Problem 133 - Chemistry The Science in Context

Question

The solar wind is made up of ions, mostly protons, flowing out from the sun at about \(400 \mathrm{km} / \mathrm{s} .\) Near Earth, each cubic kilometer of interplanetary space contains, on average, \(6 \times 10^{15}\) solar-wind ions. How many moles of ions are in a cubic kilometer of near-Earth space?

Step-by-Step Solution

Answer

Answer: Approximately 9.964x10⁻⁹ moles.

Step 1: Identify given values

We are given: 1. The number of solar-wind ions per cubic kilometer: \(6 \times 10^{15}\) 2. Avogadro's number: \(6.022\times10^{23}\) ions/mole

Step 2: Calculate the number of moles

Divide the number of ions per cubic kilometer by Avogadro's number: Number of moles = \(\frac{6\times10^{15} \text{ ions}}{6.022\times10^{23} \text{ ions/mole}}\)

Step 3: Simplify and find the result

Simplify the fraction to obtain the number of moles: Number of moles = \(\frac{6\times10^{15}}{6.022\times10^{23}}\) = \(9.964\times10^{-9}\) moles So, there are approximately \(9.964\times10^{-9}\) moles of ions in a cubic kilometer of near-Earth space.

Key Concepts

Avogadro's number

Understanding Avogadro's number is crucial when dealing with quantities in chemistry. It's akin to the concept of a dozen eggs, but instead of 12, we're talking about a much larger count. Specifically, Avogadro's number is approximated to be \(6.022 \times 10^{23}\). This vast quantity is the number of units, usually atoms or molecules, in one mole of any substance.

When we reference Avogadro's number, we are referring to the bridge between the microscopic world of atoms and the macroscopic world of grams and liters that we interact with on a daily basis. It allows chemists and students alike to count out particles by weighing out a mass. Each element's atomic or molecular mass in grams corresponds to one mole, which always contains Avogadro's number of those particles, whether they are ions, atoms, or molecules.

In our exercise, Avogadro's number is used to convert the sheer number of solar wind ions in a cubic kilometer of space into the more manageable unit of moles, which is a standard unit in chemistry for expressing quantities of particles or entities.

Mole concept

The mole concept is a fundamental pillar in the study of chemistry, serving as a bridge between the atomic scale and the macroscopic world. It represents a fundamental unit in the International System of Units (SI) for the amount of substance. One mole of any substance contains exactly Avogadro's number of entities, which can be atoms, molecules, ions, or even electrons.

What makes the mole such a useful unit is its universal applicability; it allows chemists to easily convert between the number of particles and the mass of a substance because the mass of one mole of a substance is equal to its relative formula mass in grams. For instance, if we were given the mass of a substance, we could easily work out the number of moles by dividing the mass by the molar mass.

This concept is central to the exercise, where we use the mole concept to quantify ions in space. It provides the means to coherently translate a physically uncountable number of solar wind ions into an expressive and quantifiable amount expressed by moles.

Solar wind ions

Solar wind ions are charged particles emitted by the upper atmosphere of the Sun. Comprised mostly of electrons and protons, the solar wind is a stream of ionized gas that flows through the solar system at high speeds, reaching around \(400 \mathrm{km/s}\).

Understanding the nature of solar wind ions is not only essential in space physics but also in understanding interplanetary conditions. These ions are capable of creating the beautiful auroras and also have the potential to disrupt communications and navigation satellites, as well as power grids on Earth. In our context, knowing the density of these ions in a given volume of space allows us to calculate the number of ions, and subsequently, the number of moles in that space following the mole concept.

Stoichiometry

Stoichiometry comes from the Greek words 'stoicheion' (element) and 'metron' (measure), which essentially means measuring elements. In chemistry, stoichiometry is the quantification of substances involved in chemical reactions using balanced equations and the mole concept. It allows chemists to predict the quantities of reactants and products in a given reaction.

Although our current exercise does not involve a chemical reaction, stoichiometry's principles are universally applicable to any situation that calls for measuring the quantities of entities. It involves the use of conversion factors, such as Avogadro's number, to switch between units - in this case, from the number of ions to moles. It's a crucial tool for understanding and predicting the outcome of chemical processes and conversions, making chemistry a precise and predictable science.