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Ch.3 - Mass Relationships in Chemical Reactions
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.3 - Mass Relationships in Chemical ReactionsProblema 11
Capitolo 3, Problema 11

What is the percent composition by mass of Mn in potas-sium permanganate, KMnO4? (LO 3.10) (a) 22.6% (b) 34.8% (c) 49.9% (d) 54.9%

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Determine the molar mass of each element in potassium permanganate (KMnO_4): K, Mn, and O.
Calculate the molar mass of KMnO_4 by adding the molar masses of all the atoms in the formula.
Identify the molar mass of Mn from the periodic table.
Calculate the percent composition by mass of Mn using the formula: (molar mass of Mn / molar mass of KMnO_4) * 100%.
Compare the calculated percent composition with the given options to identify the correct answer.

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Molar Mass Calculation

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To find the molar mass of a compound, you sum the atomic masses of all the atoms in its chemical formula. For potassium permanganate (KMnO4), you would calculate the molar mass by adding the atomic masses of potassium (K), manganese (Mn), and four oxygen (O) atoms.
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Molar Mass Calculation Example

Percent Composition

Percent composition by mass refers to the percentage of a specific element in a compound relative to the total mass of the compound. It is calculated using the formula: (mass of the element in 1 mole of the compound / molar mass of the compound) x 100%. This concept is essential for determining how much of a compound's mass is contributed by a particular element.
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Mass Percent Calculation

Stoichiometry

Stoichiometry is the area of chemistry that deals with the relationships between the quantities of reactants and products in chemical reactions. It allows chemists to predict the amounts of substances consumed and produced in a reaction. Understanding stoichiometry is crucial for accurately calculating percent compositions and performing other quantitative analyses in chemistry.
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Stoichiometry Concept
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Lactic acid forms in muscle tissue after strenuous exercise. Elemental analysis shows that lactic acid is 40.0% carbon, 6.71% hydrogen, and 53.3% oxygen by mass. If the molec-ular weight of lactic acid is 90.08, what is the molecular for-mula? (LO 3.11) (a) CH2O (b) C3H6O3 (c) C4H8O4 (d) C4H10O2
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Combustion analysis is performed on 0.50 g of a hydrocar-bon and 1.55 g of CO2, and 0.697 g of H2O are produced. The mass spectrum for the hydrocarbon is provided below. What is the molecular formula? (LO 3.12 and 3.13)

(a) C5H11 (b) C8H18 (c) C11H10 (d) C10H22

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Silver sulfide, the tarnish on silverware, comes from the reaction of silver metal with hydrogen sulfide (H2S).The unbalanced equation is: Ag + H2S + O2 --> Ag2S + H2O Unbalanced If the reaction was used intentionally to prepare Ag2S, how many grams would be formed from 496 g of Ag, 80.0 g of H2S, and excess O2 if the reaction takes place in 90% yield? (LO 3.9) (a) 525 g (b) 1139 g (c) 583 g (d) 1025

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If 2.00 moles of nitrogen and 5.50 moles of hydrogen are placed in a reaction vessel and react to form ammonia, what is the theoretical yield of ammonia (NH3)? (LO 3.8) N2(g) + 3 H2(g) --> 2 NH3(g) (a) 31.2 g (b) 62.3 g (c) 93.7 g (d) 34.1
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Dimethylhydrazine, a colorless liquid used as a rocket fuel, is 40.0% C, 13.3% H, and 46.7% N. What is the empirical formula? (LO 3.11) (a) CH4N9 (b) CH2N (c) C2H4N (d) C2H5N2

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The diagram represents a mixture of AB2 and B2 before it reacts to form AB3. (Red spheres = A, blue spheres = B.) Which reactant is limiting, and how many AB3 molecules are formed? (LO 3.7)

(a) B2 is limiting, and 10 molecules of AB3 are formed. (b) B2 is limiting, and 4 molecules of AB3 are formed. (c) AB2 is limiting, and 6 molecules of AB3 are formed. (d) AB2 is limiting, and 4 molecules of AB3 are formed
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