Ch.3 - Molecules and Compounds

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.3 - Molecules and Compounds

Problem 72d

Chapter 3, Problem 72d

Determine the number of moles (of molecules or formula units) in each sample. d. 195 kg CaO

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Identify the molar mass of CaO. Calcium (Ca) has an atomic mass of approximately 40.08 g/mol and Oxygen (O) has an atomic mass of approximately 16.00 g/mol. Add these values to find the molar mass of CaO.

Convert the mass of CaO from kilograms to grams to align with the units of molar mass. Recall that 1 kg equals 1000 grams.

Use the formula for the number of moles, which is the mass of the substance (in grams) divided by the molar mass of the substance (in g/mol).

Substitute the mass of CaO in grams and the molar mass of CaO in g/mol into the formula to calculate the number of moles.

Ensure the final answer is expressed in moles, which is the unit for the amount of substance.

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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). It is calculated by summing the atomic masses of all the atoms in a molecule or formula unit. For calcium oxide (CaO), the molar mass is approximately 56.08 g/mol, which is essential for converting between mass and moles.

Moles and Avogadro's Number

A mole is a unit in chemistry that represents 6.022 x 10²³ entities, such as atoms or molecules. This number, known as Avogadro's number, allows chemists to count particles by weighing them. Understanding moles is crucial for stoichiometric calculations, as it provides a bridge between the mass of a substance and the number of particles it contains.

Conversion between Mass and Moles

To determine the number of moles from a given mass, the formula used is: moles = mass (g) / molar mass (g/mol). This conversion is fundamental in chemistry, allowing for the quantification of reactants and products in chemical reactions. In the case of 195 kg of CaO, converting kilograms to grams and then applying the molar mass will yield the number of moles present in the sample.

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Mass and Moles Conversion

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