Question

Sulfur dioxide is a gas formed as a by-product of burning coal. Sulfur trioxide is a significant contributor to acid rain. Does the existence of these two substances violate the law of multiple proportions? Explain.

Short answer

No, the existence of sulfur dioxide (SO2) and sulfur trioxide (SO3) does not violate the law of multiple proportions as the ratios between the amounts of oxygen that combine with a fixed amount of sulfur are simple whole numbers.

Step-by-step solution

Understanding the Law of Multiple Proportions

The law of multiple proportions states that when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Analyzing the Composition of Sulfur Dioxide (SO2)

For sulfur dioxide (SO2), one sulfur atom is combined with two oxygen atoms. If we assume a fixed mass of sulfur, the ratio of the oxygen mass to the sulfur mass can be calculated based on their atomic weights.

Analyzing the Composition of Sulfur Trioxide (SO3)

For sulfur trioxide (SO3), one sulfur atom is combined with three oxygen atoms. We compare the mass ratio of oxygen to sulfur in SO3 with the ratio in SO2.

Comparing the Ratios

The ratio of oxygen to sulfur in SO2 and SO3 should be simple whole numbers if they comply with the law of multiple proportions. This can be illustrated by taking the atomic mass of sulfur as a constant and comparing the resulting ratios of oxygen in the two compounds

Conclusion

Since SO2 and SO3 are both oxides of sulfur and the ratios of oxygen to sulfur in both compounds are simple whole numbers, the existence of these two substances does not violate the law of multiple proportions.

Key concepts

Chemical Composition

The term chemical composition refers to the arrangement, type, and ratio of atoms in molecules of chemical substances. The chemical composition determines the fundamental properties of a substance and dictates how it will react with other substances. Understanding the chemical composition is essential when exploring the concepts of chemical compounds and the laws that govern their formation, such as the law of multiple proportions.

Take sulfur dioxide (SO2) and sulfur trioxide (SO3), for instance. Sulfur dioxide consists of one sulfur atom and two oxygen atoms, while sulfur trioxide comprises one sulfur atom and three oxygen atoms. Their differing compositions are an example of how a common element (sulfur) can combine in different proportions with another element (oxygen) to form distinct substances with unique properties, such as their role in the creation of acid rain.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It is built on the conservation of mass and the concept of mole ratios, where the coefficients in a balanced chemical equation indicate the proportions of each substance involved. Through stoichiometry, chemists can predict the amounts of substances consumed and produced in a reaction.

The stoichiometric analysis is what enables us to compare the ratios of the elements in SO2 and SO3. By determining these ratios, we can apply the law of multiple proportions to evaluate the existence of these two distinct chemical compounds. Stoichiometry is what bridges these comparisons and enforces a quantitative understanding of the differences in chemical compositions.

Molar Mass Calculation

The molar mass of a substance is the mass in grams of one mole of its particles (atoms, molecules, ions, etc.). It is a fundamental concept in stoichiometry for converting between moles and grams. To calculate molar mass, we use the atomic weights of the elements from the periodic table and multiply them by the number of each type of atom in the molecule.

For instance, knowing the molar mass of both sulfur and oxygen allows us to find the mass ratios of oxygen to sulfur in SO2 and SO3. By doing so, we affirm that these mass ratios are small whole numbers, aligning with the requirements of the law of multiple proportions. This validates that the existence of both sulfur dioxide and sulfur trioxide does not contravene this law, but rather exemplifies it.

Chemical Compounds

A chemical compound is a substance formed when two or more elements are chemically bonded together. The properties of a compound are different from those of its constituent elements. Sulfur dioxide and sulfur trioxide are typical examples of chemical compounds, where sulfur bonds with oxygen in different proportions.

In the context of the law of multiple proportions, when we identify these unique, pure substances, we look at their composition to verify that it adheres to this principle. The law's embodiment in the existence of SO2 and SO3 demonstrates that these two different compounds, with unique properties and chemical behavior, are in direct correlation with their simple and distinct elemental ratios. Consequently, studying chemical compounds like these aids in the broader comprehension of chemical reactions and the laws that govern the formation of various substances.