Check your learning: self-test

Write a balanced equation for the decomposition of ammonium nitrate to form molecular nitrogen, molecular oxygen, and water. (Hint: Balance oxygen last, since it is present in more than one molecule on the right side of the equation.)
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[latex]2{\text{NH}}_{4}{\text{NO}}_{3}\rightarrow 2{\text{N}}_{2}+{\text{O}}_{2}+4{\text{H}}_{2}\text{O}[/latex]
Acetaminophen, C₈H₉NO₂, is a covalent compound and the active ingredient in several popular nonprescription pain medications, such as Tylenol. What is the molecular mass (amu) for this compound?
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151.16 amu
Calcium phosphate, Ca₃(PO₄)₂, is an ionic compound and a common anti-caking agent added to food products. What is the formula mass (amu) of calcium phosphate?
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310.18 amu
Beryllium is a light metal used to fabricate transparent X-ray windows for medical imaging instruments. How many moles of Be are in a thin-foil window weighing 3.24 g?
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0.360 mol
What is the mass of 2.561 mol of gold?
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504.4 g
A prospector panning for gold in a river collects 15.00 g of pure gold. How many Au atoms are in this quantity of gold?
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[latex]4.586\times {10}^{22}\text{Au atoms}[/latex]
How many moles of sucrose, C₁₂H₂₂O₁₁, are in a 25-g sample of sucrose?
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0.073 mol
What is the mass of 0.443 mol of hydrazine, N₂H₄?
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14.2 g
How many C₄H₁₀ molecules are contained in 9.213 g of this compound? How many hydrogen atoms?
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[latex]9.545\times {10}^{22}\text{molecules }{\text{C}}_{4}{\text{H}}_{10}\text{; }9.545\times {10}^{23}\text{ atoms H}[/latex]
How many moles of Ca(OH)₂ are required to react with 1.36 mol of H₃PO₄ to produce Ca₃(PO₄)₂ according to the equation [latex]3\text{Ca}{\text{(}\text{OH}\text{)}}_{2}+2{\text{H}}_{3}{\text{PO}}_{4}\rightarrow{\text{Ca}}_{3}{\text{(}{\text{PO}}_{4}\text{)}}_{2}+6{\text{H}}_{2}\text{O}[/latex]?
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2.04 mol
many NH₃ molecules are produced by the reaction of 4.0 mol of Ca(OH)₂ according to the following equation:
[latex]{\text{(}{\text{NH}}_{4}\text{)}}_{2}{\text{SO}}_{4}+\text{Ca}{\text{(}\text{OH}\text{)}}_{2}\rightarrow 2{\text{NH}}_{3}+{\text{CaSO}}_{4}+2{\text{H}}_{2}\text{O.}[/latex]

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4.8 × 10²⁴ NH₃ molecules
What mass of gallium oxide, Ga₂O₃, can be prepared from 29.0 g of gallium metal? The equation for the reaction is [latex]4\text{Ga}+3{\text{O}}_{2}\rightarrow 2{\text{Ga}}_{2}{\text{O}}_{3}\text{.}[/latex]
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39.0 g
What mass of CO is required to react with 25.13 g of Fe₂O₃ according to the equation [latex]{\text{Fe}}_{2}{\text{O}}_{3}+3\text{CO}\rightarrow 2\text{Fe}+3{\text{CO}}_{2}?[/latex]
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13.22 g
A 24.81-g sample of a gaseous compound containing only carbon, oxygen, and chlorine is determined to contain 3.01 g C, 4.00 g O, and 17.81 g Cl. What is this compound’s percent composition?
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12.1% C, 16.1% O, 71.8% Cl
To three significant digits, what is the mass percentage of iron in the compound Fe₂O₃?
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69.9% Fe
What is the empirical formula of a compound if a sample contains 0.130 g of nitrogen and 0.370 g of oxygen?
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N₂O₅
What is the empirical formula of a compound containing 40.0% C, 6.71% H, and 53.28% O?
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CH₂O
What is the molecular formula of a compound with a percent composition of 49.47% C, 5.201% H, 28.84% N, and 16.48% O, and a molecular mass of 194.2 amu?
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C₈H₁₀N₄O₂
How many moles of Al₂O₃ will be produced when 23.9 g of H₂O are reacted according to this chemical equation?

[latex]2AlCl_3 + 3H_2O(ℓ) → Al_2O_3 + 6HCl(g)[/latex]

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[latex]0.442 mol[/latex][/hidden-answer
How many grams of N₂ are needed to produce 2.17 mol of NH₃ when reacted according to this chemical equation?

[latex]N_2(g) + 3H_2(g) → 2NH_3(g)[/latex]

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30.4 g (Note: here we go from a product to a reactant, showing that mole-mass problems can begin and end with any substance in the chemical equation.)

Chapter 4-Stoichiometry and The Mole