is Na2O an alkali or not? cos an an alkali is a soluble base so
is NaOH an alkali along with Na2O im veey confused with it. pls
help me clarify what is what
An alkali ( noun ) is any solution ( adjective : "alkaline
solution" ) which contains a higher concentration of OH- ions over
H+ ions.
Bases which are able to undergo hydrolysis ( hydrolysis =
"chemical reaction with water" ) to generate soluble
products are called "soluble bases" because the solid base
appears to dissolve in water (it is really undergoing a chemical
reaction with water, ie. hydrolysis, to generate soluble
products).
For instance, Na2O or sodium oxide, contains the strongly basic
O2- dinegative oxide ion, which in a bid to stabilize itself,
abstracts protons H+ ions from water, generating 2OH- ions.
O2- + H2O ---> 2OH-
Since NaOH is soluble (unlike say, MgO), the resulting solution
is alkaline, ie. has a higher concentration of OH- ions over H+
ions, and has pH greater than 7 (note that pH = 7 holds true for
neutral solutions (only) at 25 deg C; therefore at 25 deg C, any pH
greater than 7 is considered alkaline).
There are 3 different definitions of acids (and therefore,
of bases). These are : Bronsted-Lowry, Lewis and Arrhenius.
For 'O' levels, the Arrhenius definition "an acid dissolves in
water to generate H+ ions" is often used, even though the
other two definitions (Bronsted-Lowry and Lewis), used at 'A'
levels, are more correct and useful.
To summarize :
A (Bronsted-Lowry) base is any species that accepts protons H+
ions. A 'soluble' base undergoes hydrolysis ('chemical reaction
with water') to generate a solution containing a higher
concentration of hydroxide OH- ions over protons H+ ions, which is
called an "alkali" or "alkali solution" or
"alkaline solution".