Question

. A 4.78-g sample of aluminum completely reacts with oxygen to form 6.67 g of aluminum oxide. Use this data to calculate the mass percent composition of aluminum in aluminum oxide.

Short answer

The mass percent composition of aluminum in aluminum oxide is approximately 71.51%.

Step-by-step solution

Calculate the mass of oxygen in the compound

Subtract the mass of aluminum from the mass of the aluminum oxide to find the mass of oxygen. This is done by the equation: mass of oxygen = mass of aluminum oxide - mass of aluminum.

Calculate the mass percent composition of aluminum

Divide the mass of aluminum by the total mass of aluminum oxide and multiply by 100% to determine the mass percent composition of aluminum in aluminum oxide. Use the formula: mass percent of Al = (mass of Al / mass of Al2O3) * 100%.

Key concepts

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. This concept is central to calculating the amounts of substances needed or produced in a reaction.

Think of stoichiometry as a tool for cooking: just as you need the right amount of each ingredient to bake a cake, you need the correct amounts of reactants to carry out a reaction efficiently. In the given exercise, stoichiometry is used to figure out how much aluminum and oxygen are needed to produce aluminum oxide.

When practicing stoichiometry, it's important to:

• Balance the chemical equation for the reaction.
• Convert masses to moles using molar mass as a conversion factor.
• Use the balanced equation to set up mole ratios.
• Convert moles back to mass if required.

Applying stoichiometry helps in understanding how different quantities of reactants are used up and products are formed, which leads to calculating mass percent composition.

Aluminum Oxide Reaction

The reaction between aluminum and oxygen to form aluminum oxide is an example of a synthesis reaction, where two or more elements or simple compounds combine to form a more complex one.

Represented by the equation \(4Al + 3O_2 \rightarrow 2Al_2O_3\), the reaction involves the transformation of elemental aluminum and oxygen into aluminum oxide. Understanding this reaction is crucial because it showcases the law of conservation of mass, where the mass of reactants equals the mass of products.

For students learning about this process, it's essential to notice that aluminum is a highly reactive metal, and when exposed to air, it tends to form a layer of aluminum oxide on its surface, preventing further oxidation. This property makes aluminum resistant to corrosion in everyday use.

Chemical Composition Calculation

Chemical composition calculation involves determining the relative amounts of elements in a chemical compound. For students, it's like solving a mystery: figuring out what's inside a compound and in what proportion.

The mass percent composition of an element in a compound gives the ratio of the mass of that element to the total mass of the compound, expressed as a percentage. Calculating it involves:

• Finding the mass of each element in the compound.
• Calculating the total mass of the compound.
• Determining the percentage of each element's mass relative to the total mass.

In the exercise, the mass percent composition (\(mass\%\)) of aluminum (Al) in aluminum oxide (Al₂O₃) is calculated using the formula \(mass\% of Al = \frac{mass of Al}{mass of Al_2O_3} \times 100\%\). This concept not only helps in understanding the makeup of compounds but is also foundational in material sciences, where composition critically affects the properties of materials.