Problem 75 - Chemistry The Molecular Nature of Matter

Question

It was found that \(2.35 \mathrm{~g}\) of a compound of phosphorus and chlorine contained \(0.539 \mathrm{~g}\) of phosphorus. What are the percentages by mass of phosphorus and chlorine in this compound?

Step-by-Step Solution

Answer

Phosphorus makes up 22.93% while chlorine makes up 77.07% of the compound by mass.

Step 1: Calculate the Mass of Chlorine

Subtract the mass of phosphorus from the total mass of the compound to find the mass of chlorine. Mass of chlorine = Total mass - Mass of phosphorus.

Step 2: Calculate the Percentage by Mass of Phosphorus

Divide the mass of phosphorus by the total mass of the compound and then multiply by 100 to find the percentage. Percentage of phosphorus = (Mass of phosphorus / Total mass) * 100.

Step 3: Calculate the Percentage by Mass of Chlorine

Divide the mass of chlorine by the total mass of the compound and then multiply by 100 to find the percentage. Percentage of chlorine = (Mass of chlorine / Total mass) * 100.

Key Concepts

Stoichiometry

Stoichiometry is the field of chemistry that relates to measuring the quantities of reactants and products involved in chemical reactions. In practical terms, stoichiometry helps us understand the relationships between different chemicals in a reaction, allowing for the precise calculation of the amounts of substances needed or produced.

For example, when calculating the percentage composition by mass of a compound, stoichiometry is used to determine the mass ratios of the individual elements within the compound. Here, it becomes essential for predicting how much of each element is present when given the total mass of a compound. It’s the foundation for preparing chemical solutions, synthesizing chemical compounds, and various applications in both laboratory settings and industrial processes.

Molecular Composition

The molecular composition of a chemical compound provides vital information about the types and quantities of atoms that constitute a molecule. It is crucial for understanding the physical and chemical properties such as reactivity, polarity, and phase at certain temperatures.

To elaborate, when analyzing a compound's percentage composition by mass, the molecular composition reveals the proportion of each element's mass to the entire mass of the molecule. When we dissect the phosphorus and chlorine compound from the exercise, our focus lies on establishing the molecular composition, which in turn helps us comprehend the roles that phosphorus and chlorine play, and their respective mass contribution to the compound.

Chemical Compounds

Chemical compounds are substances formed when two or more elements combine in fixed ratios, held together by chemical bonds. There are countless chemical compounds, and each one has unique properties determined by the elements that compose it and how those elements are bonded.

The percentage by mass of each element within a compound, as seen in the exercise question, is a fundamental property of compounds. It influences everything from how the compound interacts with other substances to its density and boiling/melting points. Identifying the percentage by mass is also a stepping stone to understanding more complex chemical properties and how a compound will react under specific conditions.

Quantitative Analysis

Quantitative analysis in chemistry refers to the determination of the absolute or relative abundance (often expressed as a percentage) of one, several, or all particular substance(s) present in a sample. This practice is integral to a variety of fields, including pharmacology, environmental monitoring, and material science.

The problem discussed exemplifies a simple quantitative analysis task—calculating the percentage by mass of elements in a compound. This information is indispensable as it allows scientists to ascertain the purity of a compound, verify if a sample meets the required composition for industrial applications, or aid in the identification of an unknown substance through comparison with known standards.