A student designs two calorimetry trials to investigate the dissolution of potassium nitrate (KNO3) in water.
• Trial 1: 4.00 g of KNO3 is added to 100.0 mL of water in a Styrofoam cup calorimeter with a tight-fitting lid.
• Trial 2: The same mass of KNO3 is dissolved in 100.0 mL of water in an open glass beaker placed on the lab bench.
For each trial the water is initially at 24.0∘C, and the lowest temperature reached is recorded. The student observes a drop to 20.2∘C in Trial 1 but only to 22.5∘C in Trial 2.
(1) For Trial 1, calculate the magnitude of heat q (in joules) associated with the dissolution, assuming the solution mass equals the mass of water and a specific heat capacity of 4.18Jg−1∘C−1. Include units and sign.
(2) Based on the calculated q, classify the dissolution of KNO3 as endothermic or exothermic. Explain how the temperature data support your classification.
(3) Explain why the temperature drop in Trial 2 is smaller than in Trial 1 even though the same quantities of solute and solvent are used.
(4) Discuss how the difference in experimental setup between the two trials could lead to systematic error in determining the molar enthalpy of dissolution of KNO3. Suggest one modification to Trial 2 that would reduce this error and justify your suggestion.