Textbook Question
Write a ratio showing the relationship between the molar amounts of each element for each compound. (See Appendix IIA for color codes.) (b)
Ch.3 - Molecules and Compounds
Chapter 3, Problem 89a
Calculate the empirical formula for each stimulant based on its elemental mass percent composition.
a. nicotine (found in tobacco leaves): C 74.03%, H 8.70%, N 17.27%
b. caffeine (found in coffee beans): C 49.48%, H 5.19%, N 28.85%, O 16.48%
Verified step by step guidance1
Step 1: Assume you have 100 grams of nicotine, which makes the mass of each element equal to its percentage.
Step 2: Convert the mass of each element to moles by dividing by its atomic mass: C (12.01 g/mol), H (1.008 g/mol), N (14.01 g/mol).
Step 3: Determine the mole ratio by dividing each element's mole value by the smallest number of moles calculated in Step 2.
Step 4: If necessary, multiply the mole ratios by a whole number to get whole numbers for each element.
Step 5: Write the empirical formula using the whole number mole ratios as subscripts for each element.
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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 percent composition of each element, which indicates how much of each element is present in a sample. For example, if a compound contains 50% carbon and 50% oxygen, its empirical formula would be CO, reflecting the 1:1 ratio.
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Empirical vs Molecular Formula
Mass Percent Composition
Mass percent composition is the percentage by mass of each element in a compound relative to the total mass of the compound. It is calculated by dividing the mass of each element by the total mass and multiplying by 100. This information is crucial for determining the empirical formula, as it provides the necessary data to find the ratio of elements.
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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 10^23) of entities, whether they are atoms, molecules, or ions. This concept is essential for converting mass percent compositions into moles, which are then used to derive the empirical formula.
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Related Practice
Textbook Question
A chemist decomposes samples of several compounds; the masses of their constituent elements are listed. Calculate the empirical formula for each compound. b. 2.677 g Ba, 3.115 g Br
Textbook Question
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Textbook Question
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