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# How do you calculate the number of moles from molarity and volume?

Last updated date: 09th Aug 2024
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Hint:Since molarity is also given, we have to find the number of moles of a solution.
Molarity is generally defined as the amount of substance present in a certain volume of the solution.

So in the question it is given that how do we calculate the number of moles if we know the molarity and the volume of the given solution.
Before moving into the solution part of the question let's discuss briefly about various parameters like volume of the solution, molarity, number of moles etc.
So here first let’s discuss what volume of a solution means, in many problems we will be provided with the volume of the solution, but what does it actually refer to.
Volume of the solution is the mass of the solute divided by the concentration of the solution.
And the formulae is,$\text{Volume=}\dfrac{\text{mass}}{\text{concentration}}$
We use various parameters like molarity, molality, and normality to measure and represent the concentration of the solution.
Now let’s see what molarity refers to.
Molarity is the term used to express and measure the concentration of a solution if we know the amount of solute in the solution.
The molar concentration or molarity is expressed using the formulae,
$\text{Molarity(M)=}\dfrac{\text{moles}\,\text{of}\,\text{solute(n)}}{\text{Volume}\,\text{of}\,\text{solution}\,\text{in}\,\text{litre(V)}}$
Now let’s see what the number of moles means. Number of mole or simply moles are the measure of the solute substance present in the given sample solution. And one mole is equal to the value of Avogadro constant i.e. 1 mole has a value of $6.022\times {{10}^{23}}$ particles in them.
And now we got the idea that these three terms are interrelated.
And now the final part of the solution i.e. to find the number of moles of solute if molarity and volume given.$\text{m= }\!\!\rho\!\!\text{ }\!\!\times\!\!\text{ V}$
So from the equation of molarity, it’s clear that the formula consists of these both terms volume of solution and the number moles of the solute.
Hence let’s alter the equation of molarity in terms of number of moles of solute,$\text{Number of moles (n)=Molarity (M)}\times \text{Volume of solution in L(V)}$
$\text{n=M }\!\!\times\!\!\text{ V}$

Note:
We could find the number of moles if the weight of the solute (m) and the molecular mass (M) of the solute compound is known.
It can be calculated as,$n=\dfrac{m}{M}$
If we want to find the number of moles of a pure solid or liquid then we find the mass by multiplying the density of the substance with the volume term and the obtained mass (m) is then divided with molecular mass (M) to get the moles of solute.
-$\rho =\dfrac{m}{V}$, where $\rho$ is the density of solid or liquid
-$\text{m= }\!\!\rho\!\!\text{ }\!\!\times\!\!\text{ V}$$\text{n=}\dfrac{\text{m}}{\text{M}}$
-$\text{n=}\dfrac{\text{m}}{\text{M}}$