Question

Total no. of atoms in 90 g of water

Answer 1

The molecular mass of water(H2
O)= 2×1+16

=18gmol−1


So, According to the mole concept;
18g of water has 6.022×1023

molecules in it.
1g of water has 6.022×1023


18

molecules in it.


Then, 90 g of water has6.022×1023


18
×90
molecules in it.


90g of water has6.022×1023
×5
molecules in it.
Now, 1 water molecule has 3 atoms in it.
So the number of atoms present in 90g of water is;
​=6.022×1023
×5×3
=90.33×1023

=9.03×1024

​


Hence, 90 g of water have 9.03×1024

atoms in it.


Tip

1 mole of an element or molecule contained 6.022
×10
23
atoms or molecules present in it.
The water molecule has 2 hydrogen atoms and 1 oxygen atom in it.

Answer 2

Step 1: Determine the molecular weight of water. The molecular weight of water is 18.015 g/mol.

Step 2: Calculate the number of moles. To calculate the number of moles, divide 90g by the molecular weight of water to get 5 moles of water.

Step 3: Calculate the number of atoms of water present. One mole of water contains 6.022 x 10^23 molecules of water. Therefore, 5 moles of water contains (5 x 6.022 x 10^23) = 3.011 x 10^24 atoms of water.

Therefore, there are 3.011 x 10^24 atoms of water present in 90g of water.