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

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

To find the number of moles of water in the runner's body, we need to use the given percentage and convert it to moles. Here's how you can do it:

Step 1: Convert the weight of the runner from Newtons to kilograms. Recall that the weight is given in Newtons, and the conversion factor from Newtons to kilograms is 1 kg = 9.81 N.

Weight in kg = Weight in N / 9.81

Step 2: Calculate the weight of water in the runner's body using the given percentage.

Weight of water = 74% * Weight of the runner

Step 3: Convert the weight of water to grams. Recall that 1 kg = 1000 grams.

Weight of water in grams = Weight of water in kg * 1000

Step 4: Calculate the number of moles of water using the molar mass of water. The molar mass of water (H2O) is approximately 18.015 g/mol.

Number of moles of water = Weight of water in grams / Molar mass of water

To find the number of water molecules (H2O), you can use Avogadro's number, which states that 1 mole of any substance contains 6.022 x 10^23 particles (atoms, molecules, or ions).

Number of water molecules = Number of moles of water * Avogadro's number (6.022 x 10^23)

Following these steps should help you calculate the answers to questions (a) and (b).