Ch.4 - Chemical Quantities & Aqueous Reactions

Tro - Chemistry: A Molecular Approach 4th Edition

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Tro 4th Edition

Ch.4 - Chemical Quantities & Aqueous Reactions

Problem 108

Chapter 4, Problem 108

The combustion of liquid ethanol (C₂H₅OH) produces carbon dioxide and water. After 4.62 mL of ethanol (density = 0.789 g/mL) is allowed to burn in the presence of 15.55 g of oxygen gas, 3.72 mL of water (density = 1.00 g/mL) is collected. Determine the percent yield for the reaction. (Hint: Write a balanced equation for the combustion of ethanol.)

Verified step by step guidance

Step 1: Write the balanced chemical equation for the combustion of ethanol. The balanced equation is: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O.

Step 2: Convert the volume of ethanol to mass using its density. The formula to use is mass = volume x density. In this case, the volume of ethanol is 4.62 mL and the density is 0.789 g/mL.

Step 3: Convert the mass of ethanol to moles using its molar mass. The molar mass of ethanol is approximately 46.07 g/mol.

Step 4: Determine the theoretical yield of water. According to the balanced equation, 3 moles of water are produced for every mole of ethanol. So, multiply the moles of ethanol by 3 to get the theoretical yield of water in moles. Then, convert this to grams using the molar mass of water (18.015 g/mol).

Step 5: Convert the volume of water collected to mass using its density (1.00 g/mL), then calculate the percent yield using the formula: percent yield = (actual yield / theoretical yield) x 100%. The actual yield is the mass of water collected, and the theoretical yield was calculated in the previous step.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, producing heat and light. In the case of ethanol, the balanced equation for its combustion is C2H5OH + 3O2 → 2CO2 + 3H2O. Understanding this reaction is crucial for determining the stoichiometry involved and the theoretical yield of products.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on the balanced equation. It allows us to determine how much of each substance is consumed or produced. In this question, stoichiometry is essential for calculating the theoretical yield of water produced from the combustion of ethanol, which is then compared to the actual yield to find the percent yield.

Percent Yield

Percent yield is a measure of the efficiency of a chemical reaction, calculated by comparing the actual yield of a product to the theoretical yield. It is expressed as a percentage using the formula: (actual yield / theoretical yield) × 100%. In this scenario, calculating the percent yield of water produced from the combustion of ethanol will provide insight into the reaction's efficiency.

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