Question

The number of moles of ${\text{NaCl}}$ in $3{\text{L}}$ of $3{\text{M}}$ solution is:
A. $1$
B. $3$
C. $9$
D. $27$

Answer 1

Hint: Stoichiometry is the study of the quantitative aspects of chemical reactions. Chemical equations are concise representations of chemical reactions. Mole is defined as the quantity of a substance that contains the same number of ultimate particles as are present in $12{\text{g}}$ of carbon$ - 12$. Molarity is the number of moles of solutes per litre of solution.

Complete step by step answer:
Stoichiometry deals with the numerical relationships of elements and compounds and the mathematical proportions of reactants and products in chemical transformations. Concentration is the amount of solute dissolved in a given amount of solution. There are different types of concentration units. Formula and molecular mass deal with individual atoms and molecules. Mole is the unit that relates the number of particles and mass.
Molarity is a concentration unit that describes how much of a substance is dissolved in a solution.
i.e. Molarity, ${\text{M}} = \dfrac{{\text{n}}}{{\text{V}}}$, where ${\text{n}}$ is the number of moles of solute and ${\text{V}}$ is the volume of solution in litres.
Now we have to calculate the number of moles from this formula.
It is given that the molarity, ${\text{M = 3M}}$
Volume of solution, ${\text{V = 3L}}$
Substituting these values in the equation, we get
${\text{3M}} = \dfrac{{\text{n}}}{{{\text{3L}}}} \Leftrightarrow n = 3 \times 3 = 9{\text{mol}}$
i.e. the number of moles of ${\text{NaCl}}$ in $3{\text{L}}$ of $3{\text{M}}$ solution is $9{\text{mol}}$

Hence the correct option is C.

Note:
Moles provide a bridge from molecular scale to real-world scale. One mole of molecules or formula units contain Avogadro number times the number of atoms or ions of each element in the compound. Each chemical equation provides information about the amount of reactants produced. Mole concepts enable us to solve stoichiometric problems involving mass relations of reactants and products in chemical reactions.