Question

A 0.45-g sample of aspirin is decomposed into its constituent elements and found to contain 0.27 g C, 0.020 g H, and 0.16 g O. Calculate the mass percent composition of C, H, and O in aspirin.

Short answer

The mass percent composition of C is 60%, H is 4.44%, and O is 35.56%.

Step-by-step solution

Establish the Total Mass of the Sample

Sum the masses of carbon (C), hydrogen (H), and oxygen (O) to find the total mass of the aspirin sample.

Calculate the Mass Percent of Carbon

Divide the mass of carbon by the total mass of the sample and multiply by 100 to get the mass percent of carbon.

Calculate the Mass Percent of Hydrogen

Similar to Step 2, divide the mass of hydrogen by the total mass of the sample and multiply by 100 to get the mass percent of hydrogen.

Calculate the Mass Percent of Oxygen

Use the same method as in Step 2 and 3 for oxygen: Divide the mass of oxygen by the total mass of the sample and multiply by 100 to get the mass percent of oxygen.

Key concepts

Percent Composition by Mass

Understanding the percent composition by mass is essential in chemistry. It provides us with the percentage by mass of each element within a compound. To clarify, consider a simple example: if you have a chocolate bar with nuts, you could say that the percent composition tells us exactly how much chocolate and nuts are present in terms of mass percentages.

For our aspirin sample, we're looking at carbon (C), hydrogen (H), and oxygen (O) – the foundational building blocks. By determining the mass percentage of these elements, we gain insight into the compound's makeup much like understanding the recipe to our chocolate bar. Here are the steps to calculate mass percent composition using our aspirin example:

• Find the total mass: Add up the individual masses of C, H, and O.
• Calculate individual percentages: Divide the mass of each element by the total mass and then multiply by 100.

By thoroughly following these steps, we end up with a clear understanding of what portion of the sample consists of each element.

Chemical Composition

The chemical composition of a substance represents which elements are present and in what proportions. Think of it as the ingredient list on a food label. Instead of fats, proteins, and carbohydrates, the 'label' of a compound like aspirin details elements like carbon, hydrogen, and oxygen. In our exercise, chemical composition is determined by breaking down aspirin and quantifying the mass of the individual elements.

Chemical composition can be especially important in pharmaceuticals, where the precise amounts of each element can impact the medication's effectiveness and safety. In a classroom or laboratory setting, exercises like these demonstrate how one can deduce the elemental makeup of a compound based purely on empirical data.

Stoichiometry

Diving deeper into chemistry, we encounter stoichiometry, which studies the quantitative relationships between reactants and products in a chemical reaction. Visualize it as a recipe where stoichiometry dictates how much of each ingredient we need to achieve our desired end product, without any leftovers or shortages.

While our original exercise does not directly deal with a chemical reaction, understanding stoichiometry is paramount when taking mass percent composition to the next level. Imagine you need to know how much aspirin can be produced from a given amount of starting materials. Stoichiometry provides the roadmap for these calculations. It ensures that our reactions are efficient, economical, and environmentally friendly, maximizing yield while minimizing waste.