Sugar, like salt, dissolves easily when mixed with water. The sugar molecules break up easily and do not reform again after the water molecules pull them away from each other like magnets do to iron fillings. The attraction between the water and sugar molecules depends on the charge each one emits. The sugar molecules are known to have hydroxyl groups that have a slight negative charge. On one hand, the positive charge of the oxygen found in the water molecule binds with the sugar and forms a shell that shields it from other sugar molecules. This shield prevents the sugar from clumping together.
Sometimes Sugar Does Not Dissolve Completely
There are instances that the sugar may not dissolve completely. One reason may be the solution was not stirred vigorusly enough. Another reason is that the solution is too cold before the sugar was mixed into it.
Before sugar dissolves completely, the solution has to be agitated first either through stirring or shaking. The molecules inside the container move around, hitting each other. When the water and sugar molecules collide, the sugar breaks up and binds with the water molecules. Then the water molecules spread out to make room for the sugar molecules.
When the solution is not agitated properly, the sugar will settle down the bottom, but it will not stay for long that way. The sugar molecules will still dissolve but it will take time to do so.
Heating it up speeds up the process
There is that second law of thermodynamics which states that adding heat energy to a system, such as a solution, will increases the movement of molecules in the solution. When heat energy is added to a sugar and water solution to increase the temperature, the movement of molecules is also increased. This way the sugar dissolves faster because heat encourages the water molecules to expand and make room for the sugar.
Other sugars
Aside from sucros, which is the chemical name for table sugar, there are other sugars: glucose and fructose. Just like their sister, glucose and fructose can easily dissolve in water. They also react positively when exposed to heat. These sugars are what we’d call water soluble substances.
What about salt?
Like sugar, salt will also dissolve faster when exposed to heat. This can be observed especially when salt is mixed with one’s cooking. Gases, on the other hand, do not dissolve as quickly in water when heated. This may be the reason why carbonated drinks must be kept in a cold place so the gas molecules will continue to mix in with the liquid. Otherwise, the drink will have lost its “fizz” when it’s been left in warm storage for long.
Salt Conducts Electricity, Sugar Does Not
When salt is mixed with water, it breaks up into charged particles called ions. This allows the saline solution to conduct electricity, which is the reason why they are called electrolytes. Sugar, on the other hand, does not break up into charged particles. They are called non-electrolytes.
Further Readings: