1. Naturally occurring boron exists in two isotopic forms: the more common isotope is ¹¹B which is 80.00% abundant. Given that the average atomic mass of boron is 10.81, what is the atomic mass of the second isotope?

2. A metal M forms an oxide having the formula M₂O₃, containing 68.4% metal by mass. Calculate the atomic mass of the metal.

3.Cortisone consists of molecules each of which contains 21 atoms of carbon (plus other atoms). The mass percentage of carbon in cortisone is 69.98%. What is the molecular mass of cortisone?

4. NaHCO₃ is the active ingredient in baking soda. How many grams of oxygen are in 0.35 g of NaHCO₃?

5.Phenol is a compound which contains 76.57% carbon, 6.43% hydrogen, and 17.0% oxygen. Calculate the empirical formula of phenol.

6. A 2.00-g sample of a compound composed of C and H is burned, forming 6.62 g of CO₂ and 1.69 g of H₂ O. What is the empirical formula of the compound?

7. How many grams of Ca(NO₃)₂ can be produced by reacting excess HNO₃with 7.40 g of Ca(OH)₂?

8. Sulfuric acid may be produced by the following process:

4FeS₂ + 11O₂ ---> 2Fe₂O₃ + 8SO₂

2SO₂ + O₂ ---> 2SO₃

SO₃ + H₂O ---> H₂SO₄

How many moles of H₂SO₄will be produced from 5.00 moles of FeS₂?

9. The following two reactions are important in the blast furnace production of iron metal from iron ore (Fe₂ O₃).

2C(s) + O₂ (g) ---> 2CO(g)

Fe₂ O₃ + 3CO(g)---> 2Fe + 3CO₂ (g)

Using these balanced reactions, how many moles of Oé are required for the production of 5.00 kg of Fe (molar mass = 55.85)?

10. A 0.4647-g sample of a compound known to contain only carbon, hydrogen, and oxygen was burned in oxygen to yield 0.8635 g of CO₂ and 0.1767 g of H₂O. What is the empirical formula of the compound?

Answers: #1= 10.05 amu, #2 = 51.8 g/mol, #3 = 359.9g/mol, #4 = 0.20 g, #5= C₆H₆O, #6 = C₄H₅ #7 = 164 g

#8 = 10 mol, #9= 67.2 mol, #10= C₃H₃O₂

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