Hydrides
Chapter Name : Hydrogen |
Sub Topic Code : 102_11_09_05_01 |
Topic Name : Hydrides |
|
Sub Topic Name : Ionic Or Saline Hydrides |
|
Introduction
Hydrides are formed by those metals whose electronegativity values are appreciably lower than that of hydrogen.
Most of the s-block metals form this type of hydrides. These are non-volatile, non-conducting crystalline solids. However, BeH2 and MgH2 have covalent polymeric structure. These ionic hydrides have rock-salt structure.
Pre-Requisites:
Saline hydrides, reducing agent
Activity:
Electrolysis of solution of saline hydride in molten alkali halide produces H2 at anode. Saline hydrides react explosively with water.
NaH(s) + H2O(aq) ? NaOH(aq) + H2(g)
The fire so
produced cannot be extinguished by CO2 as it gets reduced by
the hot metal hydride. Only sand is useful, as it is a solid.
Real Life Question:
Does hydrogen combine with any other element except for oxygen
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Saline hydrides | Ionic or saline hydride, is a hydrogen atom bound to an extremely electropositive metal, generally an alkali metal or alkaline earth metal. |
| Reducing agent | Combustibility is a measure of how easily a substance will set on fire, through fire or combustion. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| Water, drain clog removal (containing sodium hydroxide) + aluminium foil | When water is added to a drain clog removal liquid in the presence of aluminium ( using aluminium foil) , hydrogen gas is liberated. This is an exothermic reaction. |
Real life uses :
Alkali metal hydrides are used for making LiAlH4, NaBH4 etc.
Alkali metal hydrides are also used for the removal of last traces of water
from organic compounds.
Places to visit :
Chemistry
lab
Practical examples around us
| Examples | Explainations |
|---|---|
| Hydrogen as a fuel | Hydrogen is commonly used in the petroleum and chemical industries and is also widely used for many physics and engineering applications such as welding or as a coolant. |
What you learn in Theory:
These hydrides are formed by the transfer of
electrons from the metals to the hydrogen atoms and thus contain hydride ion, H-.
For example lithium hydride Li+H- and calcium hydride, Ca2+
(H-)2.
What you learn in Practice:
·
These are white crystalline solids and
their crystal structures consist of ions.
They have high melting and boiling points and
conduct electricity in the fused state, liberating dihydrogen at the anode.