To divide an aqueous solution into two parts has two aspects when children recognize it. For one aspect is whether children really understand the phenomenon of “dissolve.” What is more, how children think the phenomena of “saturation” and “preservation.” Then, this paper is intended as an investigation of the state of children’s cognition before learning of the aqueous solution to use the situation to divide the aquueous solution into two parts. The findings of this investigation was the following five patterns how children to understand the density of aqueous solution. Every pattern but A is not scientiffically correct. A. Children who think that the aqueous solution’s density consists of solute and solvent. B. Children who think that the aqueous solution’s density consists of solute only and they confuse the concept of solvent with the aqueous solution. C. Children who think that the aqueous solution’s density consists of solvent only and they can think the concept of solute in the aqueous solution. D. Children who think that the aqueous solution’s density consists of its volume only and they cannot think both the concept of solute and solveny. E. Children who think that the aqueous solution’s density depends on its colour and muddieness. From our observations, we point out the ideal way of teaching on science education which have made sufficient use the children’s ideas to construct it scientifically ones.

The purpose of this research is to survey students’ naive theories of the buoyancy of objects in water, ranging from lower secondary school students to university students. In particular, we examine the relationship between the students’ naive theories on the shape of an object and those on the depth the object sinks in the water; we also investigate a naive theory related to the shape of the object, the so-called “flat theory,” i.e., that flat objects are more buoyant than cubic or spherical objects of the same volume and mass. In addition, we consider the relationship between the "flat theory" and problem-solving methods in school. Six tasks were conducted. The main findings from this research are as follows: 1) many students construct both theories related to the shape of an object and theories related to the depth the object sinks in the water; 2) many students propose the “flat theory” as a naive theory related to the shape of the object; 3) over 50% of the students who correctly solve school tasks apply the "flat theory" to other tasks.