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Q1. What is the reaction of dihydrogen with metals?

Solution

With metals it combines at a high temperature to yield the corresponding hydrides.  H₂ (g)  +  2M (g)  ----->  2MH (s) , where M is an alkali metal. 

Q2. 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.

Q3. Why an ice cube floats on water?

Solution

Ice cube floats on water as density of ice is less than that of water.

Q4. 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.                                    

Q5. Discuss the amphoteric nature of water.

Solution

The water molecule has the ability to act as an acid as well as a base, i.e. it behaves as an amphoteric substance, like it acts as an acid with ammonia and as a base with H₂S.

Q6. 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.

Q7. Give an example of electron deficient molecular hydride.

Solution

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

Q8. What happens when dihydrogen reacts with halogens?

Solution

Dihydrogen reacts  with halogens X₂ to give hydrogen halides, HX.

Q9. Comment on any one laboratory method of preparation of dihydrogen?

Solution

Dihydrogen is prepared by the reaction of granulated zinc with dihydrochloric acid.