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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 87c

Calculate the mass percent composition of each of the following substances. (c) Prussian blue, an ink pigment: Fe4[Fe(CN)6]3

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1
Identify the chemical formula of Prussian blue: Fe_4[Fe(CN)_6]_3.
Calculate the molar mass of each element in the compound: Fe, C, N.
Determine the number of each type of atom in the formula: 7 Fe, 18 C, 18 N.
Calculate the total molar mass of the compound by summing the contributions of all atoms.
Calculate the mass percent of each element by dividing the total mass of each element by the molar mass of the compound and multiplying by 100.

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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 calculate the molar mass of a compound, you sum the atomic masses of all the atoms in its chemical formula. For Prussian blue, you would need to account for the contributions of iron (Fe), carbon (C), and nitrogen (N) from its formula Fe4[Fe(CN)6]3.
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Mass Percent Composition

Mass percent composition refers to the percentage by mass of each element in a compound. It is calculated by dividing the mass of each element in one mole of the compound by the total molar mass of the compound, then multiplying by 100. This concept is essential for understanding the distribution of elements within a compound, such as Prussian blue.
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Chemical Formula Interpretation

Interpreting a chemical formula involves understanding the ratios and types of atoms present in a compound. In the case of Prussian blue, the formula Fe4[Fe(CN)6]3 indicates that there are multiple iron atoms and cyanide groups. Recognizing how to break down the formula into its constituent parts is crucial for accurate calculations of molar mass and mass percent composition.
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