The exact mass of iron (Fe) in one mole of iron(III) chloride (FeCl₃) is 55.845 grams.
In chemistry, a mole is a unit used to express the amount of a chemical substance. It is defined as containing exactly 6.022 × 10²³ elementary entities (such as atoms, molecules, or ions). The molar mass of a substance is the mass in grams of one mole of that substance.
Understanding Molar Mass and Chemical Formulas
The chemical formula FeCl₃ indicates that one molecule (or formula unit) of iron(III) chloride contains one atom of iron (Fe) and three atoms of chlorine (Cl). Consequently, one mole of FeCl₃ contains one mole of iron atoms and three moles of chlorine atoms.
The molar mass of a compound is the sum of the atomic masses of all the atoms in its chemical formula. For FeCl₃, the molar mass is provided as 162.2 g/mol. This value is derived from the sum of the atomic mass of one iron atom and three chlorine atoms.
Calculating the Mass of Iron in FeCl₃
To find the mass of iron in one mole of FeCl₃, we simply need to consider the atomic mass of iron, as there is one mole of iron atoms present in one mole of FeCl₃.
- Identify the chemical formula: FeCl₃. This tells us there is 1 atom of Fe per formula unit.
- Determine the molar mass of Iron (Fe): The accepted atomic mass of iron is approximately 55.845 grams per mole (g/mol). You can verify this value from a reliable source like the National Institute of Standards and Technology (NIST).
- Relate to the compound: Since one mole of FeCl₃ contains exactly one mole of Fe atoms, the mass contribution of iron to the total molar mass of FeCl₃ is simply the molar mass of Fe itself.
The breakdown of the molar mass of FeCl₃ is as follows:
| Element | Number of Moles per Mole of FeCl₃ | Molar Mass (g/mol) | Total Mass Contribution (g) |
|---|---|---|---|
| Iron (Fe) | 1 | 55.845 | 55.845 |
| Chlorine (Cl) | 3 | 35.453 | 106.359 (3 × 35.453) |
| Total | 162.204 |
As shown in the table, the mass of iron (Fe) specifically contributes 55.845 grams to every 162.2 grams of FeCl₃.
Why is this important?
Understanding the individual mass contributions of elements within a compound is fundamental in chemistry for several reasons:
- Stoichiometry: This knowledge is crucial for calculating the precise amounts of reactants and products in chemical reactions. For instance, if you need a specific mass of iron for a reaction, knowing its proportion in FeCl₃ allows you to calculate how much FeCl₃ is required.
- Chemical Analysis: It helps in determining the elemental composition of unknown samples.
- Industrial Applications: In manufacturing and processing, knowing the exact mass of a desired element in a raw material like FeCl₃ is vital for cost estimation, yield prediction, and quality control.
For example, if you were performing a reaction that required 100 grams of pure iron, and FeCl₃ was your source, you could use the proportion (55.845 g Fe / 162.2 g FeCl₃) to calculate the necessary mass of FeCl₃.
