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Ch.3 - Mass Relationships in Chemical Reactions
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Non è quello che usi tu?Cambia libro di testo
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Capitolo 3, Problema 3

The ball-and-stick molecular model is a representation of caf-feine. Calculate the molecular weight of caffeine. (Gray = C, red = O, blue = N, ivory = H.) (LO 3.3)
Ball-and-stick model of caffeine showing atoms: gray for carbon, red for oxygen, blue for nitrogen, ivory for hydrogen.
(a) 194.2 (b) 182.2 (c) 192.2 (d) 180.2

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Count the number of each type of atom in the caffeine molecule. Identify the colors: Gray = Carbon (C), Red = Oxygen (O), Blue = Nitrogen (N), Ivory = Hydrogen (H).
Determine the atomic masses of each element: Carbon (C) = 12.01 g/mol, Oxygen (O) = 16.00 g/mol, Nitrogen (N) = 14.01 g/mol, Hydrogen (H) = 1.01 g/mol.
Multiply the number of each type of atom by its atomic mass to find the total mass contribution of each element.
Sum the total mass contributions of all elements to find the molecular weight of caffeine.
Compare the calculated molecular weight with the given options (a) 194.2, (b) 182.2, (c) 192.2, (d) 180.2 to determine the correct answer.

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Molecular Weight

Molecular weight, or molar mass, is the sum of the atomic weights of all atoms in a molecule, expressed in grams per mole (g/mol). It is calculated by multiplying the number of each type of atom by its atomic weight and summing these values. For caffeine, which contains carbon, hydrogen, nitrogen, and oxygen, the molecular weight is essential for understanding its chemical properties and behavior.
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Weight Conversion Example

Ball-and-Stick Model

The ball-and-stick model is a three-dimensional representation of molecular structures, where balls represent atoms and sticks represent the bonds between them. This model helps visualize the arrangement of atoms in a molecule, including bond angles and distances. In the case of caffeine, the model illustrates the connectivity and spatial orientation of carbon, hydrogen, nitrogen, and oxygen atoms.
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Bohr Model of the Atom

Chemical Composition of Caffeine

Caffeine is an organic compound with the chemical formula C8H10N4O2, indicating it contains 8 carbon (C), 10 hydrogen (H), 4 nitrogen (N), and 2 oxygen (O) atoms. Understanding its chemical composition is crucial for calculating its molecular weight and for studying its biological effects and interactions. Each atom type contributes differently to the overall molecular weight, influencing its properties.
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Matter Composition
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