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

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

Question 2: Explain why the mass of reactants and products remains the same in a sealed reaction vessel.

Answer: Because no mass is lost or gained; the reaction occurs in a closed system, ensuring the total mass stays constant.

Question 1: Calculate the mass of 2 moles of sulphur (S₈). (Atomic mass of S ≈ 32 g/mol)

Answer: Mass = 2 mol × 256 g/mol = 512 g

Question 2: A reaction involves 5 grams of magnesium reacting with excess hydrochloric acid. Write the balanced equation and determine the moles of magnesium used.

Answer: Mg + 2HCl → MgCl₂ + H₂; Molar mass of Mg = 24 g/mol; Moles = 5 g ÷ 24 g/mol ≈ 0.208 mol

Question 1: Describe an experiment to demonstrate the conservation of mass during a chemical reaction. Include variables to control and safety precautions.

Answer: An experiment can involve sealing reactants in a reaction vessel and measuring the mass before and after the reaction. Variables to control include temperature, pressure, and ensuring the vessel remains airtight. Safety precautions include wearing safety goggles, gloves, and handling chemicals with care to prevent spills or reactions that could be hazardous.

Question 2: Identify the independent, dependent, and control variables in an experiment measuring the mass change when magnesium reacts with hydrochloric acid.

Answer: Independent variable: Amount of hydrochloric acid; Dependent variable: Mass change; Control variables: Temperature, pressure, amount of magnesium

Question 1: A student measures the mass of reactants as 10.00 g and the mass of products as 9.95 g in an open system. Explain why the masses differ and how this relates to the principle of conservation of mass.

Answer: The mass difference is due to gases or vapours escaping into the surroundings, which is why the total mass appears to decrease. In a closed system, the total mass would remain the same, demonstrating the conservation of mass.

Question 1: Explain how the conservation of mass is important in chemical manufacturing processes, such as in the production of pharmaceuticals.

Answer: In pharmaceutical manufacturing, ensuring the conservation of mass is crucial for accurate formulation, quality control, and safety. It ensures all reactants are fully accounted for, prevents loss of valuable chemicals, and helps in predicting yields and waste management.