Q1. Why an ice cube floats on water?
Ice cube floats on water as density of ice is less than that of water.
Q2. Discuss the amphoteric nature of water.
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.
Q3. Comment on any one laboratory method of preparation of dihydrogen?
Dihydrogen is prepared by the reaction of granulated zinc with dihydrochloric acid.
Q4. What is the reaction of dihydrogen with metals?
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.
Q5. Give an example of electron deficient molecular hydride.
Example of electron deficient molecular hydride is diborane (B2H6).
Q6. How hydrogen resembles alkali metals and halogens?
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.
Q7. Discuss the structure of water.
In the gas phase water is a bent molecule with a bond angle of 104.5o, and an 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 hexagonal form, but at low temperature, it condenses to cubic form.
Q8. What happens when dihydrogen reacts with halogens?
Dihydrogen reacts with halogens X2 to give hydrogen halides, HX.
Q9. Why H+ ion does not exist freely?
When a hydrogen atom loses an electron it results in a 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.