Question

1.0g of hydrogen contain 6.022×10^ 23 atoms the atomic weight of helium is 4 it follows that the number of atoms in 1g of He is ____

Answer 1

the no. of atoms in 1 mole of He is 6.022*10^23
4g of he =1 mole
1g of he =1/4 mole
=0.25 mole
therefore 0.25 mole = 6.022*10^23*0.25
= 1.5055*10^23

Answer 2

Given:

1.0g of hydrogen contain 6.022×10²³ atoms

The atomic weight of helium is 4u

To Find:

The number of atoms in 1g of He

Solution:

The number of atoms in 1g of He is 1.505×10²³.

We know that the molar mass of hydrogen is 1g.

Since the number of moles = Given Mass / Molar mass,

The number of moles in 1.0g of Hydrogen = 1/1 =1.

Hence there are 6.022×10²³ atoms in 1 mole of a substance.

Given that the atomic weight of helium is 4u

⇒ The molar mass of Helium = 4g

The number of moles of He in the provided sample = 1 / 4

Since there are  6.022×10²³ atoms in 1 mole (as proved above),

1/4 moles will have 6.022×10²³/ 4 atoms

= 1.505×10²³ atoms