Final answer:
To calculate the mass of pyrazole needed to lower the freezing point of camphor by 15°C, use the freezing point depression formula, solve for the molality, then convert to moles, and use the molar mass to find the required mass of pyrazole.
Step-by-step explanation:
To determine the number of grams of pyrazole (C₃H₄N₂) needed to lower the freezing point of camphor by 15 degrees Celsius, we apply the freezing point depression formula ΔTf = i • Kf • m, where ΔTf is the change in freezing point, i is the van't Hoff factor (which is 1 for non-electrolytes like pyrazole), Kf is the freezing point depression constant for the solvent, and m is the molality of the solution.
Since pyrazole is a non-electrolyte, we can assume i = 1. We then rearrange the freezing point depression formula to find the molality (m) needed to produce the desired ΔTf. Next, we convert the molality to moles of pyrazole using the mass of the solvent (camphor), and finally, use the molar mass of pyrazole to find the mass required.
The calculations for this question would closely follow the example of finding the molar mass of the solute given the lower freezing point of the solution using the provided constant for camphor (40 degrees C per m) and the steps outlined in similar calculations. For instance, in example 68, the calculation procedures to determine the molar formula of a solute involve several steps which are analogous to solving this camphor-pyrazole problem.