AP Chemistry Unit 1 – Chapter 3: Isotopes, Empirical & Molecular formulas
Also complete problems #38 & 40 in Chapter 3 of Zumdahl
1. A hydrocarbon mixture consists of 60.0% by mass of C3H8 and 40% of CxHy. When 10.0 grams of this mixture
is burned, it yields 29.0 g CO2 and 18.8 g H2O as the only products. What is the formula of the unknown
hydrocarbon?
2. A thoroughly dried 1.271 g sample of Na2SO4 is exposed to the atmosphere and found to gain 0.387 g in mass.
What is the percent, by mass,
of2Na2SO .10H O in the resulting mixture of hydrate
4
2
4 and Na SO ?
3. A certain brand of lunch meat contains 0.10% sodium benzoate, NaC7H5O2, by mass as a preservative. If a person eats
2.52 ounces of this meat, how many mg Na will that person consume?
4. Three different brands of "liquid chlorine" for use in purifying water in home swimming pools all cost $1.00 per
gallon and are water solutions of NaOCl. Brand A contains 10% OCl by mass; brand B, 7% available chlorine (Cl) by
mass; and brand C, 14% NaOCl by mass. Which of the three brands would you buy?
5. A 0.1510 gram sample of a hydrocarbon produces 0.5008 gram CO2 and 0.1282 gram H2O in combustion
analysis. Its molecular weight is found to be 106. For this hydrocarbon, determine (a) it‟s percent composition; (b)
its empirical formula; (c) its molecular formula.