Problem 22 - Chemistry Matter and Change

Question

Two unknown compounds are tested. Compound I contains 15.0 \(\mathrm{g}\) of hydrogen and 120.0 g of oxygen. Compound II contains 2.0 \(\mathrm{g}\) of hydrogen and 32.0 \(\mathrm{g}\) of oxygen. Are the compounds the same? Explain your answer.

Step-by-Step Solution

Answer

The compounds are not the same; their mass ratios differ.

Step 1: Calculate the Mass Ratio for Compound I

For Compound I, divide the mass of hydrogen by the mass of oxygen to find the mass ratio. \[ \text{Mass Ratio for Compound I} = \frac{15.0 \text{ g of hydrogen}}{120.0 \text{ g of oxygen}} = \frac{1}{8} \]

Step 2: Calculate the Mass Ratio for Compound II

For Compound II, divide the mass of hydrogen by the mass of oxygen to find the mass ratio.\[ \text{Mass Ratio for Compound II} = \frac{2.0 \text{ g of hydrogen}}{32.0 \text{ g of oxygen}} = \frac{1}{16} \]

Step 3: Compare the Mass Ratios

Compare the mass ratios obtained for Compound I and Compound II. - Compound I has a mass ratio of \( \frac{1}{8} \).- Compound II has a mass ratio of \( \frac{1}{16} \).Since the mass ratios are different, the compounds are not the same.

Key Concepts

Chemical Compounds

Chemical compounds are substances that are composed of two or more different chemical elements that are chemically bonded together. The bonds can be covalent, ionic, or metallic, depending on the elements involved and the nature of their interaction. A compound has a fixed ratio of its constituent elements, which determines its chemical properties and makes it distinct from other substances. Each compound has specific properties that are independent of the amounts of the constituents, and these properties help classify and identify the compound in chemical analysis.

For example, water (H2O) is a chemical compound consisting of hydrogen and oxygen bonded in a 2:1 ratio by mass. This ratio is consistent, meaning water will always have two hydrogen atoms for every one oxygen atom. Understanding the composition and structure of compounds is fundamental to the study of chemistry, helping chemists predict reactions and design new materials.

Mass Ratio

The mass ratio in compounds refers to the proportion of the mass of one element to another within the compound. It is crucial in determining whether two substances are the same compound. By comparing mass ratios, chemists can identify substances and establish if they conform to the Law of Definite Proportions. This law states that a chemical compound always contains exactly the same proportion of elements by mass, no matter the size of the sample.

In the given exercise, Compound I and Compound II are analyzed for their mass ratios:

• Compound I: Mass Ratio = \( \frac{1}{8} \), with hydrogen to oxygen.
• Compound II: Mass Ratio = \( \frac{1}{16} \), with hydrogen to oxygen.

By comparing these ratios, we can determine that the compounds are not the same since their mass ratios differ. Compound I has a more significant proportion of hydrogen compared to Compound II, indicating different compositions.

Chemical Analysis

Chemical analysis is the process of identifying the components and composition of substances. This involves various techniques and methods to analyze chemical compounds and determine their characteristics, including elemental composition. One of the basic methodologies of analysis is by calculating mass ratios, which can provide information on the identity of the compound and its purity.

In the exercise, the chemical analysis is performed by calculating and comparing the mass ratios of hydrogen to oxygen in the two compounds. Through this analysis:

• Compound I has a \( 1:8 \) mass ratio.
• Compound II has a \( 1:16 \) mass ratio.

This crucial analysis reveals that since the ratios differ, these compounds are not identical. Thus, chemical analysis helps distinguish between different compounds, supporting fundamental concepts such as the Law of Definite Proportions by confirming or disproving the sameness of two chemical substances based on their mass ratios.