Question

How many oxygen atoms are in each set? (a) four dinitrogen monoxide molecules (b) two calcium carbonate formula units (c) three sulfur dioxide molecules (d) five perchlorate ions

Short answer

(a) 4 oxygen atoms, (b) 6 oxygen atoms, (c) 6 oxygen atoms, (d) 20 oxygen atoms.

Step-by-step solution

Determine the oxygen content of a dinitrogen monoxide molecule

A dinitrogen monoxide molecule has the formula N2O, indicating that there is one oxygen atom per molecule. Therefore, we need to multiply the number of molecules by the number of oxygen atoms per molecule.

Calculate the total number of oxygen atoms in four dinitrogen monoxide molecules

Since there is one oxygen atom per dinitrogen monoxide molecule, four molecules will contain a total of 4 x 1 = 4 oxygen atoms.

Determine the oxygen content of a calcium carbonate formula unit

A calcium carbonate formula unit, CaCO3, contains three oxygen atoms. To find the total number of oxygen atoms in two formula units, we will multiply the number of formula units by the number of oxygen atoms per formula unit.

Calculate the total number of oxygen atoms in two calcium carbonate formula units

There are 3 oxygen atoms in a single calcium carbonate formula unit. Therefore, two units will contain 2 x 3 = 6 oxygen atoms.

Determine the oxygen content of a sulfur dioxide molecule

A sulfur dioxide molecule, SO2, contains two oxygen atoms. To find the total number of oxygen atoms in three molecules, we will multiply the number of molecules by the number of oxygen atoms per molecule.

Calculate the total number of oxygen atoms in three sulfur dioxide molecules

There are 2 oxygen atoms in a single sulfur dioxide molecule. Hence, three molecules will contain 3 x 2 = 6 oxygen atoms.

Determine the oxygen content of a perchlorate ion

A perchlorate ion, ClO4-, contains four oxygen atoms. To find the total number of oxygen atoms in five ions, we multiply the number of ions by the number of oxygen atoms per ion.

Calculate the total number of oxygen atoms in five perchlorate ions

As there are 4 oxygen atoms in a single perchlorate ion, five ions will contain 5 x 4 = 20 oxygen atoms.

Key concepts

Molecular Composition

Understanding molecular composition is fundamental in grasping how substances are structured. It refers to the type and number of atoms that make up a molecule. For example, in water (H₂O), the molecular composition is two hydrogen atoms and one oxygen atom. We use the molecular composition to understand the properties of substances and predict how they will react with others. When solving problems involving molecular composition, it's essential to carefully identify the components of each molecule and then calculate the atoms' counts accordingly.

Let's improve upon the exercise solution by highlighting that the unique makeup of each molecule or ion directly influences the total count of a specific atom in a collection of molecules. Like in the textbook solution, identifying the number of oxygen atoms present in one unit of the molecule or ion is the first step to understanding the composition of that substance.

Chemical Formulas

The chemical formula of a substance represents the elements that make it up and their respective quantities. Formulas can range from simple ones like NaCl, denoting table salt made up of one sodium (Na) and one chlorine (Cl) atom, to more complex ones involving several atoms, as seen in organic compounds. In our example, we've seen formulas like N₂O and CaCO₃.

To better interpret these formulas, focus on the subscript numbers since they indicate the number of atoms of each element within the compound. If there is no subscript, it implies just one atom of that element. Understanding chemical formulas is indispensable when calculating the amounts of individual atoms, as was necessary in the textbook solutions to count oxygen atoms in various compounds.

Stoichiometry

Stoichiometry is the section of chemistry that pertains to the calculation of the quantities of reactants and products in chemical reactions. It is essential when predicting yields, determining reactant proportions, and more. Stoichiometry relies on the balanced chemical equation and applies the laws of conservation of mass and constant proportions.

In practice, we use stoichiometric coefficients from the balanced equation to determine the proportion of molecules or formula units involved. Understanding stoichiometry can help with exercises like the textbook problem, making it evident why multiplying the number of molecules by the number of oxygen atoms in one molecule gave us the total oxygen content in a set of molecules. This approach is a practical application of the stoichiometric principles.

Avogadro's Number

Avogadro's number, typically noted as 6.022 x 10²³, is defined as the number of constituent particles, usually atoms or molecules, contained in one mole of a substance. This constant is named after Amedeo Avogadro, an Italian scientist, and is crucial for converting between the number of atoms or molecules and the amount of substance in moles.

Even though Avogadro's number wasn't used explicitly in the solution of the exercise provided, understanding it is crucial when dealing with larger scales beyond a few molecules. For instance, if the problem asked for the number of oxygen atoms in two moles of calcium carbonate (CaCO₃), we would use Avogadro's number to find that there are 2 moles x 3 atoms/molecule x 6.022 x 10²³ atoms/mole = 3.6132 x 10²⁴ oxygen atoms. It's these types of conversions that embody the importance of Avogadro's number in chemistry.