Question #9ac80

2 Answers
Jun 13, 2017

Answer:

Alkalis are water soluble bases.

Explanation:

Sodium hydroxide dissolved in water forms #NaOH(aq)# which is an alkali. Something like calcium hydroxide is not water soluble would be described as a base.

So both bases and alkalis react with acids and neutralise them, but only alkalis are water soluble. All alkalis are basic but not all bases are alkalis.

Jun 13, 2017

Answer:

In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water.

Explanation:

Not all bases are alkalis. The most general definition is a Lewis Base, which is any compound that can accept a proton. #OH^-# ions do not necessarily need to be involved. In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons.

A Lewis acid is therefore any substance, such as the #H^+# ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the #OH^-# ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor.

The Lewis acid-base theory explains why #BF_3# reacts with ammonia. #BF_3# is a trigonal-planar molecule because electrons can be found in only three places in the valence shell of the boron atom. As a result, the boron atom is #sp^2# hybridized, which leaves an empty #2pz# orbital on the boron atom. #BF_3# can therefore act as an electron-pair acceptor, or Lewis acid.

It can use the empty #2pz# orbital to pick up a pair of nonbonding electrons from a Lewis base to form a covalent bond. #BF_3# therefore reacts with Lewis bases such as #NH_3# to form acid-base complexes in which all of the atoms have a filled shell of valence electrons.

The Lewis acid-base theory can also be used to explain why nonmetal oxides such as #CO_2# dissolve in water to form acids, such as carbonic acid #H_2CO_3#.

#CO_2#(g) + #H_2O# -> #H_2CO_3#(aq)

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch11/lewis.php