Question

The normality of orthophosphoric acid having purity of $70\%$ by weight and specific gravity $1.54$ is:
A. $11N$
B. $22N$
C. $33N$
D. $44N$

Answer 1

Normality is the number of gram or mole equivalents of solute present in one litre of solution. It can be found by first calculating density and then using gram equivalents and volume to find normality.

Complete step by step answer:
Orthophosphoric acid is also known as Phosphoric acid has chemical formula ${H_3}P{O_4}$ and is a weak base. It is purely found as colourless solid but normally is a colourless syrup of $85\%$ concentration in water. Starting with the calculations, first we will start with finding the density of orthophosphoric acid.
Normality is described as the number of gram or mole equivalents of solute present in one litre of solution. It is the measure of reactive capacity of a molecule.
$Density = Specific \, Gravity \times density\, of\, water$
Here, specific gravity is the ratio of the density of an object and a reference substance. It can tell us whether an object will sink or float in reference substance. Therefore,
$D = 1.54 \times 0.998 = 1.54g/ml$
Now, finding the mass for $1000ml$ we get
$1.54 \times 1000 = 1540g$
Now, we will find out the gram equivalent weight of acid,
$w = \dfrac{{molar \,mass}}{{Nfactor}} = \dfrac{{98}}{3} = 32.66g - eq$
As, the orthophosphoric acid is only $70\%$ pure,
The weight of acid,
$w = \dfrac{{1540 \times 70}}{{100}} = 1078g$
Number of gram equivalents of orthophosphoric acid,
$\Rightarrow \dfrac{{1078}}{{32.66}} = 33$
So, the 33 gram equivalents in $1000ml = 33N$
Calculating Normality we get,
$N = \dfrac{{No. \,of \, grameq.}}{{volume\,of\,Solution}} = 33N$

**Hence, the correct option C.

Additional Information: **
Orthophosphoric acid is an important chemical compound used in various industries and agriculture and also in products that we use in our daily lives. Some popular uses are removal of rust, in food and beverage, personal care, used in agriculture, pharma and many other uses. Some physical properties include that it is a white crystalline solid with melting point ${42.35^ \circ }C$ and density of $1.885g/ml$ .

Note:
Going step by step is important in calculations. You have to think about units necessarily.