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Q1. What are ionic hydrides?

Solution

These are stoichiometric compounds of dihydrogen formed with most of the s-block elements which are highly electropositive in character. The ionic hydrides are crystalline and non-volatile and non-conducting in solid state.

Q2. Write the uses of dihydrogen.

Solution

The largest single use of dihydrogen is in the synthesis of ammonia that is used in the synthesis of nitric acid and in the nitrogenous fertilizers. Dihydrogen is used in the manufacture of vanaspati fat and in the manufacture of bulk organic chemicals like methanol. It is also used in the manufacture of hydrogen chloride and metal hydrides.

Q3. How the isotopes of hydrogen differ?

Solution

The isotopes of hydrogen differ from one another in respect of the presence of neutrons. Ordinary hydrogen, protium has no neutrons, deuterium has one and tritium has two neutrons in the nuclei.

Q4. Give an example of electron deficient molecular hydride.

Solution

Example of electron deficient molecular hydride is diborane (B₂H₆).

Q5. Give an example of interstitial water molecule.

Solution

An example of interstitial water molecule is BaCl₂.2H₂O.

Q6. Give example of electron-rich hydrides?

Solution

Example of electron-rich hydrides are the elements of group 15-17 form such compounds (NH₃ has one lone pair, water has two and HF has three lone pairs).

Q7. Discuss the structure of water.

Solution

In the gas phase water is a bent molecule with a bond angle of 104.5^o, and O-H bond length of 95.7pm. It is a highly polar molecule. In the liquid phase water molecules are associated together by hydrogen bonds. The crystalline form of water is ice. At atmospheric pressure ice crystallizes in the hexagonal form, but at low temperature it condenses to cubic form.                                    

Q8. Why H⁺ ion does not exist freely?

Solution

When hydrogen atom loses an electron it results in nucleus (H⁺) of 1.5 x 10^-3 pm size, which is very small as compared to normal atomic or ionic sizes. As a result H⁺ ion does not exist freely.

Q9. How hydrogen resembles alkali metals and halogens?

Solution

Hydrogen has an electronic configuration of 1s¹. Its electronic configuration is similar to the outer electronic configuration ns¹ of alkali metals which belong to the first group of the periodic table, and like halogens (with electronic configuration ns²np⁵ ) it is short by one electron to the corresponding noble gas configuration, helium 1s².

Q10. Explain the oxidising and reducing action of H₂O₂.

Solution

H₂O₂ acts as an oxidising as well as reducing agent in both acidic and alkaline media. (i)  Oxidising action in acidic medium 2Fe⁺²_(aq) + 2H⁺ _(aq) + H₂O_2(aq) → 2Fe⁺³   + 2H₂O _(l) PbS_(s) + 4H₂O_{2 (aq)} → PbSO_{4 (aq)} + 4H₂O_(l)   (ii)  Reducing action in acidic medium 2Fe⁺²_(aq) + H₂O_2(aq) →2Fe⁺³   + 2OH^- _(l) Mn⁺² + H₂O_2(aq)        → Mn⁺²  + 2OH^- _(l)