Mercury(II) oxide, a red powder, can be decomposed by heating to produce liquid mercury and oxygen gas. When a sample of this compound is decomposed, \(3.87 \mathrm{~g}\) of oxygen and \(48.43 \mathrm{~g}\) of mercury are produced. \(\operatorname{In}\) a second experiment, \(15.68 \mathrm{~g}\) of mercury is allowed to react with an excess of oxygen and \(16.93 \mathrm{~g}\) of red mercury(II) oxide is produced. Show that these results are consistent with the law of constant composition.

Chemical reactions involve the transformation of substances through the breaking and forming of chemical bonds. They are governed by certain principles and laws that dictate how substances combine or decompose. The decomposition of mercury(II) oxide into liquid mercury and oxygen gas is a chemical reaction where heat acts as the catalyst for breaking the chemical bonds. In a classroom or laboratory setting, students typically explore this concept by observing changes in color, state of matter, and mass, as well as by measuring the amounts of substances before and after a reaction. This hands-on experience helps students understand how different elements react under certain conditions and the fundamentals of how reactions proceed.

During chemical reactions, the total mass of the system remains constant, adhering to the principle of mass conservation. This principle is crucial in understanding that matter is neither created nor destroyed, only transformed. Students are encouraged to meticulously measure and record the mass of substances in experiments to comprehend fully the mass conservation principle. Furthermore, interpreting these results leads to a broader understanding of reaction stoichiography and how to calculate mass ratios—a core concept used in advanced chemistry studies.

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It provides the framework for understanding the proportions of substances that must combine to produce a given amount of product or how much product results from certain amounts of reactants. Central to stoichiometry is the concept of the mole, which allows chemists to count particles of substances (atoms, molecules, ions) in lab-scale amounts of material.

For students, mastering stoichiometry is key because it not only helps them calculate the yield of a reaction but also assists in predicting how much of each substance is needed for a reaction to proceed completely. This is imperative in chemical manufacturing and lab experiments, where efficiency and accuracy are vital. To illustrate the application of stoichiometry, educators often present problems requiring students to balance chemical equations and use those balanced equations to conduct mass-mass or volume-volume calculations. Through practice, such exercises enable students to develop confidence in managing the numerical aspects of chemistry.

Mass ratio calculation is an essential aspect of stoichiometry and chemical reactions. It represents the proportion by mass of elements in a compound, reflecting the law of constant composition. This law asserts that a given chemical compound will always contain the same elements in the same mass ratio, regardless of the sample size or its source. It's also known as Proust's Law, named after the French chemist Joseph Proust who formulated it in the late 18th century.

In practice, when students calculate mass ratios from experimental data, they can verify the law of constant composition. As observed in the textbook's provided experiments, they measure the masses of mercury and oxygen before and after a reaction to obtain mass ratios that should, theoretically, be identical. Any differentiation between the ratios is often attributed to experimental errors—such as imprecise measurements, equipment calibration issues, or impurities in the substances used.

Students can enhance their grasp of mass ratio calculations by paying meticulous attention to measurement techniques, ensuring their calculations are correct, and understanding that their results will either confirm the fundamental principles of chemistry like the law of constant composition, or lead to questions that may require further experimentation.