# Calculate the number of H2O molecules in a human body of mass 56.9 kg.?

Calculate the number of H2O molecules in a human body of mass 56.9 kg. Assume that, on average, water makes up 62% of the mass of a human body. (Use 1.0 u for the atomic mass of hydrogen, and 16.0 u for the atomic mass of oxygen

Relevance

56.9 * 0.62 = 35.278 kg of water in the body

35.278 kg of H20 = x moles

x = 35278/ Mr of water(18g) = 1959.889 moles of water

1 mole of water = Agravados constant of molecules per mole = 6.022 * 10^23 * mol^-1

Therefore 1959.889 moles of water = (1959.889 * 6.022 * 10^23) molecules in a human body of 56.9kg

Answer: approximately 1.180 * 10^27 molecules.

Hope it's right! :)

Source(s): I have some knowledge of chemistry.
• calculate number h2o molecules human body mass 785 kg assume average water

• 62% of 56.9 kg = 35.3 kg = 35 300 g

find the number of mol:

18.0 g = 1 mol of H2O

35 300 g = 1960 mol of H2O

find the number of molecules:

1 mol = 6,022 * 10^23 molecules (Avogadro's number)

1960 mol = 1.18 * 10^27 molecules