Prince George’s Community College
CHM1010 (Mr. Shah)
Chapter 3: The mole, empirical formulas
1. How many atoms of copper are there in a piece of pure copper wire that weighs 143g?
(1.35 x 1023 atoms)
2. What are the mass in grams of one molecule of carbon tetrachloride? (2.56 x 10-22g)
3. Chlorophyll a green pigment in leaves has the formula C55H72MgN4O5. If 0.0011g of magnesium is
available to a plant cell for chlorophyll a synthesis, how many grams of carbon will be required
to completely use up the magnesium? (0.030g C)
4. A 2.57g of sample of a compound composed of only tin and chlorine was found to contain 1.17g
of tin. What is the compounds empirical formula? (SnCl4)
5. A 1.525g sample of a compound between nitrogen and oxygen contains 0.712g of nitrogen.
Calculate its empirical formula.
6. One of the compounds of iron and oxygen, “black iron oxide” occurs naturally in the mineral
magnetite. When a 2.448g sample was analyzed it was found to have 1.771g of Fe. Calculate the
empirical formula of this compound. (Fe3O4)
7. A white powder used in paints, enamels, and ceramics has the following percentage
composition: Ba 69.6%, C 6.09%, O 24.3%, what is its empirical formula? (BaCO3)
8. A 0.5438g sample of a liquid consisting of only C, H and O was burned in pure oxygen, and
1.039g of CO2 and 0.6369g of water were obtained. What is the empirical formula of the
compound? (C2H6O)
9. The composition of a 5.048g sample of a compound of C, H, and O gave 7.406g CO2, and 3.027g
of H2O. Calculate the empirical formula of the compound?
10. The empirical formula of hydrazine is NH2, and its molecular mass is 32.0g/mol. What is the
molecular formula?
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