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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 52

What is the molecular weight of chloroform if 0.0275 mol weighs 3.28 g?

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Determine the formula for chloroform, which is CHCl3.
Calculate the molar mass of CHCl3 by adding the atomic masses of carbon (C), hydrogen (H), and chlorine (Cl). Carbon has an atomic mass of approximately 12.01 g/mol, hydrogen is about 1.01 g/mol, and chlorine is about 35.45 g/mol. Since there are three chlorine atoms, multiply the atomic mass of chlorine by three.
Add the atomic masses calculated in the previous step to find the total molecular weight of chloroform.
Use the formula: Molecular Weight = (Mass of the sample in grams) / (Number of moles). Plug in the values given in the problem: 3.28 grams for the mass and 0.0275 moles for the number of moles.
Solve the equation from the previous step to find the molecular weight of chloroform.

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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, or 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 weights of all atoms in a molecule. For chloroform (CHCl3), the molecular weight can be determined by adding the atomic weights of carbon (C), hydrogen (H), and chlorine (Cl) in the formula.
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Moles

A mole is a unit in chemistry that represents 6.022 x 10^23 entities, such as atoms or molecules. It allows chemists to count quantities of substances in a manageable way. The number of moles can be calculated using the formula: moles = mass (g) / molar mass (g/mol), which is essential for determining the molecular weight when given mass and moles.
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Conversion between Mass and Moles

The conversion between mass and moles is a fundamental concept in stoichiometry. It involves using the relationship between the mass of a substance and its molar mass to find the number of moles. In the context of the question, knowing the mass of chloroform and the number of moles allows for the calculation of its molecular weight using the formula: molecular weight = mass / moles.
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