Question

How many atoms are contained in 23g of sodium? ($Na = 23u$)

Answer 1

Hint: Sodium is an alkali metal with atomic number 11. The electronic configuration of sodium atom is $1{s^2}2{s^2}2{p^6}3{s^1}$.
Here we have to calculate the number of atoms in 23g of sodium. To calculate the number of atoms in 23g of sodium, we first need to calculate the number of moles of sodium atom in 23 g of sodium.

Formula Used: The formula we will be using for calculating the number of moles of sodium atom in 23g of sodium is as follows:
$n = \dfrac{m}{M}$
Here, n represents the number of moles of sodium atom.
The mass of sodium is denoted as m and M is the molar mass of sodium atom.

Complete step by step answer:
To solve this problem, we will first calculate the number of moles of sodium atom by using the following formula.
 $n = \dfrac{m}{M}$……………………… (1)
Let us first write down the given quantities in the question.
$m = 23g$
$M = 23g/mol$
Remember that molar mass of sodium is its average atomic mass which is approximately 23.
Step 1: Let us calculate the number of moles of sodium atom in 23g of sodium.
On putting the respective values in formula (1), we get
$\therefore n = \dfrac{{23}}{{23}}$
$\therefore n = 1mole$
The number of moles of sodium atom in 23g of sodium is 1 mole.
Step 2: We know that, $6.023 \times {10^{23}}$ atoms are present in one mole of any substance. Here, the value $6.023 \times {10^{23}}$ is known as Avogadro’s number.
For 23g of sodium, $n = 1mole$
Therefore, 23g of sodium contains $6.023 \times {10^{23}}$ atoms of sodium.

Additional information:
The Avogadro’s number or Avogadro’s constant is the number of units present in a mole of any substance. The units here referred to the atoms, electrons, ions or molecules depending upon the nature of the substance.
The credit for the concept of Avogadro’s number is given to the scientist Amadeo Avogadro, even though he did not calculate the exact value of Avogadro’s number.

Note: Students should keep in mind that the molar mass of an atom is equal to its average atomic mass. But, in case of a compound, the molar mass is equal to the sum of the average atomic masses of the constituent elements.
For example, the molar mass of ${H_2}O$ can be calculated as follows:
${M_{{H_2}O}} = (2 \times 1) + (1 \times 16) = 18g/mol$