Determining the Empirical Formula of a Hydrated Salt: A Detailed Guide

Welcome to our comprehensive guide on determining the empirical formula of a hydrated salt. In this article, we will walk you through the detailed steps to find the empirical formula of a hydrated salt T, which consists of 20.2% iron (Fe), 11.5% sulfur (S), 23% oxygen (O), and water of crystallization. We will break down the process into several steps, demonstrating how to calculate the empirical formula and how to consider the water of crystallization.

Understanding the Composition of Salt T

The salt T is composed of various elements, including iron, sulfur, oxygen, and water of crystallization. The percentages for iron, sulfur, and oxygen add up to 54.7%, indicating that the remaining 45.3% is due to water of crystallization. Understanding this composition is the first step in determining the empirical formula.

Step 1: Determine the Mass of Each Element in 100 g of the Compound

To start, we need to find the mass of each element in 100 grams of the compound.

Iron (Fe): 20.2 g Sulfur (S): 11.5 g Oxygen (O): 23 g

Step 2: Calculate the Moles of Each Element

Using the molar masses of each element, we can calculate the moles of each element.

Iron (Fe)

Moles of Fe 20.2 g / 55.85 g/mol 0.362 mol

Sulfur (S)

Moles of S 11.5 g / 32.07 g/mol 0.359 mol

Oxygen (O)

Moles of O 23 g / 16.00 g/mol 1.438 mol

Step 3: Determine the Mole Ratio

Now, we need to determine the mole ratio by dividing each mole value by the smallest number of moles calculated.

For Iron (Fe)

Mole ratio of Fe 0.362 / 0.359 ≈ 1

For Sulfur (S)

Mole ratio of S 0.359 / 0.359 ≈ 1

For Oxygen (O)

Mole ratio of O 1.438 / 0.359 ≈ 4

Step 4: Write the Empirical Formula

The ratio of moles is approximately:

Iron (Fe): 1 Sulfur (S): 1 Oxygen (O): 4

Thus, the empirical formula for the anhydrous part of the salt is FeS4.

Step 5: Consider the Water of Crystallization

To find the water of crystallization, we need to calculate the mass percentage of water. The total percentage of Fe, S, and O is 54.7%, so the percentage of water is:

100 - 54.7 45.3%

The mass of water (H2O) can be calculated as:

45.3 g / 18 g/mol 2.5 moles

So, the empirical formula for the hydrated salt can be expressed as FeS4·nH2O, where n is the number of moles of water of crystallization. In this case, it would be:

FeS4·2.5/0.36 H2O or FeS4·7H2O

Conclusion

In summary, the empirical formula of the hydrated salt T can be expressed as FeS4·nH2O. For the anhydrous part, the empirical formula is FeS4, and based on the water of crystallization, the formula can be written as FeS4·7H2O.