Question

What is the mole fraction of solvent in 2.5 m aqueous solution?
A. 0.043
B. 0.957
C. 0.085
D. 0.25

Answer 1

Hint: Mole fraction is the general way to express the concentration of a solution. It is generally represented by the number of molecules of a particular component in a mixture divided by the total number of moles in the given mixture.

Complete Solution :
- Mole is generally represented by mol which is used to measure the amount of any substance. A mole of any substance or a mole of particles is defined to be exactly equal to \[6.02214076\times {{10}^{23}}\] particles and particles may be ions, atoms, electrons or molecules.

Mole fraction is generally represented by X and given by the formula:
- $Mole~fraction~of~solute = \dfrac{Moles~of~solute}{moles~of~solute + moles~of~solvent}$
Solute is the substance which is mixed in any component or we can say that solute is anything which is being mixed and solvent is the substance in which solute gets mixed.
Here 2.5 m represents 2.5 molal solution i.e. 2.5 moles of solute in 1 kg solvent and this represents
Moles of solute = 2.5
Moles of water or solvent = $\dfrac{1000}{18} = 55.55$ (As given compound is aqueous solution so solvent is water here)
- Now we have to calculate mole fraction of solute which can be calculated by the formula as mentioned above
$Mole~fraction~of~solute = \dfrac{2.5}{2.5 + 55.55}$
$Mole~fraction~of~solute = \dfrac{2.5}{58.05}=0.043$
So, the correct answer is “Option A”.

Note: Solute is the substance which is present in less amount and solvent is that substance which is present in higher amount as compared to solute. Solute and solvent combined to make a solution. Mole fraction represents the fraction of molecules.