One atomic mass unit has a mass of 1.6605 x 10-24 g. What is the mass of one molecule of H2O?

a. 2.991 x 10-23 g
b. 1.6605 x 10-24 g
c. 6.022 x 1023 g
d. 1.6605 x 10-24 u
e. 18.016 g

2.99×10⁻²³ g. Option a

Explanation:

Water → H₂O

We determine the molar mass of water → 1 g/mol . 2 + 16g/mol . 1 = 18g/mol

The molar mass means that 1 mol of water weighs 18 g.

We know that 1 mol contains 6.02×10²³ molecules. Therefore we would make a rule of three:

6.02×10²³ molecules of water weigh 18 g

1 molecule of water may weigh (1 . 18) / 6.02×10²³ = 2.99×10⁻²³ g