Percent Composition
63. In a class of 76 students, the results of a particular examination were 7 A’s, 22 B’s, 37 C’s, 8
D’s, 2 F’s. What was the percent distribution of grades, that is, % A’s, % B’s, and so on?
9.2% A, 28.9% B, 48.7% C, 11% D, 3% F
64. A class of 84 students had a final grade distribution of 18% A’s, 25% B’s, 32% C’s, 13%
D’s, 12% F’s. How many students received each grade?
65. A solution of sucrose in water is 28.0% sucrose by mass and has a density of
What mass of sucrose, in grams, is contained in 3.50 L of this solution?
66. A solution containing 12.0% sodium hydroxide by mass in water has a density of
What -volume of this solution, in liters, must be used in an application requiring 2.75 kg of
sodium hydroxide?
Integrative and Advanced Exercises
67. According to the rules on significant figures, the product of the measured quantities 99.9 m and
1.008 m should be expressed to three significant figures—
Yet, in this case, it would
be more appropriate to express the result to four significant figures—
Explain why.
68. For a solution containing 6.38% para-dichlorobenzene by mass in benzene, the density of the
solution as a function of temperature (t) in the temperature range 15 to 65 °C is given by the
equation
69. A solution used to chlorinate a home swimming pool contains 7% chlorine by mass. An ideal
chlorine level for the pool is one part per million (1 ppm). (Think of 1 ppm as being 1 g
chlorine per million grams of water.) If you assume densities of
for the chlorine
solution and
for the swimming pool water, what volume of the chlorine solution,
in liters, is required to produce a chlorine level of 1 ppm in an 18,000-gallon swimming
pool?
70. A standard 1.000 kg mass is to be cut from a bar of steel having an equilateral triangular