- No.iv. How can you justify that NH3 is Bronsted-Lowry-base but not Arrhenius base?
Answer. According to Arrhenius concept, bases are only those compounds which contain (OH–) ions. As NH3 does not contain any (OH–) ion therefore, it is not an Arrhenius base. While Bronsted Lowry base is a substance that can accept a proton (H+) from another substance. For example, NH3 accepts a proton from water such as
H2O(1) + NH3(aq) NH4+(aq) +
As NH3 can accept a proton so it is a Bronsted-Lowry base.
- No. v. State and explain the neutralization reaction according to Lewis concept.
Answer. According to Lewis concept neutralization reaction is donation and acceptance of an electron pair to form a coordinate covalent bond in adduct. Adduct is a single specie product of any Lewis acid-base reaction. For example, formation of ammonium ion is a neutralization reaction between H+ (Lewis acid) and NH3 (Lewis base).
H++NH3 [H NH3] +
- No.vi. Define and give the characteristics of a Lewis acid.
Answer. According to Lewis concept an acid is a substance (molecule or ion) which can accept a pair of electrons. For example, BF3, H+
According to this concept, the following species can act as Lewis acids:
- Molecules in which the central atom has incomplete octet. For example, in BF3, AlCl3, FeCl3, the central atom has only six electrons around it; therefore, these can accept an electron pair.
- Simple cations can act as Lewis acids. All cations act as Lewis acids since they are deficient in electrons. However, cations such as Na+, K+, Ca2+ ions, etc., have a very little tendency to accept electrons. While the cations like H+, Ag+ ions, etc., have a greater electron accepting tendency therefore, act as Lewis acids