This question is about olive oil - AQA - A-Level Chemistry - Question 9 - 2022 - Paper 2

Using the volume and concentration of Br₂:

The formula to calculate moles is: $ext{moles} = ext{concentration} imes ext{volume}$

Here, the concentration is 0.025 mol/dm³ and the volume is 0.030 dm³ (30.0 cm³): $ext{moles} = 0.025 imes 0.030 = 7.5 imes 10^{-4} ext{ mol}$

To find the mass of olive oil, first calculate the moles of Y:

From Question 09.1, we have 7.5 × 10⁻⁴ mol of Br₂, which reacts with Y:

yield Y = 7.5 × 10^{-4} ext{ mol}

Molar mass of Y = 880 g/mol:

Mass of Y = moles × molar mass: $ext{Mass of Y} = 7.5 imes 10^{-4} ext{ mol} imes 880 ext{ g/mol} = 0.66 ext{ g}$

Since the olive oil contains 85% Y by mass:

Let the total mass of olive oil be m: $0.85m = 0.66 ext{ g}$

Thus, m = \frac{0.66 ext{ g}}{0.85} = 0.776 ext{ g} ext{ (approximately)}

Extra step: Rinse the bottle with solvent after transfer and record the mass.

Justification: This ensures that all the olive oil is transferred to the volumetric flask without leaving residues, which would affect the accuracy of the measured mass.

To ensure that the solution is homogeneous. This is important for uniform distribution of the olive oil within the solvent, which guarantees consistency in the solution for accurate titration.

From the mass spectrum, the ion with m/z = 345 corresponds to the compound. The empirical formula is given as CxHyOz.

To determine the molar mass: Molar mass of C = 12 g/mol, H = 1 g/mol, O = 16 g/mol.

Assuming x = 6, y = 12, z = 1 yields: $6 imes 12 + 12 imes 1 + 1 imes 16 = 72 + 12 + 16 = 100 ext{ g/mol}$ This shows the empirical formula must have a higher ratio to match 345 g/mol, leading to an increased formula of C18H36O, thus deducing the molecular formula as C18H36O.