Question

A runner weighs 560 N (about 130 lb), and 74% of this weight is water.

(a) How many moles of water are in the runner's body?
moles

(b) How many water molecules (H2O) are there?
molecules

I dont' unstand what to do here. I know have to fine mole per h2o

Answer 1

The runner weighs 560 N so his mass id 560/9.8 = 57.1 kg
so
.74 * 57.1 = 42.3 kg water

a mol of H2O = 2 grams + 16 grams = 18 grams = 18 * 10^-3 kg/mol

so moles of water = 42.3 kg / (18*10^-3 kg/mol) = 2.35 *10^3 moles

there are 6*10^23 molecules/mol of anything

so number of molecules = 2.35 * 10^3 *6*10^23
= 14.1*10^26 = 1.41 *10^27 molecules