Question

28. Investigating changes in colligative properties involves the measurement of a solution's concentration in molality instead of molarity because (2 points)

the mass of the solvent does not change, but its volume does change, as temperature changes.
the volume of a solution can be measured more accurately than the mass of a solution.
the volume of a solution does not change, but its mass does change, as temperature changes.
the mass of a solvent can be measured more accurately than the volume of a solvent.

Answer 1

In chemical reactions, mass is always constant, so the third choice is wrong. Hopefully you know that the volume of any substances will expand if it's heated up (few exceptions like frozen water and some rare other compounds). Regardless of expanding or contracting, the volume still changes in some way.

So think about it for a second. When you're measuring colligative properties, especially boiling and freezing point elevation/depression, it's often done at non-room temperature, so the volume is BOUND to CHANGE. It's really hard to measure these subtle changes accurately, and even if you can measure it, it's a pain to keep this in consideration. Since mass doesn't change (you should have learned about conservation of mass in your chemistry class), you don't have to keep track about its changes during a reaction/observation. You eliminate one unknown out of the consideration so it's easier

Recap: I'm talking about the CHANGE here. Volume does change, mass doesn't. Both of these are easy can be quite accurately measured at constant temperature.

Think about which is the right answer and comment here. I'll tell you if it's right or not