Question

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 =

Answer 1

1. 10.0 g H = 9.92 moles

2. 0.25 g Na = 0.011 moles

3. 1.0 x 102 mg H2O = 0.0056 moles

Answer 2

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