Animated Solution for Chemistry - Solutions: The size of a raw mango shrinks to a much smaller size when kept in a concentrated salt solution. Which one of the following processes can explain this?

Mango Meets Salt

Imagine you drop a plump, raw mango into a beaker filled with a highly concentrated salt solution.

At first glance, it seems like a simple kitchen experiment. But at the microscopic level, a fascinating battle of pressures is about to begin.

The skin of the mango is not just a boundary; it acts as a semi-permeable membrane. This means it acts like an exclusive VIP bouncer, allowing only certain tiny molecules—like water—to pass through, while blocking larger solute particles like salt.

Inside the mango, the cell cytoplasm has its own natural concentration of solutes. Let's call this internal concentration $C_1$.

Outside the mango, we have our artificially prepared salt solution. Because it is highly concentrated, its concentration, let's call it $C_2$, is much higher than the inside.

Mathematically, we can state our primary constraint: $C_1<C_2$.

This concentration gradient is the driving force for everything that follows.

To understand the physics of the flow, we need to bring in the master equation for osmotic pressure:

Here, $R$ is the universal gas constant and $T$ is the temperature. Since the entire system is at the same room temperature, the osmotic pressure $\pi$ is directly proportional to the concentration $C$.

Let's apply this to our two regions. Inside the mango, the osmotic pressure is ${\pi }_1=C_{1}RT$.

Outside in the salt bath, the osmotic pressure is ${\pi }_2=C_{2}RT$.

Exo-Osmosis

Because the outside concentration is greater ($C_1<C_2$), it mathematically guarantees that the outside osmotic pressure is greater:

Nature absolutely despises imbalance. To equalize this massive pressure difference, the system tries to dilute the highly concentrated outside solution.

Since the salt cannot enter the mango due to the semi-permeable membrane, the solvent—water—must make the journey. Water molecules rush out from the region of lower concentration (inside the mango) to the region of higher concentration (the salt bath).

This outward flow of water is scientifically known as exo-osmosis.

As the water leaves the cells, the cytoplasm loses its volume and pressure. The biological result? The cells undergo plasmolysis, and the entire raw mango visibly shrinks!

This isn't just textbook chemistry; it's the ancient secret to making pickles!

By soaking raw mangoes in salt, we intentionally trigger exo-osmosis to draw out excess water.

Without water, bacteria and fungi cannot survive, allowing the pickled mangoes to be preserved safely for months. Chemistry is truly delicious!