Exercises 87What is the ratio of percent by mass of copper in the an-
hydrous compound to the percent by mass of copper in
the hydrated compound?CONCEPTUAL EXERCISES
100.What mass of NaCl would contain the same totalnumber
of ions as 245 g of MgCl 2?
101.How many atoms of oxygen are in 17.9325 g of sulfuric
acid?
102.In the “button” and “button hole” analogy of writing for-
mulas for ionic compounds, one may think of positive
charges as buttons and negative charges as button holes.
One prepares formulas by combining the buttons (positive
charges) with an equal number of button holes (negative
charges) so that every button will be associated with a sin-
gle buttonhole and vice versa. Using this analogy, how
many buttons (positive charges) are associated with a single
cation (positive ion) in each of the following ionic com-
pounds? (a) NaCl; (b) Na 2 SO 4 ; (c) CaSO 4 ; (d) Al 2 (SO 4 ) 3.
103.Two deposits of minerals containing silver are found. One
of the deposits contains silver oxide, and the other con-
tains silver sulfide. The deposits can be mined at the same
price per ton of the original silver-containing compound,
but only one deposit can be mined by your company.
Which of the deposits would you recommend and why?
104.A decision is to be made as to the least expensive source
of zinc. One source of zinc is zinc sulfate, ZnSO 4 , and an-
other is zinc acetate dihydrate, Zn(CH 3 COO) 2 2H 2 O.
These two sources of zinc can be purchased at the same
price per kilogram of compound. Which is the most eco-
nomical source of zinc and by how much?105.Assume that a penny is 116 in. thick and that the moon is
222,000 mi at its closest approach to the earth (perigee).
Show by calculation whether or not a picomole of pennies
stacked on their faces would reach from the earth to the
moon.BUILDING YOUR KNOWLEDGENOTE Beginning with this chapter, exercises under the “Building
Your Knowledge” heading will often require that you use skills, concepts,
or information that you should have mastered in earlier chapters. This
provides you an excellent opportunity to “tie things together” as you study.106.A 22-mL (19-g) sample of an unknown liquid is analyzed,
and the percent composition is found to be 53% C, 11%
H, and 36% O. Is this compound likely to be ethanol,
CH 3 CH 2 OH? Give two reasons for your answer. (Hint:
See Table 1-8.)
107.Three allotropes of phosphorus are known, with molecu-
lar weights of 62.0, 31.0, and 124.0 amu, respectively.
Write the molecular formula for each allotrope.
108.Near room temperature, the density of water is 1.00 g/mL,
and the density of ethanol (grain alcohol) is 0.789 g/mL.
What volume of ethanol contains the same number of mol-
ecules as are present in 175 mL of H 2 O?
109.Calculate the volume of 2.00 mol of mercury, a liquid
metal. (Hint:See Table 1-8.)
110.In Chapter 1 you learned that the specific heat of water is
4.18 J/g°C. The molar heat capacity is defined as the
specific heat or heat capacity per mole of material.
Calculate the molar heat capacity for water. What value(s)
limited the number of significant figures in your answer?