Ch.3 - Mass Relationships in Chemical Reactions

Problem 11

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Chapter 3, Problem 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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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

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.

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.

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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Related Practice

Textbook Question

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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Textbook Question

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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Textbook Question

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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Textbook Question

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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Textbook Question

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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Textbook Question

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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