Chemistry · Solutions · NEET
Compare the outside solution to what is INSIDE the cell. Isotonic = same osmotic pressure as the cell fluid, so no net water movement and the cell stays normal. Hypertonic = MORE concentrated than the cell, so water leaves the cell and it shrinks (crenation). Hypotonic = LESS concentrated than the cell, so water enters the cell and it swells (and can burst). NCERT uses 0.9% (mass/volume) NaCl as the reference: equal to it = isotonic, more than it = hypertonic, less than it = hypotonic.
The outside solution has more solute, so it has higher osmotic pressure. Water always moves from the LOW solute side to the HIGH solute side through the membrane. So water flows OUT of the cell into the solution, and the cell shrinks (shrivels). NCERT gives the pickle example: a raw mango in strong salt water loses water and shrivels for the same reason.
A hypotonic solution is more dilute than the cell fluid (less than 0.9% NaCl). Water moves toward the more concentrated side, which is INSIDE the cell. So water flows into the cell and it swells. This is why wilted flowers or a limp carrot revive in fresh water, and why blood cells swell in low-salt water.
Yes. NCERT says the osmotic pressure of the fluid inside a blood cell equals that of 0.9% (mass/volume) NaCl, called normal saline. Because it is isotonic, injecting it causes NO net water flow into or out of the blood cells, so the cells are not damaged. That is why it is safe to give intravenously.
In normal osmosis, pure solvent (water) flows INTO the concentrated solution on its own until osmotic pressure builds up. In reverse osmosis you apply a pressure LARGER than the osmotic pressure on the solution side, which forces the flow backwards: pure water is squeezed OUT of the solution through a semipermeable membrane. NCERT's key use is desalination of sea water to get drinkable water, using membranes like cellulose acetate that pass water but block ions.
Water moves from the solution of LOWER solute concentration (more dilute, lower osmotic pressure) to the solution of HIGHER solute concentration (more concentrated, higher osmotic pressure). In short: solvent moves toward the more concentrated solution. Do not confuse this with diffusion of the solute itself.
The following solutions were prepared by dissolving 10 g glucose (C6H12O6) in 250 mL of water (P1), 10 g of urea (CH4N2O) in 250 mL of water (P2) and 10 g of sucrose (C12H22O11) in 250 mL of water (P3). The right option for the decreasing order of osmotic pressure of these solutions is:
The plot of osmotic pressure (π) vs concentration (mol L⁻¹) for a solution gives a straight line with slope 25.73 L bar mol⁻¹. The temperature at which the osmotic pressure measurement is done is: (Use R = 0.083 L bar mol⁻¹ K⁻¹)
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Look at the prefix. HYPER means over/more, so a hypertonic solution has more solute than the cell and pulls water out (cell shrinks). HYPO means under/less, so a hypotonic solution has less solute and pushes water in (cell swells). Iso means equal, so no net flow.
No. Isotonic solutions have equal osmotic pressure, so when separated by a semipermeable membrane there is no NET osmosis. This is why isotonic saline (0.9% NaCl) is safe to inject into blood.
It is a direct one-line NCERT fact: reverse osmosis uses pressure greater than the osmotic pressure to push pure water out of a solution, and it is used for desalination of sea water. Questions often just ask its definition or its main application.
Osmotic pressure is a colligative property, so it depends on the NUMBER of solute particles, not their nature. For electrolytes you must include the van't Hoff factor i, which raises the effective particle count and the osmotic pressure — that is the next concept to learn.
Yes. Tonicity is always relative. A given solution can be hypertonic (more concentrated) compared with a dilute solution and hypotonic (more dilute) compared with a stronger one at the same temperature. Always compare the two specific solutions.
