Question

The early alchemists used to do an experiment in which water was boiled for several days in a sealed glass container. Eventually, some solid residue would appear in the bottom of the flask, which was interpreted to mean that some of the water in the flask had been converted into "earth." When Lavoisier repeated this experiment, he found that the water weighed the same before and after heating and the mass of the flask plus the solid residue equaled the original mass of the flask. Were the alchemists correct? Explain what happened. (This experiment is described in the article by A. F. Scott in Scientific American, January \(1984 .\)

Short answer

The alchemists were incorrect in their interpretation that some water was converted into "earth" during the experiment. Lavoisier's results, along with the principle of conservation of mass, showed that the mass of water remained the same before and after heating, and the total mass of the system did not change. The solid residue that appeared at the bottom of the flask was likely a result of impurities or minerals present in the water that collected and solidified during the boiling process, rather than a conversion of water into "earth."

Step-by-step solution

Understanding the experiment results

We know that the early alchemists observed a solid residue appearing in the bottom of the flask after boiling water in a sealed glass container. They inferred that some water was converted into "earth." However, when Lavoisier repeated the experiment, he noticed that the mass of the water remained the same before and after heating. Moreover, the combined mass of the flask and the solid residue was equal to the original mass of the flask.

Conservation of mass

The principle of conservation of matter states that the total mass of a system remains constant during any chemical reaction. Here, the total mass of the flask and the solid residue equaled the original mass of the flask, meaning that no new mass was created. This supports the notion that no water was converted into "earth."

Analyzing the solid residue

Since the mass of the water did not change and the conservation of mass principle suggests that no additional mass was created, the solid residue observed by the early alchemists must have been present from the beginning. It is likely that this residue was either impurities in the water or minerals dissolved in it. When the water was boiled, these impurities or minerals may have collected and solidified at the bottom of the flask.

Conclusion

The alchemists were not correct in their interpretation that some water was converted to "earth." The results of Lavoisier's experiment, along with the principle of conservation of mass, suggest that the solid residue observed at the end of the experiment was not a conversion of water but rather a concentration of impurities or minerals that were already present in the initial sample of water.

Key concepts

Law of Conservation of Matter

The Law of Conservation of Matter is a fundamental principle in chemistry that posits matter cannot be created or destroyed in an isolated system. This means that during any chemical reaction, the mass of the reactants (substances before the reaction) must equal the mass of the products (substances after the reaction).

Considering the alchemists' experiment, they thought the appearance of a solid residue implied a transformation of water into 'earth'. In reality, the law tells us this cannot happen; the matter is simply changing form, not disappearing or appearing from nowhere.

Principle of Conservation of Mass

The Principle of Conservation of Mass is closely related to the Law of Conservation of Matter, with the emphasis on mass being the measurable quantity. This principle was key to disproving the alchemists' error. When Lavoisier repeated the water-boiling experiment, he carefully measured the masses and validated this principle: the collective mass of the sealed flask, water, and any residue was conserved. No mass had vanished or been created; it merely changed in its physical presence, highlighting the importance of precise measurement in chemical investigations.

Alchemy and Early Chemistry

Alchemy, the precursor to modern chemistry, was a medley of philosophy, mysticism, and early scientific attempts to understand nature. Alchemists sought to transform base materials into noble ones, like lead into gold. However, their understanding of matter was not grounded in empirical evidence. It was Lavoisier's methodical experiments and measurements that began to transform alchemy into the more empirical science of chemistry, shifting the focus from mystical interpretations to reproducible observations.

Chemical Reactions and Mass

Every chemical reaction involves rearrangements of atoms and molecules, but it's crucial to understand that these rearrangements conserve mass. Whether a solid precipitate forms from a solution, a gas evolves from a liquid, or a complex compound breaks down into simpler substances, the total mass remains unchanged. The alchemists' experiment, where boiling water produced a solid residue, perfectly illustrates this concept. The solid didn't come from water itself but from impurities or dissolved minerals that were already part of the system's total mass.

Lavoisier's Experiments

Antoine-Laurent de Lavoisier, often referred to as the 'father of modern chemistry', conducted meticulous experiments that laid the groundwork for the law of conservation of mass. He applied rigorous scientific methods and precise measurements that were uncommon at the time. His replication of the alchemists' water-boiling experiment clearly demonstrated that matter doesn't appear or disappear; it merely changes forms. Lavoisier's work is a cornerstone in chemistry, reminding us that proper scientific methodology and accurate measurements are essential for gaining a true understanding of natural phenomena.