Question

How many moles of sodium nitrate, $NaN{{O}_{3}}$ would be produced from the complete reaction of 253g sodium chromate, $N{{a}_{2}}Cr{{O}_{4}}$?

Answer 1

Hint: Write the balanced chemical equation and then find out the ratio of the production of sodium nitrate, then use stoichiometry to calculate the number of moles produced.

Complete answer:
In order to answer the question, we need to know about moles and molar mass. Now, matter is made up of atoms, and as matter has mass, then the atoms should have an individual mass. Molar mass of an element or compound is the mass which houses $6\times {{10}^{23}}$ particles. For, example, the hydrogen molecule has a molar mass of 2 grams. This means 2 grams of hydrogen contains $6\times {{10}^{23}}$atoms, and this number is also called the Avogadro’s number.
Number of moles of an element or a compound is the ratio of its given mass taken by the user, to its molar mass. More is the number of moles, more is the concentration of the substance. Now, let us come to the question. First, we will write the complete balanced equation for the chemical reaction which is:
\[Pb{{(N{{O}_{3}})}_{2}}+N{{a}_{2}}Cr{{O}_{4}}\to PbCr{{O}_{4}}+2NaN{{O}_{3}}\]
We have been provided with 253 grams of $N{{a}_{2}}Cr{{O}_{4}}$ and with this, we have to find the number of moles of $NaN{{O}_{3}}$. The molar mass of $N{{a}_{2}}Cr{{O}_{4}}$ is $161.97g\,mo{{l}^{-1}}$ and according to the reaction, 1 mole of $N{{a}_{2}}Cr{{O}_{4}}$ reacts to give 2 moles of $NaN{{O}_{3}}$. So, by using this data, we can calculate the moles of $NaN{{O}_{3}}$ which is:
\[\begin{align}
  & mol{{e}_{NaN{{O}_{3}}}}=253gN{{a}_{2}}Cr{{O}_{4}}\times \left( \dfrac{1mol\,N{{a}_{2}}Cr{{O}_{4}}}{161.97g\,N{{a}_{2}}Cr{{O}_{4}}} \right)\times \left( \dfrac{2\,mol\,NaN{{O}_{3}}}{1\,mol\,N{{a}_{2}}Cr{{O}_{4}}} \right) \\
 & \Rightarrow mol{{e}_{NaN{{O}_{3}}}}=3.12mol \\
\end{align}\]
So, approximately 3 moles of $NaN{{O}_{3}}$ can be obtained, by reacting 253 grams of $N{{a}_{2}}Cr{{O}_{4}}$.

Note: The following method is used in order to calculate the mass to mole calculations:
\[Quantity\,sought=Quantity\,given\times Conversion\,factor\]
Also, the number of moles is a dimensionless quantity.