Ch.3 - Molecules, Compounds & Chemical Equations

Problem 88a

Chapter 3, Problem 88a

A chemist decomposes samples of several compounds; the masses of their constituent elements are listed. Calculate the empirical formula for each compound. a. 1.245 g Ni, 5.381 g I

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Determine the number of moles of each element by dividing the mass of each element by its molar mass. For Nickel (Ni), use its molar mass of approximately 58.69 g/mol, and for Iodine (I), use its molar mass of approximately 126.90 g/mol.

Calculate the moles of Nickel (Ni) using the formula: \( \text{moles of Ni} = \frac{1.245 \text{ g}}{58.69 \text{ g/mol}} \).

Calculate the moles of Iodine (I) using the formula: \( \text{moles of I} = \frac{5.381 \text{ g}}{126.90 \text{ g/mol}} \).

Determine the simplest whole number ratio of moles of Ni to moles of I by dividing each by the smallest number of moles calculated in the previous steps.

Write the empirical formula by using the whole number ratio as subscripts for each element in the compound.

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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 of each element and is crucial for understanding the composition of the compound. For example, if a compound contains 1 mole of element A and 2 moles of element B, its empirical formula would be AB2.

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 the mass of each element in a sample to moles, which allows for the determination of the ratio of elements in the empirical formula. For instance, the molar mass of nickel (Ni) is approximately 58.69 g/mol, and for iodine (I), it is about 126.90 g/mol.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It involves using balanced chemical equations to calculate the amounts of substances involved. In the context of finding an empirical formula, stoichiometry helps in determining the mole ratios of the elements based on their masses.

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