Water boils when the pressure of its vapour above the liquid surface is equal to the atmospheric pressure. When substances are dissolved in water, the vapour pressure of the water is reduced and its boiling point is increased. The increase in boiling point is known as the boiling point elevation, ∆T, which is the difference between the boiling point of a solution and the boiling point of pure water. ∆T is usually small, often less than 1°C. When glucose is dissolved in 1 kg of water, the relationship between ∆T and the number of moles of glucose dissolved is as shown. ∆T = K_b × Z K_b is the boiling point constant of pure water Z = number of moles of glucose / mass of water, in kg in molkg⁻¹ A student carries out an experiment to determine the boiling point constant, K_b, for water. The student uses anhydrous glucose, C6H12O6, as the solute because it is non-volatile and very soluble in water. The experimental set-up the student uses is shown. [Figure showing digital meter, 99.48 °C, digital probe thermometer, reflux condenser, two-neck round-bottomed flask, 75.00 g distilled water, anti-bumping granules, heat] The student follows this procedure. 1 Transfer 75.00 g of distilled water to the round-bottomed flask. 2 Add anti-bumping granules to the distilled water to prevent violent, uneven boiling. 3 Heat the distilled water until it boils and record the highest stable temperature. 4 Stop heating and allow the distilled water to cool to room temperature. 5 Remove the reflux condenser and add about 1g of anhydrous glucose, measured accurately. 6 Replace the reflux condenser and heat the solution until it boils, noting the highest stable temperature. 7 Repeat steps 4 to 6, each time adding approximately 1g more of anhydrous glucose, accurately weighed, until sufficient readings are taken. The student constructed the table shown to record the results for this experiment. [Figure table with columns A (mass of glucose /g), B (boiling point /°C), C (amount of glucose in 75.00 g of water /mol), D (Z /molkg⁻¹), E (∆T /°C)] [Figure graph grid for plotting ∆T vs Z]