A researcher investigates the uniformity of a sugar solution prepared by dissolving…
CHEMISTRY · Multi-part · CBSE · Chemistry · Is Matter Around Us Pure? · Is Matter Around Us Pure?
Problem
A researcher investigates the uniformity of a sugar solution prepared by dissolving 180 g of sucrose in enough water to make 1.00 L of solution. Immediately after preparation, the researcher measures the electrical conductivity at three radial positions inside the beaker—center (0 cm), midway (3 cm), and near the wall (6 cm). The measured conductivities are listed below.
Radial Position (cm)
Conductivity (mS·cm−1)
0
0.372
3
0.371
6
0.373
(a) On the basis of the data, classify the sugar solution as homogeneous or heterogeneous. Support your answer with explicit reference to how conductivity relates to the distribution of dissolved species.
(b) The researcher then places the beaker in a freezer at –5 °C for 2 h, during which ice crystals form primarily at the inner wall. After 2 h, conductivity is re-measured at the same three radial positions and found to be 0.410 mS·cm−1 at 0 cm, 0.389 mS·cm−1 at 3 cm, and 0.115 mS·cm−1 at 6 cm. Re-classify the contents of the beaker and justify the change, if any, in classification.
(c) Explain why freezing can convert an initially uniform sugar solution into a system whose macroscopic properties vary with position. Your explanation should integrate principles of phase change and solute distribution.