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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 90

What is the empirical formula of stannous fluoride, the first fluoride compound added to toothpaste to protect teeth against decay? Its mass percent composition is 24.25% F, 75.75% Sn.

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Identify the elements present in the compound: Fluorine (F) and Tin (Sn).
Convert the mass percentages to grams, assuming a 100 g sample: 24.25 g of F and 75.75 g of Sn.
Convert the masses to moles using the molar masses: \( \text{Molar mass of F} = 19.00 \, \text{g/mol} \) and \( \text{Molar mass of Sn} = 118.71 \, \text{g/mol} \).
Calculate the mole ratio by dividing the moles of each element by the smallest number of moles calculated.
Write the empirical formula using the mole ratio 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 of a compound represents the simplest whole-number ratio of the elements present in that compound. It is derived from the mass percent composition of the elements, allowing chemists to understand the basic composition without detailing the molecular structure.
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Mass Percent Composition

Mass percent composition indicates the percentage by mass 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.
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Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between mass and moles, which is necessary when calculating the empirical formula from mass percent composition, as it helps to determine the number of moles of each element present.
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