When a gummy bear is dropped into water, it undergoes a dramatic transformation, growing many times its original size over several hours. It does not simply dissolve like a sugar cube. This common experiment illustrates fundamental physical and chemical principles, showing how molecular structure and concentration gradients govern water movement. The resulting changes in size and texture are directly linked to the bear’s unique composition and its interaction with the surrounding liquid.
The Science Behind the Gummy Bear Structure
The gummy bear’s physical behavior is determined by its primary ingredients: sugar and the polymer gelatin. Gelatin, derived from animal collagen, forms a vast network of long protein chains. This network acts as the structural framework for the candy, trapping sugar and corn syrup inside.
This gelatin matrix functions like a semi-permeable barrier, allowing some molecules to pass through while blocking others. Water molecules are small enough to move easily through the microscopic gaps within the protein mesh. However, the much larger sugar molecules are trapped within the structure. This internal composition sets the stage for the dramatic reaction that occurs when the candy is submerged in pure water.
How Water Swells the Gummy Bear
The significant increase in the gummy bear’s mass and volume is explained by osmosis. Osmosis is the passive movement of water across a semi-permeable membrane from an area of high water concentration to an area of low water concentration. Pure water represents the area of high water concentration because it contains virtually no dissolved solids.
The gummy bear is a highly concentrated solution of sugar and other solutes, meaning it has a low concentration of water. Since the gelatin structure allows water to enter but prevents the trapped sugar from leaving, a strong concentration gradient is established. Water molecules rush into the gummy bear through the gelatin network to dilute the high sugar concentration inside and achieve equilibrium.
This influx of water causes the internal structure to swell considerably, often increasing the candy’s weight and volume by several hundred percent. A single gummy bear can absorb enough water to reach a final mass of over 10 grams. As the gelatin network absorbs this volume of liquid, the candy loses its original firmness, becoming soft and squishy.
Experimenting with Different Liquids
The extent of the gummy bear’s swelling depends on the solute concentration of the liquid, which directly affects the osmotic pressure. If the bear is placed in a solution with a high concentration of solutes, such as heavily salted water, the osmotic gradient is significantly reduced. The lower water concentration outside the bear slows the rate of water absorption compared to pure water.
If the external solution is more concentrated than the inside of the gummy bear, water will move out of the candy. This process causes the gummy bear to shrink or shrivel as it loses internal moisture. The concentration of the surrounding liquid determines the direction and magnitude of the water movement, illustrating the balance of osmosis.
Other liquids can introduce chemical effects alongside the osmotic process. Placing a gummy bear in an acidic liquid, like vinegar, still results in some water absorption and swelling. However, the low pH of the vinegar begins to chemically break down the protein chains of the gelatin. This simultaneous chemical reaction causes the gummy bear to become not only soft but also structurally unstable, often resulting in dissolution over time.