Question

Which of the following terms are unitless?
(i) Molality
(ii) Molarity
(iii) Mole fraction
(iv) Mass percent

Answer 1

both (iii) Mole fraction and (iv) Mass percent are unitless

Answer 2

Answer: (iii) Mole fraction

(iv) Mass percent

Explanation:

1. Molarity of a solution is defined as the number of moles of solute dissolved per Liter of the solution.

$Molarity=\frac{n}{V_s}$

where,

n= moles of solute

$V_s$ = volume of solution in L

$Molarity=moles/L$

2. Molality of a solution is defined as the number of moles of solute dissolved per kg of the solvent.

$Molarity=\frac{n}{W_s}$

where,

n = moles of solute  

$W_s$ = weight of solvent in kg

$Molality=moles/kg$

3. Mole fraction is the ratio of moles of one component to the total number of moles.

$x_{A}=\frac{\text {moles of A}}{\text {moles of A+moles of B}}$

Thus has no units.

4. Mass percent is the ratio of mass of one component to the total mass.

To calculate the mass percent of element in a given compound, we use the formula:

$\text{Mass percent}=\frac{\text{Mass}}{\text{Total mass}}\times 100$

Thus has no units.