Question

Calculate the no. of atoms present in 81g of Aluminium.
(Hint: Al - atm , mass - 27)​

Answer 1

Answer- The above question is from the chapter 'Some Basic Concepts of Chemistry'.

Concept Used: 1) Number of moles = $\dfrac{Given \: mass}{Molar \: mass}$

2) No. of atoms = Number of moles × Avogadro's Number

Avogadro's Number = 6.022 × 10²³

Given question: Calculate the no. of atoms present in 81 g of Aluminium.

(Atomic mass of Al = 27 u.)

Answer: Given mass of Al = 81 g

Molar Mass of Al = 27 g

Number of moles of Al = $\dfrac{Given \: mass}{Molar \: mass}$

Number of moles of Al = $\dfrac{81}{27}$

Number of moles of Al = 3

Number of atoms of Al = Number of moles of Al × Avogadro's Number

Number of Al atoms = 3 × 6.022 × 10²³

Number of Al atoms = 18.066 × 10²³

Number of Al atoms = 1.8066 × 10²⁴ atoms

∴ Number of Al atoms = 1.8066 × 10²⁴ atoms