Question 1: Define the principle of conservation of mass in chemistry.

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

Question 2: Explain why, in a closed system, the total mass remains constant during a chemical reaction.

Answer: Because no mass is lost or gained from outside the system, so the total mass before and after the reaction stays the same.

Question 1: Calculate the number of moles in 24 grams of water (H₂O). (Molar mass of H₂O = 18 g/mol)

Answer: 1.33 mol

Question 2: A reaction involves 10 grams of magnesium reacting with excess hydrochloric acid. How many moles of magnesium are involved?

Answer: 0.41 mol

Question 3: If 5 grams of sulphur reacts completely with oxygen, how many moles of sulphur are used? (Molar mass of sulphur = 32 g/mol)

Answer: 0.156 mol

Question 1: Describe the key safety precautions that should be taken when measuring chemicals in a laboratory.

Answer: Wear safety goggles and gloves, handle chemicals carefully to avoid spills, work in a well-ventilated area, and follow proper disposal procedures.

Question 2: Explain why it is important to use a sealed container when measuring the mass of a chemical reaction in progress.

Answer: To prevent loss of reactants or products by evaporation or spillage, ensuring accurate mass measurements.

Question 1: A closed system experiment shows that the total mass before a reaction was 50.0 grams and after the reaction, the mass was 50.0 grams. What does this indicate about the reaction?

Answer: It confirms that mass is conserved during the reaction, supporting the principle of conservation of mass.

Question 2: In an open system, a gas is produced during a reaction. How might this affect the observed mass change, and why?

Answer: Mass may appear to decrease because some gas escapes into the surroundings, violating the conservation of mass in the system.

Question 1: Explain how the principle of conservation of mass is applied in chemical manufacturing industries, such as in the production of pharmaceuticals.

Answer: In pharmaceutical manufacturing, the principle ensures that the total mass of reactants used equals the mass of products and waste. This allows for precise control of reaction conditions, minimises waste, and ensures product quality and safety. It also aids in calculations for scaling up production and environmental regulations compliance.

Question 2: A chemical reaction involves 15 grams of aluminium reacting with sulfur to produce aluminium sulphide. If the molar masses are: Al = 27 g/mol, S = 32 g/mol, and Al₂S₃ = 150 g/mol, calculate the theoretical mass of aluminium sulphide produced.

Answer: Answer: 33.33 g