Question

Mole of electrons present in 9 g of aluminium is
(Atomic mass of Al = 27 u)
4 0.33
(2) 4.33
(3) 1.33
(4) 2.66
​

Answer 1

0.33 (ie) 9/27 given mass/molar mass

Answer 2

Answer:

Option (2)

9 grams of Aluminium contains 4.333 mole electrons.

Explanation:

Provided that:

Atomic mass of Aluminium (Aluminium-27) = 27 u or 27 amu

Given mass of Aluminium (w) = 9 gm

The molar mass of Aluminium is (m) = 27 gm

So 1 mol of Al will weigh 27 grams

Then 9 grams of Al is equivalent with:

$n = number \: of \: moles \\ \\ n \: = \frac{w}{m} \\ so \: n \: = \frac{9}{27} \\ = \frac{1}{3} \: mole$

Hence 9 grams of Al is equivalent with 1/3 mole Al.

We know that 1 mole of any substance contains Avogrado number of atoms.

$Avogardo \: Number (NA) = 6.022 \times {10}^{23}$

And we know that the Atomic number of Aluminium is 13 . That means one atom of Aluminium has 13 protons and 13 electrons .

Hence number of electrons in 1 mole Aluminium is 13 × Avogardo Number (NA) .

And 1 mole electron = Avogardo Number (NA) electron

So we get 1 mole of Aluminium contains 13 mole of electrons .

Hence in 1/3 mole of Aluminium we get:

$1 \: mole \: Al = 13 \: mole \: electrons \\ \\ so \: \frac{1}{3} \: mole \: Al = \frac{13}{3} 13 \: mole \: electrons \\ or \: \frac{1}{3} \: mole \: Al = 4.333 \: mole \: electrons$

So 1/3 mole of Aluminium contains 4.333 mole electrons.

Hence 9 grams of Aluminium contains 4.333 mole electrons.