Determine the percentage composition of the substance.

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Identify the chemical formula of the substance. This will provide the types and numbers of atoms present in the compound.

Calculate the molar mass of the compound by summing the atomic masses of all the atoms in the formula. Use the periodic table to find the atomic masses of each element.

For each element in the compound, calculate the total mass contributed by that element. Multiply the atomic mass of the element by the number of atoms of that element in the formula.

Determine the percentage composition of each element by dividing the total mass of the element by the molar mass of the compound, then multiply by 100 to convert to a percentage.

Repeat the calculation for each element in the compound to find the complete percentage composition of the substance.

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 molecule. Understanding molar mass is essential for determining the percentage composition, as it provides the basis for converting between mass and moles.

Percentage Composition

Percentage composition refers to the mass percentage 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 crucial for understanding the relative amounts of different elements in a substance.

Empirical and Molecular Formulas

Empirical formulas represent the simplest whole-number ratio of elements in a compound, while molecular formulas indicate the actual number of atoms of each element in a molecule. Knowing how to derive these formulas is important for calculating percentage composition, as it helps identify the elements involved and their respective contributions to the total mass.

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Empirical vs Molecular Formula

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Textbook Question

The graph below shows the change in pressure as the temperature increases for a 1-mol sample of a gas confined to a 1-L container. The four plots correspond to an ideal gas and three real gases: CO2, N2, and Cl2. (a) At room temperature, all three real gases have a pressure less than the ideal gas. Which van der Waals constant, a or b, accounts for the influence intermolecular forces have in lowering the pressure of a real gas?

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Textbook Question

The graph below shows the change in pressure as the temperature increases for a 1-mol sample of a gas confined to a 1-L container. The four plots correspond to an ideal gas and three real gases: CO2, N2, and Cl2. (b) Use the van der Waals constants in Table 10.3 to match the labels in the plot (A, B, and C) with the respective gases 1CO2, N2, and Cl22.

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Which of the following statements is false? (a) Gases are far less dense than liquids. (b) Gases are far more compressible than liquids. (c) Because liquid water and liquid carbon tetrachloride do not mix, neither do their vapors. (d) The volume occupied by a gas is determined by the volume of its container.

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