Ch.3 - Chemical Reactions and Reaction Stoichiometry

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 29b

Chapter 3, Problem 29b

(a) Write 'true' or 'false' for each statement. (b) A mole of water has a mass of 18.0 g.

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(a) To determine if a statement is 'true' or 'false', evaluate the accuracy of the statement based on known chemical principles or data.

(b) Understand that a mole is a unit in chemistry that represents Avogadro's number (approximately 6.022 x 10^23) of particles, atoms, or molecules.

(b) Calculate the molar mass of water (H2O) by adding the atomic masses of its constituent elements: 2 hydrogen atoms and 1 oxygen atom.

(b) The atomic mass of hydrogen is approximately 1.0 g/mol, and the atomic mass of oxygen is approximately 16.0 g/mol.

(b) Add the atomic masses: (2 x 1.0 g/mol) + (1 x 16.0 g/mol) to find the molar mass of water, which should confirm the given mass of a mole of water.

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Key Concepts

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

Mole Concept

The mole is a fundamental unit in chemistry that quantifies the amount of substance. One mole contains approximately 6.022 x 10^23 entities, such as atoms or molecules. This concept allows chemists to convert between the mass of a substance and the number of particles it contains, facilitating stoichiometric calculations.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For water (H2O), the molar mass is calculated by summing the atomic masses of its constituent elements: hydrogen (1.01 g/mol) and oxygen (16.00 g/mol), resulting in a total of approximately 18.0 g/mol. This value is crucial for converting between mass and moles.

Density and Mass Relationships

Understanding the relationship between mass, volume, and density is essential in chemistry. Density is defined as mass per unit volume (d = m/V). For water, knowing its density (1 g/cm³) helps confirm that a mole of water, which has a mass of 18.0 g, occupies a volume of about 18.0 cm³, reinforcing the connection between these properties.

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