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Ch.3 - Chemical Reactions and Reaction Stoichiometry
All textbooksBrown 14th EditionCh.3 - Chemical Reactions and Reaction StoichiometryProblem 25a
Chapter 3, Problem 25a

Calculate the percentage by mass of oxygen in the following compounds: (a) vanillin, C8H8O3

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1
Determine the molar mass of vanillin, \( C_8H_8O_3 \), by adding the atomic masses of all the atoms in the formula. Use the periodic table to find the atomic masses: Carbon (C) is approximately 12.01 g/mol, Hydrogen (H) is approximately 1.01 g/mol, and Oxygen (O) is approximately 16.00 g/mol.
Calculate the total mass of oxygen in the compound by multiplying the number of oxygen atoms (3) by the atomic mass of oxygen (16.00 g/mol).
Add the masses of all the atoms in the compound to find the total molar mass of vanillin.
Use the formula for percentage by mass: \( \text{Percentage by mass of oxygen} = \left( \frac{\text{Total mass of oxygen}}{\text{Molar mass of vanillin}} \right) \times 100 \% \).
Substitute the values obtained in the previous steps into the formula to calculate the percentage by mass of oxygen in vanillin.

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Key Concepts

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

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all the atoms in a chemical formula. For example, in vanillin (C8H8O3), the molar mass is determined by adding the contributions from carbon, hydrogen, and oxygen atoms based on their respective quantities.
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Percentage by Mass

Percentage by mass is a way to express the concentration of a particular element in a compound. It is calculated by dividing the mass of the element by the total mass of the compound and then multiplying by 100. This calculation helps in understanding the composition of compounds and is essential for stoichiometric calculations in chemistry.
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Chemical Formula Interpretation

Interpreting a chemical formula involves understanding the types and numbers of atoms present in a compound. In the case of vanillin (C8H8O3), the formula indicates there are 8 carbon atoms, 8 hydrogen atoms, and 3 oxygen atoms. This information is crucial for calculating the molar mass and subsequently the percentage by mass of each element in the compound.
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Related Practice
Textbook Question

Balance the following equations and indicate whether they are combination, decomposition, or combustion reactions: (a) NaClO3(s) → NaCl(s) + O2(g) (b) NH4OH(aq) → H2O(l) + NH3(g) (c) K(s) + Cl2(g) → KCl(s) (d) C2H5OH(l) + O2(g) → CO2(g) + H2O(l)

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