Question

How are stoichiometry and molarity related?

Answer 1

Stoichiometry is the relation used to relate masses of reactants and products of a reaction using a balanced chemical reaction. Molarity on the other hand is the measure of moles of a substance present in $1000ml$ or$1l$ of a solution, it helps us in getting information about the concentration of a substance present in the reaction mixture.

Complete step-by-step answer:
Stoichiometry is founded upon the principle of Law of Conservation of Mass which states that the total mass of reactants is equal to the total mass of products during a chemical reaction. Using stoichiometry, we empirically relate the various reactants and products with each other thus making it easier to keep track of the mass of reactant to be supplied for getting a certain amount of product and vice versa. To illustrate how stoichiometry and molarity ultimately relate to each other let us take an example,

Say, ${V_1}ml$of $xM$compound$A$is mixed with ${V_2}ml$of$yM$compound$B$ to give products shown by the following balanced chemical equation:
$2A + 3B \to 3C$

From the Balanced chemical equation we can say that $2$ moles of$A$ reacts with $3$ moles of$B$to give $3$ moles of$C$, by using the above stoichiometric relation and the number of moles of reactant provided we can obtain the yield of product obtained and reactant left unused. To know the number of moles we ultimately need Molarity as:
Number of moles $\left( n \right) =$ Molarity$\left( M \right)$ $\times$Volume of substance$\left( V \right)$ provided in liters $\left( l \right)$
So, Stoichiometry is ultimately linked to Molarity via the number of moles of a substance.

Note: While connecting molarity with moles via volume we should always be careful about the units i.e., if Molarity is in $g\,m{l^{ - 1}}$ then the volume multiplied should also be in $ml$otherwise a grave error in calculation could sink in. Also, for determining stoichiometric relations always use balanced reactions.