In each of the following, how many moles of each element or compound are present? 10.0 g H = 0.25 g Na = 1.0 x 102 mg H2O =

Moles = mass / molar mass

moles of H = 10g/1g/mol (molar mass of H) = 10 moles of H

moles of Na = 0.25g / 23 g/mol (molar mass of Na) = 0.0109 moles of Na

moles of H20 = mass of water / molar mass of water (18 g/mol)

mass of water in g = 1 g = 1000mg what about 1 x10^2 mg = ? g

100mg x1g/1000mg=0.1 g

moles is therefore = 0.1g / 18 g/mol = 5.556 x10^-3moles of H20