Question

The mass fraction of an element present in a compound can be obtained by comparing the mass of the particular element present in 1 mole of the compound to the _____ mass of the compound.

Short answer

The mass fraction of an element present in a compound can be obtained by comparing the mass of the particular element present in 1 mole of the compound to the \(\textbf{molar mass}\) of the compound.

Step-by-step solution

Understanding mass fraction

Mass fraction is the ratio of the mass of a constituent (in this case, an element) present in a compound to the total mass of the compound. It is usually expressed as a percentage.

Identifying the missing term

To find the mass fraction of an element in a compound, we need to compare the mass of the particular element present in 1 mole of the compound to the total mass of the compound. The total mass of the compound is given by its molar mass. Therefore, the missing term in the statement is "molar."

Complete the statement

The mass fraction of an element present in a compound can be obtained by comparing the mass of the particular element present in 1 mole of the compound to the molar mass of the compound.

Key concepts

Molar Mass

Molar mass is a fundamental concept in chemistry that refers to the mass of one mole of a substance. In simpler terms, it is the mass of a given substance (an element or compound) divided by the amount of that substance expressed in moles. To calculate molar mass, we need to know the atomic or molecular weight of the substance. For compounds, this involves adding up the atomic masses of all the atoms in a single molecule of the compound.

Atomic masses of all elements are listed in the periodic table and are measured in atomic mass units (amu). However, when dealing with molar mass, we measure it in grams per mole (g/mol). For example, the molar mass of water (H₂O) is approximately 18 g/mol, calculated by adding the molar masses of two hydrogen atoms (1 g/mol each) and one oxygen atom (16 g/mol).

This concept becomes crucial when working out mass fractions since it lets us find the total mass of a compound we're analyzing. Once we have the molar mass, we can better understand how much of each element contributes to the compound as a whole, linking directly to the concept of percentage composition.

Percentage Composition

Percentage composition is crucial for understanding the makeup of a chemical compound. It gives us the proportion of each element within a compound in terms of percent mass. To find the percentage composition, we divide the mass of each element in one mole of a compound by the molar mass of the compound, and then multiply the result by 100%.

Calculating Percentage Composition

Let's take water again as our example. To calculate the percentage of hydrogen in water, we would take the molar mass of hydrogen (2 g, since there are two hydrogen atoms in one molecule of water), divide it by the molar mass of water (18 g/mol), and multiply by 100 to get the percentage. This calculation shows that hydrogen makes up approximately 11.11% of water by mass.

Understanding percentage composition is not only essential for stoichiometry in chemical reactions but also for confirming the empirical or molecular formula of a compound, identifying unknown substances, and providing insights into a compound's properties.

Mole Concept

The mole concept lays the foundation for quantifying substances in chemistry. A mole is a unit used to express amounts of a chemical substance and is defined as the number of particles (atoms, ions, or molecules) contained in 12 grams of carbon-12. This number, known as Avogadro's number, is approximately 6.022 x 10²³.

The mole allows chemists to count particles by weighing them. Since it's not feasible to count atoms or molecules individually due to their incredibly small size and vast numbers, we use moles to make this task manageable. By knowing the molar mass of a substance, we can convert between mass and moles, which is a cornerstone concept in stoichiometry and helps in balancing chemical equations. For instance, in a reaction involving hydrogen gas and oxygen gas to produce water, understanding the mole ratio allows for precise measurements of reactants to ensure the reaction goes to completion.

The mole concept seamlessly connects to the ideas of molar mass and percentage composition, as it provides the necessary link between the number of particles in a sample and the mass of those particles, forming the bridge needed for in-depth chemical analysis and understanding.