Question

unit of narmality, molarity,molality​

Answer 1

TOPIC :- CONCENTRATION TERMS

NORMALITY (N)

Normality is defined as number of equivalent per unit volume.

$normality = \frac{number \: of \: equivalent}{volume \: in \: l}$

Where, number of equivalent = $\frac{given \: weight}{ \frac{gram \: equivalent}{n \: factor} }$

Hence, unit of normality is $eqv \: {l}^{- 1}$

Molarity (M)

Molarity is defined as number of mole of a solute present in one litre of the solution.

$\frac{no. \: of \: moles \: of \: solute}{vol. \: of \: soln. \: in \: l}$

Hence, unit of molarity is $mol \: {l}^{ - 1}$

Molality (m)

Molality is defined as number of moles of solute per unit weight of solvent in kg. ( Focus on 'solvent' and 'kg').

Molality = $\frac{no. \: of \: moles \: of \: solute}{weight \: of \: soln \: in \: kg}$

Hence, Molality has unit $mol \: {kg}^{ - 1}$

ADDITIONAL DETAILS FOR IIT-JEE

N-factor

• It stands for Normality factor.

• It is purely a number.Hence, has no units.

• It is reaction as well as compound dependent.

• For acids and bases, it is equal to their basicity or acidity. For example :- N-factor of H2SO4 is 2 because its basicity is 2.

N-factor of KMnO4.

There is a pneumonic for it . It is BAN -153.

• B - Basic , A - Acidic , N - Neutral

• It implies that n - factor of KMnO4 in basic medium i s 1, in acidic it is 5 and in neutral medium, it is 3.

N-factor of K2Cr2O7 ( Potassium dichromate)

• In JEE, its N-factor in acidic medium is asked which is 6.