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Ch.3 - Molecules and Compounds
Chapter 3, Problem 76a

Calculate the mass (in g) of each sample. a. 4.5×1025 O3 molecules

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1
Determine the number of moles of O3 molecules using Avogadro's number. Avogadro's number is approximately 6.022 \times 10^{23} molecules per mole. Use the formula: \text{moles} = \frac{\text{number of molecules}}{\text{Avogadro's number}}.
Calculate the molar mass of O3. Oxygen (O) has an atomic mass of approximately 16 g/mol. Since O3 consists of three oxygen atoms, multiply the atomic mass of oxygen by three.
Use the molar mass of O3 and the number of moles calculated in step 1 to find the mass. Apply the formula: \text{mass} = \text{moles} \times \text{molar mass}.
Ensure the units are consistent throughout the calculation. The final mass should be in grams (g).
Double-check your calculations for any possible errors to ensure accuracy.

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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). For ozone (O3), the molar mass can be calculated by summing the atomic masses of its constituent atoms: three oxygen atoms. This value is essential for converting between the number of molecules and mass.
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Avogadro's Number

Avogadro's number, approximately 6.022 x 10^23, is the number of particles (atoms, molecules, etc.) in one mole of a substance. This constant allows chemists to relate the macroscopic scale of substances to the microscopic scale, enabling calculations involving the number of molecules and moles.
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Conversion from Molecules to Grams

To convert the number of molecules to grams, one must first determine the number of moles by dividing the number of molecules by Avogadro's number. Then, multiply the number of moles by the molar mass of the substance. This two-step process is crucial for accurately calculating the mass of a sample based on its molecular count.
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