Question 1: Define the principle of conservation of mass in chemical reactions.

Answer: The principle that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.

Question 2: Explain why it is important to consider closed systems when studying conservation of mass.

Answer: Because in a closed system, no mass can enter or escape, allowing accurate observation of mass changes during reactions.

Question 3: Describe a common misconception related to mass changes observed in chemical reactions.

Answer: Some students believe mass decreases or increases during reactions, but in reality, mass remains constant if all products and reactants are accounted for.

Question 1: Calculate the expected mass of water produced when 5.0 g of hydrogen reacts completely with excess oxygen. (Molar mass of H₂ = 2.02 g/mol, H₂O = 18.02 g/mol).

Answer: Mass of water = (Mass of hydrogen / molar mass of H₂) × molar mass of H₂O = (5.0 / 2.02) × 18.02 ≈ 44.7 g

Question 2: A sealed reaction vessel contains 10.0 g of magnesium and 15.0 g of sulphur. After the reaction, the total mass is measured again and found to be 25.0 g. Explain why the mass remains constant or differs, based on the conservation of mass.

Answer: The total mass remains constant because in a sealed container, no mass escapes, confirming the principle of conservation of mass during the reaction.

Question 3: Data shows that when 3.0 g of calcium carbonate decomposes, 1.2 g of calcium oxide and 1.8 g of carbon dioxide are produced. What does this data indicate about the conservation of mass?

Answer: Mass is conserved as total mass before and after equals

Question 1: Design a simple experiment to demonstrate the conservation of mass during a combustion reaction. Include the key variables and safety precautions (theory only).

Answer: Use a crucible with a lid to burn a known mass of a metal or organic material in a sealed environment to prevent gas escape. Variables include the initial mass and temperature. Safety precautions involve wearing safety goggles, handling hot equipment carefully, and working in a well-ventilated area.

Question 2: Identify two main variables that could affect the accuracy of mass measurements in such experiments and how to control them.

Answer: Variables include gas leakage and temperature fluctuations; these can be controlled by sealing the apparatus properly and conducting experiments at constant temperature.

Question 1: In industrial manufacturing, why is it important to account for all reactants and products when considering mass balance?

Answer: To ensure safety, efficiency, and compliance with laws, as well as accurate calculation of yields and waste management.

Question 2: How does the principle of conservation of mass relate to the development of sustainable chemical processes?

Answer: It ensures that all materials are accounted for, promoting waste minimisation and recycling, which are essential for sustainability. It also helps in designing processes that do not produce unaccounted emissions or residues.