Question

What is the mass of \[NaCl\] required to prepare $0.5$ liters of a $2.5$ molar solution of \[NaCl\] ?

Answer 1

Hint:To solve this type of question firstly we need to calculate the number of moles \[NaCl\] of at present. The mole is a unit of measurement for an amount of the subsequent in system unit that too not standard but International System. A mole of the substance is the mole of particles which are defined as containing exactly.

Complete solution:
The molecular weight of \[NaCl\] can be defined as \[58.44\text{ }\dfrac{g}{mol}\] Here its cleared that one mole of \[NaCl\] weights around \[58.44\text{ }g\]
Also as per the given values, a \[2.5\text{ }M\] solution is taken here \[2.5\] moles per liter is just Molarity and its just the number of moles per liter.
Therefore, we know that \[0.5\text{ }L\] would contain \[1.25\] mol right now we need to calculate for molecular weight \[1.25\text{ }\times \text{ }58.44\text{ }g\text{ }=\text{ }73\text{ }g\]
The following sets can be written as
\[M\text{ }=\text{ }moles/vol\text{ }\ldots \ldots \ldots \ldots \left( i \right)\]
Here \[M\] is for molarity.
\[vol\text{ }=\text{ }volume\text{ }\left( in\text{ }liters \right)\]
\[moles\text{ }=\text{ }\dfrac{grams}{MW}\text{ }\ldots \ldots \ldots \ldots \left( ii \right)\]
Here $g$ is the weight of a compound and $MW$ is molecular weight.
Substituting the value of moles in equation \[\left( i \right)\] we get;
\[M\text{ }=\text{ }\dfrac{\left( \dfrac{g}{MW} \right)}{vol}\text{ }\ldots \ldots \ldots \ldots \left( iii \right)\]
Here we need to find the value of $g$
Therefore, rearranging the equation \[\left( iii \right)\] we get;
\[g\text{ }=\text{ }M\times ~MW\times ~vol\text{ }\ldots \ldots \ldots \ldots \left( iv \right)\]
Substituting the acquired values in equation \[\left( iv \right)\]
\[g=2.5\dfrac{mol}{L}\times 0.5\text{ }L\times 58.44\dfrac{g}{mol}\]
\[g\text{ }=\text{ }73g\]
Therefore $73g$ mass of \[NaCl\] required to prepare $0.5$ liters of a $2.5$ molar solution of \[NaCl\].

Note:Note that while calculating mass of compound we need acquire molecular weight of Compound without molar mass we can't get further also the important formula for determining mass \[M\text{ }=\text{ }\dfrac{moles}{vol}\] and likewise \[moles\text{ }=\text{ }\dfrac{grams}{MW}\] and after substituting we acquire the mass of \[NaCl\] or required compound.