Question 1: What is the Relative Formula Mass (Mr) of a compound?

Answer: The relative formula mass (Mr) of a compound is the sum of the atomic masses of all atoms in its formula, relative to 1/12 the mass of a carbon-12 atom.

Question 2: Explain why Relative Formula Mass is useful in chemistry.

Answer: It allows chemists to calculate the amounts of substances involved in reactions accurately by relating molecular or formula weights to a standard atomic mass.

Question 1: Calculate the Mr of water (H₂O). Atomic masses: H = 1, O = 16.

Answer: Mr = (2 × 1) + 16 = 18

Question 2: Determine the Mr of sulphuric acid (H₂SO₄). Atomic masses: H = 1, S = 32, O = 16.

Answer: Mr = (2 × 1) + 32 + (4 × 16) = 98

Question 3: A compound contains 2 atoms of aluminium and 3 atoms of sulphur. Atomic masses: Al = 27, S = 32. Calculate its Mr.

Answer: Mr = (2 × 27) + (3 × 32) = 54 + 96 = 150

Question 1: Describe a simple experiment to determine the Mr of a salt such as sodium chloride (NaCl). Include safety precautions.

Answer: You can weigh a known mass of NaCl and dissolve it in water to make a solution. Then, evaporate the water to recover the salt and weigh it again. The Mr can be estimated by comparing the mass of the recovered salt to the amount dissolved, considering the initial amount used. Safety precautions include wearing goggles, gloves, and working in a well-ventilated area to avoid inhalation or contact with chemicals.

Question 2: Identify two variables that could affect the accuracy of measuring the Mr in a practical experiment.

Answer: Purity of the salt and precision of the weighing scales.

Question 1: In the pharmaceutical industry, why is calculating the Mr of compounds important?

Answer: It ensures correct dosages, quality control, and consistency in drug production.

Question 2: A new material contains 60% by mass of element X with atomic mass 50, and 40% of element Y with atomic mass 20. Calculate the approximate Mr of the compound assuming a 1:1 ratio.

Answer: Mr ≈ (0.6 × 50) + (0.4 × 20) = 30 + 8 = 38 (for a 1:1 ratio, the approximate Mr is 38)