CTS Guide: Mixtures and Solutions, pp 158-159- Section IV Research Summaries

Dissolving

• Studies show young children have difficulty distinguishing between melting and dissolving. “Although two materials are required for the dissolving process, children tend to focus only on the solid and they regard the process as melting” (Driver et al. 1994, p. 80). When things dissolve they often describe them as “melting away.” When things melt, children have described them as being similar to “ice going runny.”

• From an early age through to adulthood, conceptions about dissolving include the following: the solute “disappears,” “melts away,” “dissolves away,” or “turns into water.” Older students imagine that as sugar dissolves, it “goes into tiny little bits,” “sugar molecules fill spaces between water molecules,” or sugar “mixes with water molecules” (Driver et al. 1994).

• Cosgrove and Osborne (1980) sampled 8- to 17-year old children and found that they regarded melting and dissolving as similar processes since they were both gradual. They also found that melting was unconnected to the concept of a particular melting point.

• In a study that looked at how students perceive dissolving, some middle school students thought sugar melts away when dissolved in water (Lee at al. 1993).

Solutions

• Students’ ideas about solutions include thinking that sugar solutions are not a single phase but rather that invisible particles of sugar are suspended in the solution. They may suggest that the particles can be filtered out or will settle out from the solution. Others see the solute and solvent as a single substance rather than as a homogeneous mixture (Driver et al. 1994).