A runner weighs 687 N and 71% of this weight is water. (a) H

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SUMMARY

The discussion centers on calculating the amount of water in a runner's body, who weighs 687 N. It is established that 71% of this weight is water, leading to a calculation of 49.77 g of H2O. The number of moles of water is determined using the formula n = m/molar mass, resulting in approximately 2.765 moles. The total number of water molecules is then calculated using Avogadro's number (6.022E23), yielding approximately 1.665 x 10^24 molecules.

PREREQUISITES
  • Understanding of weight and mass conversion (N to kg)
  • Familiarity with the concept of moles and molar mass
  • Knowledge of Avogadro's number (6.022E23)
  • Basic understanding of chemical formulas (H2O)
NEXT STEPS
  • Learn about unit conversions in physics, particularly between Newtons and kilograms.
  • Study the calculation of moles and how to apply the formula n = m/molar mass.
  • Research the significance of Avogadro's number in chemistry.
  • Explore the properties of water and its role in biological systems.
USEFUL FOR

Students in chemistry or physics, educators teaching these subjects, and anyone interested in the biochemical composition of the human body.

Alice7979
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Homework Statement


A runner weighs 687 N and 71% of this weight is water. (a) How many moles of water are in the runner's body? (b) How many water molecules (H2O) are there?

Homework Equations


n = N/NA
n= m/mass per mole
NA = 6.022E23
F=ma
H: 2*1
O: 16

The Attempt at a Solution


a)
687/9.8=70.1 g
70.1 * .71 = 49.77 g of h20
49.77/18 u = 2.765

b) 6.022E23 * 2.765 = 1.665
 
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Alice7979 said:
70.1 g
His mass is only 70.1 grams?! Check your units.
Alice7979 said:
6.022E23 * 2.765 = 1.665
What happened to the E23?
 
Alice7979 said:

The Attempt at a Solution


a)
687/9.8=70.1 g
70.1 * .71 = 49.77 g of h20
49.77/18 u = 2.765
Is this reasonable? A man who weighs 70.1 grams? Must be a world record...

(Posted at the same time as haruspex, oops)
 
Last edited:
I forgot the formula was in kg
 
Alice7979 said:
I forgot the formula was in kg
So does that change your answer?
 
haruspex said:
So does that change your answer?
Yes it did, thanks
 
Nathanael said:
(Posted at the same time as haruspex, oops)
Always happy to have corroboration.
 

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