Which of the following solutions are isotonic with respect to one another? 1\. \(0.15 \mathrm{M}\) urea 2\. \(0.05 \mathrm{M} \mathrm{CaCl}_{2}\) 3\. \(0.1 \mathrm{M} \mathrm{MgSO}_{4}\) 4\. \(0.15 \mathrm{M}\) glucose Select the correct answer using the codes given below: (a) 1 and 4 (b) 1,2 and 4 (c) 2 and 3 (d) 2,3 and 4

Tonicity is a term that primarily concerns how the concentration of solutes in a solution can affect the movement of water across a cell membrane. When solutions are separated by a semipermeable membrane, which only allows certain types of substances to pass through, water can move back and forth in order to balance solute concentrations on both sides.

This movement of water is driven by osmosis, which aims to reach an equilibrium. Imagine two glasses of water, one with salt dissolved in it and one without. If you connected these glasses with a tube that only lets water through (just like a cell membrane), water would flow from the unsalted water to the salted water, attempting to dilute it.

An isotonic solution is where the concentration of solutes is equal on both sides of the membrane, so there's no net movement of water. Cells in an isotonic solution are stable, with no shrinkage or swelling. This stability is crucial for cells to maintain their shape and function properly, making tonicity an important concept in biology and medicine.

Osmolarity represents the concentration of solute particles in a solution and is a key factor in determining a solution's tonicity. It is often measured in osmoles per liter (ol₋₁). Since osmolarity accounts for all particles that contribute to a solution's concentration, it reflects the solution's ability to draw water through osmosis.

With non-electrolytes (substances that don't dissociate into ions in solution), such as glucose or urea, the osmolarity is identical to their molarity because they do not break down into smaller particles. Conversely, for electrolytes, substances that do ionize in solution like CaCl2 or MgSO4, you must take into account that they separate into multiple particles. For instance, CaCl2 separates into three particles (one Ca2+ and two Cl−), thereby tripling its contribution to the osmolarity of the solution compared to its molarity.

Understanding osmolarity is valuable for applications including medical treatments like intravenous infusions, where the osmolarity of administered solutions must be compatible with bodily fluids to avoid cell damage.

Solution concentration is a quantitative measure of the amount of solute that is dissolved in a given quantity of solvent or solution. It is a fundamental concept in chemistry as it influences various properties of the solution, such as boiling point, freezing point, vapor pressure, and, as discussed above, osmolarity and tonicity.

Concentration can be expressed in different forms, such as molarity (M), which is moles of solute per liter of solution. When you come across solutions with different salts or compounds, it’s not straight-forward to compare them just by their molarity. Instead, you should calculate their osmolarity to fully understand their potential impact on cells.

Calculating the concentration of solutions accurately is essential in chemical reactions, where precise reactant ratios are crucial to obtain the desired products. It's also vital in medical settings to ensure that the fluids administered to patients are at the correct concentration to avoid harmful effects.