Question

The equivalent mass of phosphoric acid $${{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}}$$is 49. It behaves as _________ acid.
A. Monobasic
B. Dibasic
C. Tribasic
D. Tetrabasic

Answer 1

Hint: Monobasic acid is defined as those acids which contain only one replaceable hydrogen in it. The dibasic acid is that which contains two replaceable hydrogen in it. The tribasic acid is one which has three replaceable hydrogen in it and tetrabasic is that which has four replaceable hydrogen in it.

Complete step by step answer:
The formula for determining the equivalent is the division of the molecular weight of the compound by its valency factor. The formula is expressed as the following: equivalent weight = $$\dfrac{{98}}{{49}}$$
So let us first find the molecular weight of the compound. The atomic weight of hydrogen is 1 and here we have 3 hydrogen so it will be three times 1 that is 3. The atomic weight of phosphorus is 31. The atomic weight of oxygen is 16. There are 4 atoms of oxygen so it will be 4 times of 16 that is 64. Now let us add them all
Molecular weight = $$3 + 31 + 64 = 98{\text{gmo}}{{\text{l}}^{{\text{ - 1}}}}$$
The equivalent weight is equal to 49$$gmo{l^{ - 1}}$$
The replaceable hydrogen $$\dfrac{{98}}{{number\; of\; replaceable \;hydrogen}}$$ number will tell the nature of the acid. If it comes 1 then it is monobasic, if it comes two then dibasic and so on. So now let us substitute the values in the formula:
49 = $$\dfrac{{98}}{{number\; of\; replaceable\; hydrogen}}$$
Number Of replaceable hydrogen = 2
So as the number of replaceable hydrogen is 2 so it will be dibasic acid.

So, the correct answer is Option B.

Note: The other name of phosphoric acid is orthophosphoric acid. It is used in the manufacturing of fertilizers. It is also used in dental cements and albumin derivatives. It is widely used in textile and sugar industries.