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Ch.3 - Molecules, Compounds & Chemical Equations
All textbooksTro 4th EditionCh.3 - Molecules, Compounds & Chemical EquationsProblem 68b,c
Chapter 3, Problem 68b,c

Calculate the mass (in g) of each sample. b. 9.85×1019 CCl2F2 molecules c. 1 water molecule

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Determine the molar mass of CCl2F2 by adding the atomic masses of carbon (C), chlorine (Cl), and fluorine (F). The atomic masses are approximately: C = 12.01 g/mol, Cl = 35.45 g/mol, and F = 19.00 g/mol. Since there are two chlorine and two fluorine atoms, the molar mass of CCl2F2 is calculated as: Molar mass = 12.01 g/mol + (2 \times 35.45 g/mol) + (2 \times 19.00 g/mol).
Convert the number of CCl2F2 molecules to moles using Avogadro's number, which is approximately 6.022 \times 10^{23} molecules/mol. Use the formula: Moles = Number of molecules / Avogadro's number.
Calculate the mass of the CCl2F2 sample by multiplying the number of moles by the molar mass of CCl2F2. Use the formula: Mass (g) = Moles \times Molar mass (g/mol).
Ensure the units are consistent throughout the calculation to avoid any errors in the final result.
Double-check each calculation step for accuracy to ensure the correct mass is determined.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Weight

Molecular weight is the mass of a molecule calculated as the sum of the atomic weights of all atoms in the molecule. For CCl2F2, the molecular weight can be determined by adding the atomic weights of carbon (C), chlorine (Cl), and fluorine (F) based on their respective quantities in the formula. This value is essential for converting between moles and grams.
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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 number of molecules to the amount of substance in moles, which is crucial for calculations involving mass and molecular quantities.
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Conversion from Molecules to Grams

To calculate the mass of a sample from the number of molecules, one must first convert the number of molecules to moles using Avogadro's number. Then, the number of moles is multiplied by the molecular weight of the substance to find the mass in grams. This process is fundamental in stoichiometry and quantitative chemistry.
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