Question

What is the mass of 4.30 mole of sodium?

Answer 1

Hint: Let us first understand what a mole is. One of the SI units of measurement that can be used to determine the amount of a substance is a mole. A mole of any substance has exactly $6.022\times {{10}^{23}}$ particles which can be ions, atoms, electrons, or molecules.

Complete answer:
We know that if one mole of a substance is present, it has exactly the Avogadro number $({{N}_{A}})$ of particles.
${{N}_{A}}=6.022\times {{10}^{23}}$
Now, the sum of the mass of all the particles in a sample gives the mass of a sample.
So, we can say that the mass of one mole of a compound is equivalent to the mass of all the particles contained in one mole of a substance i.e., $6.022\times {{10}^{23}}$ particles.
The molar mass of a substance is the mass of one mole of a substance. Even though it is usually expressed in g/mol, its SI base unit is kg/mol. Molar mass of a substance is not a molecular property, rather it is a bulk property of the substance.
Now, the molar mass of a substance is calculated by dividing the mass of the sample given and the number of moles of the sample given.
\[M=\dfrac{m}{n}\]
So, the mass of a sample containing a given number of moles can be given by
\[m\] =\[ n\times M \]
Where n = number of moles,
m = mass of given sample (in grams), and
M = molar mass of the sample (in g/mol).
Now, it is given to us that the number of moles n = 4.30.
And the molar mass of sodium (Na) is approximately M = 23 u
So, the mass of the sample containing 4.30 moles of sodium will be
\[m=4.3\times 23\]
m = 98.9 g.

Note:
It must be noted that in 2019, the SI base unit of molar mass was redefined. According to the new definition, the molar mass constant is
\[{{M}_{u}}=0.99999999965\times {{10}^{-3}}kg/mol\]
And not $1\times {{10}^{-3}}kg/mol$.
But for practical purposes, the molar mass of an element is still considered to be equivalent to the atomic mass of the element since the change is so insignificant.