Gram/Mole Conversions

The atomic mass given in the periodic table gives the number of grams per mole for a given element. In other words, it reports the mass of Avigadro's number (6.02 x 1023) of atoms.

  1. Question: What is the mass of 3.01 x 1023 oxegen atoms?
    Method: Use the atomic mass of oxygen from the periodic table.
    (O: 16.0 g/mol)
    Solution:

        3.01 x 1023 O atom   1 mole             16.0 g
    ------------------ x ---------------- x ------ = 8.00 g
                         6.02 x 1023 atom   mole

  2. Question: How many flourine atoms are in a sample of 57.0 g of flourine?
    Method: Use the atomic mass of flourine from the periodic table.
    (F: 19.0 g/mol)
    Solution:

        57.0 g   mole     6.02 x 1023 atom
    ------ x ------ x ---------------- = 1.81 x 1024 atom
             19.0 g   mole

  3. Question: How grams of hydrogen are in a sample of 42.0 g of ammonia?
    Method: Use the molecular mass of ammonia (NH3) caluculated from the atomic masses of nitrogen and hydrogen from the periodic table
    (H: 1.01 g/mol; N: 14.0 g/mol)
    Solution:

        42.0 g   mole NH3   3 mole H   1.01 g
    ------ x -------- x -------- x ------ = 7.49 g
             17.0 g     mole NH3   mole H

  4. Question: How grams of oxygen are in a sample of 97.0 g of lead (II) nitrate?
    Method: Use the formula weight of lead (II) nitrate [Pb(NO3)2] caluculated from the atomic masses of lead, nitrogen and oxygen from the periodic table
    (Pb: 207.19 g/mol; N: 14.01 g/mol; O: 16.00 g/mol)
    Solution:

        97.0 g   mole Pb(NO3)2    6 mole 0        16.00 g
    ------ x ------------- x ------------- x ------- = 28.1 g
             331.21 g        mole Pb(NO3)2    mole O

Sample Problems

How many moles of oxygen atoms are in 4.00 grams of oxygen?
(O: 16.0 g/mol)
4.00 2.00 1.00 0.500 0.250
How many nitrogen atoms are in 7.00 grams of nitrogen?
(N: 14.0 g/mol)
1.20 x 1024 6.02 x 1023 3.01 x 1023 1.50 x 1023 7.50 x 1022
How many grams are contained in 1.81 x 1024 carbon atoms?
(C: 12.0 g/mol)
108. 36.0 12.0 4.00 1.33
How many grams of carbon are contained in 0.500 mol of methane (CH4)?
(C: 12.0 g/mol; H: 1.01 g/mol)
24.0 12.0 6.0 4.0 3.0
Patrick E. Fleming
Department of Chemistry and Biochemistry
California State University, East Bay
patrick.fleming@csueastbay.edu