palladium, and Ce have lattice different where hydrogen occupies the interstitial position in the lattices allowing further absorption of hydrogen on these metals. Some of the metals like Pd and Pt accommodate a very large volume of hydrogen and...

9.11  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. they are formed by d & f block elements. Such hydrides do not follow the law of constant composition.  Examples-  etc. Alkali metals do not form these types of hydrides. Alkali metals form stoichiometric hydrides. These hydrides are ionic in nature.

9.1o  Do you expect the carbon hydrides of the type (CnH2n + 2) to act as ‘Lewis’ acid or base? Justify your answer.

Answer- the general term   for n = 1, 2, 3.. we get   ... Lewis acids are an electron acceptor, So the above compound should be electron deficient species.   taking an example Here we can directly count that both the Carbon atom has perfect 8 electrons in sharing. they follow the octet rule. It is electron precise hydride and it neither donate or accept electrons to act Lewis acid or base

9.9  What characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactions

Answer- Electron-deficient hydrides do not have required electrons to form a regular bond in which two electrons are shared by two atoms. e.g.  etc Because of electron deficiency, they have the tendency to accept electrons. hence they act as Lewis acid.

9.8  What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen? Provide justification with suitable examples.

ANswer- (i)Electron-deficient hydrides-  Those compounds having fewer electrons to writing its conventional Lewis structure. examples  (all the elements of group 13 form electron deficient hydrides) (ii)Electron-precise hydrides- Those compounds have the required number of electrons to write their conventional Lewis structure. ex-  (all elements of group 14 form such...

9.7  Discuss the consequences of high enthalpy of H–H bond in terms of chemical reactivity of dihydrogen?

Answer- The ionization enthalpy of the H-H bond is very high (1312kJ/mol). It means hydrogen has less tendency to form  ions. Its ionization enthalpy is comparable to halogens. Hence it forms a diatomic molecule, hydrides with the elements, and a large number of covalent bonds. It does not possess any metallic character like metals

9.6 Complete the following reactions

$\\(i)H_{2}(g)+MmOo(s)\rightarrow \\ (ii)CO(g)+H_{2}(g)\rightarrow \\ (iii)C_{3}H_{8}(g)+3H_{2}O(g)\rightarrow\\ (iv)Zn(s)+NaOH(aq)\rightarrow$

9.5  Describe the bulk preparation of dihydrogen by an electrolytic method. What is the role of an electrolyte in this process?

Answer- The dihydrogen is prepared by electrolysis of acidified water using platinum electrodes. generally acid is sulphuric acid and base is sodium hydroxide is used. Role of electrolyte- The electrical conductivity of pure water is very low due to the absence of ions in it. Hence electrolysis of water takes place at slow rate. If we add an electrolyte as an acid or base it will increase the...

9.4 How can the production of dihydrogen, obtained from ‘coal gasification’, be increased?

Answer-  The process of producing syngas from coal is known as 'coal gasification' The production of dihydrogen can be increased by reacting carbon monoxide of syngas mixture with the steam in the presence of iron chromate as a catalyst. This is called 'water gas shift reaction'. carbon dioxide can be removed by scrubbing with a sodium solution.

9.3 Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions ?

Answer- Ionisation enthalpy of hydrogen is quite high(1312 kJ/mol). Hence it is very difficult to remove its only one electron. As a result, the tendency to exist in the monoatomic form is very low.
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