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110 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 11
6. How many grams of chlorine gas must be reacted with excess
sodium iodide (NaI) to produce 6.00 moles of sodium chloride?
a. Balance the equation: NaI(aq) ϩ Cl 2 (g) 0
NaCl(aq) ϩ I 2 (s).
b. Perform the calculation.
7. Calculate the mass of hydrochloric acid (HCl) needed to react
with 5.00 moles of zinc.
a. Balance the equation: Zn(s) ϩ HCl(aq) 0
ZnCl 2 (aq) ϩ H 2 (g).
b. Perform the calculation.
Stoichiometric mass-to-mass conversion If you were preparing to carry out a chemical reaction in the laboratory, you would
need to know how much of each reactant to use in order to produce
a certain mass of product. This is one instance when you would use
a mass-to-mass conversion. In this calculation, you can find the
mass of an unknown substance in a chemical equation if you have
the balanced chemical equation and know the mass of one substance
in the equation.
Example Problem 11-4
Stoichiometric Mass-to-Mass Conversion
How many grams of sodium hydroxide (NaOH) are needed to
completely react with 50.0 grams of sulfuric acid (H 2 SO 4 ) to form
sodium sulfate (Na 2 SO 4 ) and water?
Write the balanced equation.
2NaOH(aq) ϩ H 2 SO 4 (aq) 0 Na 2 SO 4 ϩ 2H 2 O(g)
Convert grams of sulfuric acid to moles NaOH.
50.0 g H 2 SO 4 ϫ
ϭ 0.510 mol H 2 SO 4
0.510 mol H 2 SO 4 ϫ
ϭ 1.02 mol NaOH
Calculate the mass of NaOH needed.
1.02 mol NaOH ϫ
ϭ 40.8 g NaOH
40.00 g NaOH
ᎏᎏ
1 mol NaOH
2 mol NaOH
ᎏᎏ
1 mol H 2 SO 4
1 mol H 2 SO 4
ᎏᎏ
98.09 g H 2 SO 4
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