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One of the most fundamental principles in chemistry, established by Antoine L. Lavoisier, is the Law of Conservation of Mass. This law provides a crucial insight into what happens to mass during a chemical reaction: mass can neither be created nor destroyed in a chemical reaction. In essence, it means that in any closed system, the total mass of the reactants before a chemical reaction must be equal to the total mass of the products after the reaction.

This concept might seem intuitive now, but it was a revolutionary idea that formed the foundation of chemical sciences. Prior to this, it was not always clear whether substances gained or lost mass during transformations like burning or rusting. Lavoisier, through meticulous experiments, demonstrated that mass is conserved.

Let's imagine an experiment that illustrates this law (Activity 3.1):

You would take two chemical solutions, say copper sulphate (Solution X) and sodium carbonate (Solution Y). You'd prepare 5% solutions of each. Then, you'd carefully place a small ignition tube containing Solution X inside a conical flask that holds Solution Y, ensuring the solutions do not mix initially. After sealing the flask with a cork, you would weigh the entire setup carefully.

Next, you would tilt and swirl the flask, allowing Solution X and Solution Y to mix and react. A chemical reaction would occur, potentially forming new substances. After the reaction is complete, you would weigh the flask with its new contents again.

What would you observe? Despite the chemical reaction taking place and new substances being formed, the mass of the flask and its contents would remain unchanged. This consistency in total mass before and after the reaction confirms the Law of Conservation of Mass. The cork is essential here to ensure that no gases escape or enter the flask, maintaining a closed system for accurate mass measurement.This law is a cornerstone of quantitative chemistry. It allows chemists to predict the mass of products formed from a given mass of reactants, or vice versa, making it indispensable for chemical calculations and industrial processes. It highlights that matter is simply rearranged during chemical transformations, not created or annihilated.

Fun Fact: Lavoisier's rigorous use of the balance in his experiments was key to establishing the Law of Conservation of Mass, shifting chemistry towards a more quantitative science.

Question for You: In a reaction, 5.3 g of sodium carbonate reacts with 6 g of acetic acid. The products are 2.2 g of carbon dioxide, 0.9 g of water, and 8.2 g of sodium acetate. Show how these observations are in agreement with the law of conservation of mass.