Question

The osmolarity of \(0.2 \mathrm{M}-\mathrm{Na}_{2} \mathrm{SO}_{4}\) is (a) \(0.6 \mathrm{M}\) (b) \(0.4 \mathrm{M}\) (c) \(0.2 \mathrm{M}\) (d) \(0.8 \mathrm{M}\)

Short answer

The osmolarity of a 0.2 M Na2SO4 solution is 0.6 M.

Step-by-step solution

Understanding Osmolarity

Osmolarity is the measure of solute concentration defined as the number of osmoles of solute per liter of solution. For ionic compounds like Na2SO4, it dissociates in water into its constituent ions. Sodium sulfate (Na2SO4) dissociates into 2 sodium ions (Na+) and one sulfate ion (SO4^2-), therefore, producing a total of 3 particles per formula unit.

Calculating the Total Osmolarity

To find the osmolarity of the Na2SO4 solution, multiply the molarity of the solution by the number of particles it dissociates into in solution. In this case, multiply the molarity (0.2 M) by the number of particles produced upon dissociation (3): osmolarity = molarity * number of dissociated particles.

Determining the Correct Answer

Calculate the osmolarity of 0.2 M Na2SO4 as follows: 0.2 M * 3 = 0.6 M. So the osmolarity of a 0.2 M Na2SO4 solution is 0.6 M.

Key concepts

Understanding Physical Chemistry

Physical chemistry is a sub-discipline of chemistry that focuses on understanding the physical properties of molecules, the forces that act on them, and the reactions they undergo. This branch of chemistry deals with principles and methodologies that allow us to calculate and predict how chemical substances will behave under different conditions.

In the context of osmolarity calculations, physical chemistry combines concepts from thermodynamics, equilibrium, and kinetic theory to describe and analyze the dispersal of solute particles in solvent. This intersection of chemistry and physics is essential for comprehending how substances dissolve and interact in solution, which in turn is a fundamental aspect of understanding osmolarity.

Osmolarity itself is a term that reflects how solutes (like salts or sugars) can affect the properties of a solution, especially in relation to biological systems and applications such as dialysis, where maintaining proper osmotic balance is crucial.

Deciphering Solution Concentration

Solution concentration is a quantitative measure of the amount of solute that is dissolved in a given quantity of solvent. There are several ways to express solution concentration, with molarity being one of the most common units in chemistry. Molarity is defined as the number of moles of solute per liter of solution, represented by the unit M (mol/L).

Understanding the concept of molarity is vital when performing osmolarity calculations because it directly relates to the number of particles in a solution. For example, in the original exercise, a molarity of 0.2 M for Na2SO4 implies there are 0.2 moles of Na2SO4 in 1 liter of solution. However, because Na2SO4 is an ionic compound, it dissociates into individual ions, and these ions collectively contribute to the osmolarity of the solution.

Students should remember that solution concentration is not always directly proportional to osmolarity because the dissociation of solutes into their constituent ions must be taken into account, which leads us into the role of ionic dissociation in osmolarity.

Ionic Dissociation and Its Impact on Osmolarity

Ionic dissociation is the process by which an ionic compound separates into its positive (cation) and negative (anion) ions when dissolved in a solvent, like water. The extent to which a solute dissociates is crucial in calculating the actual osmolarity of a solution since each ion contributes to the total osmotic effect.

For instance, sodium sulfate (Na2SO4) dissociates into three ions - two sodium ions (Na+) and one sulfate ion (SO4^2-) - when dissolved. This means each unit of Na2SO4 generates three particles that affect osmolarity. The exercise provided emphasizes that it's not the initial concentration of Na2SO4 that matters, but rather the total number of dissociated particles it forms.

The correct calculation of osmolarity includes accounting for the dissociation of ionic compounds and is crucial for various applications, including medical treatments and the manufacturing of pharmaceuticals. Students should remember to always consider the number of ions produced upon dissociation when calculating the osmolarity to accurately represent the solution's ability to exert osmotic pressure and affect biological processes.