Question

How do you determine the number of moles of argon in $452g$ of Argon?

Answer 1

Hint : We know that Argon is an element denoted as $Ar.$ It has an atomic number $18.$ It is also a noble gas as the atoms of this element have their orbitals full (complete octet). Its valency is $0.$ It lies in the group $18$ of the periodic table. It is also the third-most abundant gas in the Earth’s atmosphere.

Complete Step By Step Answer:
The mass of an atom of a particular chemical substance is called its atomic mass. Generally to get a rough idea about atomic mass we add the number of protons and neutrons present in the nuclei of the atom and write u next to it as its unit although this approximation is not true for every atom. One mole of a substance comprises Avogadro's number of particles of the substance in it. Molar mass of a substance is the mass of one mole particle of the substance in grams. Knowing this we can now go on to calculate the number of moles of Argon.
We know that the atomic number of Argon is $18$ . And the atomic mass of argon is $39.94g$ . We will use the mole concept to determine the moles of argon. We have the total mass of argon as $452g$ . One mole of argon contains $39.94g$ of argon which is also called the molar mass of Argon. Thus, n moles of argon contain $452g$ mass of argon
Thus, to determine the number of moles we will divide the total mass of argon by its molar mass.
$n=\dfrac{total\text{ }mass\text{ }of\text{ }Argon}{one\text{ }mole\text{ }of\text{ }Argon}=\dfrac{452g}{39.94}=11.31moles$
$\Rightarrow n=11.31moles.$
Therefore, total $11.31moles$ are present in $452$ g of argon.

Additional Information:
In questions like above what becomes most essential is the approximate knowledge of molar mass of various atoms, as clearly mentioned in the hint we can get an approximate idea of molar mass from the number of nucleons present in the nucleus of an atom specially for atoms with atomic number less than or equal to $20$ . Also be careful about the units of molar mass which is grams per mole.

Note :
We must remember that the argon is also called as inert gas due to its unreactive nature. Unlike metals and non-metals. Metals have oxidation states ranging from $+1\text{ }to\text{ }+3$ thus they can react with other metals to complete their octet. Same is for non-metals as well; the only difference is non-metals have oxidation states ranging from $-1\text{ }to\text{ }-3.$ Mostly, the argon present in the earth’s atmosphere is radiogenic argon $-40$ which is derived from the decay of $potassium-40$ . Argon is soluble in water. Physically it is colorless, odorless, nonflammable and non-toxic gas. It can exist in three states- as solid, liquid or gas.