Determining the Empirical Formula of a Hydrocarbon from Combustion Analysis

Understanding the empirical formula of a hydrocarbon from its combustion analysis is a fundamental concept in chemistry. This article will guide you through the step-by-step process of calculating the empirical formula of a hydrocarbon that burns to produce a specific amount of water. We will use the example provided, where 5.8g of a hydrocarbon produces 9g of water as a result of combustion.

Step-by-Step Calculation

Let's break down the process into clear steps, starting with the fundamental principles and calculations.

Step 1: Calculate Moles of Water

First, we need to find the moles of water produced. The molar mass of water (H2O) is approximately 18g/mol.

Moles of H2O mass / molar mass 9g / 18g/mol 0.5 mol

Step 2: Calculate Moles of Hydrogen

Each mole of water contains 2 moles of hydrogen atoms. Therefore, the moles of hydrogen are:

Moles of H 0.5 mol × 2 1 mol

Step 3: Calculate Mass of Hydrogen

Now, using the molar mass of hydrogen (1g/mol), we can find the mass of hydrogen:

Mass of H moles × molar mass 1 mol × 1g/mol 1 g

Step 4: Calculate Mass of Carbon

We know the initial mass of the hydrocarbon is 5.8g. Subtracting the mass of hydrogen from the total mass gives us the mass of carbon:

Mass of C mass of hydrocarbon - mass of H 5.8g - 1g 4.8g

Step 5: Calculate Moles of Carbon

The molar mass of carbon (C) is approximately 12 g/mol. We can now calculate the moles of carbon:

Moles of C mass / molar mass 4.8g / 12g/mol 0.4 mol

Step 6: Determine the Simplest Mole Ratio

We now have the moles of carbon and hydrogen:

Moles of C 0.4 mol

Moles of H 1 mol

To find the simplest mole ratio, we divide both by the smallest number of moles:

Carbon ratio (C) moles of C / smallest number of moles 0.4 / 0.4 1

Hydrogen ratio (H) moles of H / smallest number of moles 1 / 0.4 2.5

Since we cannot have a fraction in the empirical formula, we multiply both ratios by 2 to get whole numbers:

Final C ratio 1 × 2 2

Final H ratio 2.5 × 2 5

Conclusion

The empirical formula of the hydrocarbon is C2H5. This indicates that the simplest ratio of carbon to hydrogen in the hydrocarbon is 2:5.

Advanced Explanation

Well, to start, we determine the molar quantities of the combustion products carbon dioxide (CO2) and water (H2O). Let's consider an example similar to the one provided:

Molar quantity of carbon dioxide: n_{CO_{2}g} frac{12.6g}{44.01g cdot mol^{-1}} 0.286 mol

Molar quantity of water: n_{H_{2}Ol} frac{5.13g}{18.01g cdot mol^{-1}} 0.285 mol

There were thus 0.570 mol with respect to hydrogen in the initial sample. The reason we double the molar quantity of water is to account for the two hydrogen atoms per molecule of water, which is a standard practice in such calculations.

In this advanced explanation, we emphasize the importance of understanding the stoichiometry and molar relationships in combustion reactions. By calculating the molar quantities of both CO2 and H2O, we can correctly determine the empirical formula of the hydrocarbon. This method is crucial for analyzing the composition of unknown hydrocarbons and can be applied to various types of combustion analysis problems.

If you are interested in further exploring the principles of hydrocarbon analysis and empirical formula determination, there are numerous online resources and textbooks available. Additionally, practical experiments and laboratory exercises can greatly enhance your understanding of these concepts.

Keywords

To assist with search optimization, we recommend focusing on the following keywords:

hydrocarbon combustion

empirical formula

stoichiometry

hydrogen and carbon ratios