Question

Choose the correct statement:
Normality and molarity of HCl are same
Molality and molarity are independent of temperature.
Normality of 1M $KMn{O_4}$ in acidic medium is 5N.
A.All are correct
B.Only (ii) wrong
C.Only (iii) correct
D.All are wrong

Answer 1

We know that molality is mass of solute in kilogram of the solvent. Molarity is the moles of solute in one liter of the solution and normality is the number of gram equivalents to the volume of the solution.

Complete step by step answer:
We can write the formula of normality as,
${\text{Normality}} = \dfrac{{{\text{Number of gram equivalents}}}}{{{\text{Volume}}}}$
We can define Molarity as the mass of solute in one liter of solution. Molarity is the desired concentration unit for stoichiometry calculations. The formula is,
${\text{Molarity}} = \dfrac{{{\text{Moles of solute}}\left( {{\text{in moles}}} \right)}}{{{\text{Volume of solution}}\left( {{\text{in litres}}} \right)}}$
(i) Normality and molarity of HCl are same
The given statement is true because HCl is a monobasic acid. Its equivalent mass and the molecular mass are the same.
We can also say that normality is the product of molarity and n-factor. In the case of hydrochloric acid, the n-factor is one.
So, $normality = molarity \times n - factor$
$normality = molarity \times 1$
$normality = molarity$
So, for hydrochloric acid the normality and molarity is the same (equal).
Therefore, statement (i) is correct.
(ii) Molality and molarity are independent of temperature.
We have to know the major advantage of using molality as a unit of concentration is that molality depends on the weights of solute and weights of solvent that are unaffected with respect to changes in temperature and pressure.
Whereas, solutions that are prepared volumetrically such as molar concentration or mass concentration are subjected to change with respect to temperature and pressure change.
Therefore, the statement (ii) is incorrect.
(iii) Normality of 1M $KMn{O_4}$ in acidic medium is 5N.
In an acidic medium, $KMn{O_4}$ dissociates into $M{n^{2 + }}$. The equation is written as,
$KMn{O_4} \to M{n^{2 + }}$
In this case, the value of n-factor is five.
We can also say that normality is the product of molarity and n-factor. In case of potassium permanganate, the n-factor is five and the molarity is 1M.
So, $normality = molarity \times n - factor$
$normality = 1 \times 5$
$normality = 5N$
The normality of potassium permanganate in acidic medium is $5N$.
Therefore, the statement (iii) is correct.
Among the given statements only statement (ii) is wrong.
Therefore, option (B) is correct.

Note:
We must remember that in various applications, the molality carries major advantages because the mass, or the amount, of a substance is frequently more essential than its volume. Another major advantage of molality is that the molality of one solute present in a solution is independent of the absence (or) presence of other solutes.