Question

Sodium bicarbonate solution has ${{p}{H}}$ less than 7. State true or false
A) True
B) False
C) Cannot be determined
D) None of the above.

Answer 1

Sodium bicarbonate is also called baking soda and is amphoteric in nature. ${{p}{H}}$ Value range is between 0-14, where 0-7 value is for acid, 7-14 is for basic compound and t with ${{p}{H}}$ 7 will be called as neutral.

Complete step by step solution:
Here we have to state whether $NaHC{{O}_{3}}$ possess a value of ${{p}{H}}$ less than 7, which is indicating that $NaHC{{O}_{3}}$ is acid or not.
We know that $NaHC{{O}_{3}}$, is amphoteric in nature i.e. it has a capability of behaving as acid and as well as nature.
For giving this statement an evidence let’s see two reactions,
$NaHC{{O}_{3}}+{{H}_{2}}S{{O}_{4}}\to N{{a}_{2}}S{{O}_{4}}+2{{H}_{2}}O+2C{{O}_{2}}$
Here as we know, ${{H}_{2}}S{{O}_{4}}$ is one of the most strong acid and , here $NaHC{{O}_{3}}$ reacts vigorously with ${{H}_{2}}S{{O}_{4}}$ through evolving $C{{O}_{2}}$ gas as the reaction product in this reaction and sodium sulphate is formed along with water.
Only the base, gives such type of reaction by donating hydroxyl ion ($O{{H}^{-}}$), so here $NaHC{{O}_{3}}$ is acting as the base and the other one is acid.
But in the reaction given below,
$NaHC{{O}_{3}}+NaOH\to N{{a}_{2}}C{{O}_{3}}+{{H}_{2}}O$
$NaHC{{O}_{3}}$ Is acting as an acid. The NaOH is one of the strongest bases and it will react with only the acid to give the type of reaction given above.
So here $NaHC{{O}_{3}}$, is furnishing ${{H}^{+}}$ ions in the reaction mixture, and behaving as an acid.
But the prominent reaction is as the weak base .And the ${{p}{H}}$ of the solution is determined through a digital ${{p}{H}}$ meter which gives the ${{p}{H}}$ value of the solution.
And we already have a ${{p}{H}}$ value for $NaHC{{O}_{3}}$, which is set by testing 0.1 molar aqueous solution of $NaHC{{O}_{3}}$ at ${{77}^{\circ }}F$, and we obtained a value between 8-9,which indicates that $NaHC{{O}_{3}}$ is a weak base.
So we can conclude that the above given statement is not true.

The correct option for the question is option (B).

Note: As we define $NaHC{{O}_{3}}$ as monosodium salt of carbonic acid which possess the alkalizing property, we usually consider $NaHC{{O}_{3}}$ as a weak acid, but it is having a ${{p}^{H}}$ range that is for bases.
$NaHC{{O}_{3}}$ on ionization yields the sodium and bicarbonate ion. Bicarbonate ion in the presence of acid medium decomposes to $C{{O}_{2}}$ and ${{H}_{2}}O$
$NaHC{{O}_{3}}\to N{{a}^{+}}+HC{{O}_{3}}^{-}$
$HC{{O}_{3}}^{-}+{{H}^{+}}\to C{{O}_{2}}+{{H}_{2}}O$