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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 12

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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Key Concepts

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

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It is derived from the percentage composition of each element, allowing chemists to understand the basic composition of a substance without detailing the actual number of atoms in a molecule.
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Empirical vs Molecular Formula

Mole Concept

The mole concept is a fundamental principle in chemistry that relates the mass of a substance to the number of particles it contains. One mole of any substance contains Avogadro's number (approximately 6.022 x 10²³) of entities, whether they are atoms, molecules, or ions, facilitating conversions between mass and number of particles.
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Percentage Composition

Percentage composition refers to the mass percentage of each element in a compound. It is calculated by dividing the mass of each element by the total mass of the compound and multiplying by 100. This information is crucial for determining the empirical formula, as it provides the necessary data to find the simplest ratio of elements.
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Related Practice
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
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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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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Textbook Question
Which of the following compounds is incorrectly named? (LO 2.23–2.25) (a) CaO; calcium oxide (b) FeBr2; iron dibromide (c) N2O5; dinitrogen pentoxide (d) CrO3; chromium(VI) oxide
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