Question

Which of the following pairs of the substance cannot exist together in solution?
A.${\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}{\text{ + NaOH}}$
B.${\text{NaHC}}{{\text{O}}_{\text{3}}}{\text{ + N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$
C.${\text{NaHC}}{{\text{O}}_{\text{3}}} + {\text{NaOH}}$
D.${\text{NaOH + NaCl}}$

Answer 1

Neutralisation reaction: The reaction between acid and base to form the salt and water is known as neutralisation reaction. For example: the reaction of sodium hydroxide and hydrochloric acid to form sodium chloride and water.

Complete step by step solution:
First of all we will discuss acids, bases and amphoteric compounds.
Acids: Those compounds which on ionization produce ${H^ + }$ions, are known as acids. They are sour in taste. Acids change the color of litmus from blue to red. When they react with bases then they become less acidic.
Bases: Those compounds which on ionization produce $O{H^ - }$ions, are known as bases. They are slippery in nature. Bases change the color of litmus from red to blue. When they react with acids then they become less basic.
Amphoteric Compounds: Those compounds which can react with both acids and bases are known as amphoteric compounds.
There are so many factors by which we can decide whether a compound or solution is acidic or basic.
pH values: If the pH value is in between $0 - 7$then the solution or compound will be acidic in nature and If the pH value is in between $7 - 14$then the solution or compound will be basic in nature. And if the pH value is exactly seven then compound or solution will be neutral i.e. neither acidic nor basic in nature.
Electron pair acceptor and donor: This concept was given by Lewis. According to Lewis: Lewis acids are those substances or solutions which can accept electron pairs and Lewis bases are those substances or solutions which can donate electron pairs.
Arrhenius concept: According to Arrhenius: Acids are those compounds or solutions which can give hydrogen ion or hydronium ion in water and bases are those compounds or solutions which can take hydrogen ion or hydronium ion in water.
Bronsted-Lowry concept: This was based on the proton acceptor and proton donor. If a compound or solution is a proton donor then it is known as acids and if the solution or compounds are proton acceptor then it is known as bases.
So, if we summarise all these then we can define acids and bases as:
Acids: Those compounds or solutions which can give hydronium ion or proton donor or electron pair acceptors and have pH range $0 - 7$, are known as acids.
Bases: Those compounds or solutions which are proton acceptor, can accept hydrogen ion or give hydroxide ion, or electron pair donor and have pH range $7 - 14$, are known as bases.
Now in the question in option A we are given with ${\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}{\text{ + NaOH}}$ which are salt and base so they can exists together. In option B we are given with ${\text{NaHC}}{{\text{O}}_{\text{3}}}{\text{ + N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}$ which are acid and salt so they can exists together. In option C we are given with ${\text{NaHC}}{{\text{O}}_{\text{3}}} + {\text{NaOH}}$which are acid and base. Hence they cannot exist together in a solution; they react with each other and form sodium carbonate and water. ${\text{NaHC}}{{\text{O}}_{\text{3}}} + {\text{NaOH}} \to {\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O}}$. In option D we are given with ${\text{NaOH + NaCl}}$ which are base and salt so they can exist together.
Hence the pair which cannot exists in the solution is ${\text{NaHC}}{{\text{O}}_{\text{3}}} + {\text{NaOH}}$.

So option C is correct.

Note: Amphoteric Compounds: Those compounds which can act as both acids as well as bases are known as amphoteric compounds. For example: water. Water can release hydrogen ions so can act as acid as well as can give hydroxide ions so can act as base. Hence water is an example of amphoteric.