Question

How do you calculate the number of moles from volume?

Answer 1

Hint Molarity can be defined as the moles of solute in one litre of solution. Density of substance can be said as mass per volume.

Complete answer:
So in the question it is asked how can we calculate the number of moles if volume of the solution is given.
Now let’s see what a solution is.
Solution can be said as the homogenous mixture of two or more substances.
A solution consists of two parts i.e. a solute and a solvent. Solute is that particle which gets dissolved uniformly in a medium and the solvent is the substance in which the solute particles dissolve.
We generally give the term solutions for mixtures which possess the liquid state but solutions of gas and solid are also known.
From the time we study about solutions, we represent the concentration of the solutions by the terms molarity, molality, normality etc.
So we use these terms to represent the concentration of the solution i.e. how much solute is dissolved in the given volume of solvent.
The other term given in the question is number of moles or can be said as moles of solute it is the amount of solute present in solute in terms of mole.
A mole of a substance is that value equal to Avogadro number particles. The Avogadro constant has a value of $6.022\times {{10}^{23}}$particles.$6.022\times {{10}^{23}}$
Now we can discuss how to calculate the number of solutes from the volume.
- If we take the case of pure liquids or solids then we take the density of the solid and liquids to calculate the number of moles of solute. We know that the density ($\rho $) can be defined as the mass per volume of the solution.
$Density\left( \rho \right)=\dfrac{Mass(m)}{Volume(V)}$
By altering the equation we will get mass of the solute,
$Mass(m)=Density\left( \rho \right)\times Volume(V)$
From the equation we will get the mass and divide the obtained mass with the molecular mass of the substance we will get the number of moles of solute.
$No.\,of\,moles\,of\,solute(n)=\dfrac{mass(m)}{Molecular\,mass(M)}$
-If we take the solutions whose molarity is given then we could find the number of moles of solutes directly, since we know that the molarity (M) is equal to the number of moles of solute present in one litre of the solution.
$M=\dfrac{n}{V}$
$n=M\times V$

Note: The unit of number of moles of solute is mol. And we can find the number of moles if we know the mass of the substance and mass of one mole.
$\text{Number}\,\text{of}\,\text{moles}\,\text{of}\,\text{solute=}\dfrac{\text{Mass}\,\text{of}\,\text{substance}}{\text{Mass}\,\text{of}\,\text{one}\,\text{mole}}$